Docstoc

INFLIBNET Centre Ahmedabad Gujarat INDIA

Document Sample
INFLIBNET Centre Ahmedabad Gujarat INDIA Powered By Docstoc
					                                                                                     INTRODUCTION



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                                  Organisms are endowed with two environments, an external

                   environment (milieu exterieltr) and an internal environment (milieu inteneur).

                   The mechanisms by which the body responds to various disturbances are

                   centred around the concept of internal environment, the stability of which

                   is maintained to preserve life. Animals have developed complex mechanisms

                   to maintain the constancy of their internal environment. Cannon ( 1 935)

                   coined the term homeostasis to characterize the co-ordinated physiological

                   processes which maintain the internal steady state by the integrated

                   activity of a wide range of organ functions. The internal steady state

                   may vary within narrow limits based on regulatory abilities or adaptational

                   range. The regulated physiological parameters can be extended to the

                   cellular and enzyme level, being ultimately controlled by the genetic

                   system. The less specialized animals operate over much wider ranges of

                   environmental conditions than the more complex forms. Among them

                   tissues function over wide ranges of adjustments of the internal environment;

                   whereas in higher vertebrates a relatively stable internal environment is

                   maintained by regulation (Prosser, 1955).


                   A.     Definition of Stress and General Considerations

                                  Disturbances i n the external environment initiate stimuli i n

                   sensory receptors leading to internal regulatory responses contribut~ng

                   to homeostasis. These responses may be brief, or long lasting, but can


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                  often be tolerated indefinitely without adverse effects by an individual.

                  Of greater impact are environmental impositions which are sufficiently

                  intense or prolonged to make even the maximum response inadequate to

                  maintain homeostatic balance and s o the individual experiences adverse

                  effects. In such situations the animal is said to be under stress, a common

                  term used to describe situations where an animal i s under difficulties

                  and cannot cope with the imposed demands.

                                 Coping andfitness are two terms associated with stress. There

                  is wide spread view that stress has adverse effects which often include

                  some reference to a prolonged inability to cope with conditions (Archer,

                  1979). When an animal is subjected to a noxious stimulus, its biological

                  response i s either adequate to maintain stability enabling the animal to

                  cope, or it is inadequate, and the animal does not cope. In this sense

                  coping i s an indicator of the success the animal achieves in controlling

                  its internal environment; and hence, to cope is to have control of mental

                  and bodily stability (Fraser and Broom, 1990).

                                 T h e i d e a that stress is something that reduces individual

                  fitness has been put forward by Broom (1983, 1985), and Fraser and

                  Broom (1990). The fitness depends on the genotype and on several basic

                  life cycle variables like age and breeding (Charlesworth, 1980). The

                  effect of an environment on an individual is detrimental if the fitness of



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   that individual is reduced, and in some cases inadequate fitness is clearly

                   visible and can be measured (Hofer, 1970; Liang et a l . , 1979; Baum,

                   et a ] . , 1982; Odio et al., 1986)

                                  It is best to define stress as an 'effect' so that it i s quite clear

                   that the organism is changed by some outside variable. The impact of

                   s t r e s s i s to c a u s e some, or all o f t h e control systems within the

                   individual to work too hard for effective functioning (Broom and Johnson,

                   1993). In a general way stress can be considered as an environmental

                   effect on an individual, which overtaxes its control systems and reduces

                   its fitness. There will normally be a reaction on the part of the individual

                   to such an effect. This i s stress response a n d the immediate and

                   short-term consequences of the stress constitute strain. It matters, whether

                   it lasts for a short period or for much o f the animal's life, if the animal

                   is unable to cope with it. However, distinction has to be made between

                   minor disturbances to an animal's equilibrium which may result in the

                   use of energy to correct them, but have no consequences for fitness, and

                   those disturbances which do, or are likely to, reduce fitness.

                                  Studies in stress physiology commenced with the pioneering

                   works of Hans Selye during the middle part of this century. To Selye the

                   force acting on the animal causing stress is a stressor; and stress is the

                   adaptive responses comprising progressive series of reactions and viewed


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   it as a syndrome, termed General Adaptation Syndrome (Selye, 1946,

                   1950, 1973, 1976; Gorbman and Bern, 1962; Archer 1979). Selye argues

                   that the increased activity of the adrenal cortex producing more

                   adrenocortical hormones is a stress response, and it is an attempt to adapt

                  to sustained injurious or noxious environmental changes. Exhaustion of

                  adrenocortical function leads to the loss of organism's ability to

                  sustain its physiological adaptation, leading to lethal effects and death.

                                 The general adaptation syndrome is the sum of all non-

                  specific systemic reactions of the body which ensue upon continued

                  exposure to stress and is characterized by three stages or phases. The

                  first stage occurs immediately on exposure to a stressor and is called

                  alarm reaction which involve some of the immediate responses of the

                  body associated with sympatho-adrenomedullary discharge. Following this is

                  the second stage, a stage of resistance, when the organism is continued

                  to be exposed to the stressor during which hypothalamic-pituitary-

                  adrenal cortical axis is activated and adrenal hypertrophy, lymphoid shrinkage,

                  changes in immune function, gastrointestinal ulceration and other symptoms

                  develop. The third stage is the stage of exhaustion when the sustained

                  injurious stimulus finally begins to have its full impact upon the organism

                  with an apparent failure of adaptive mechanisms resulting i n death

                  (Selye, 1946, 1950, 1973, 1976; Gorbman and Bern, 1962; Archer, 1979;

                  Kelly, 1980; Kopin et a l . , 1989).

Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                                  There has been much research on problems related to animals

                    under stress since 1950's. especially on the behaviour and physiology of

                   rodents and other mammals under social stress conditions such as crowding

                   (Christian, 1963; Archer, 1970; McGrath, 1970; Sakellaris and Vernikos,

                    1975; Shively and Kaplan, 1984; Bohus et al., 1987). The reasons for

                   socially induced stress in animals have become more complex and this

                   area of research is of interest to endocrinologsts, ethologsts and experimental

                   psychologsts. Investigations on animals under stress also have applied

                   implications in the field of animal welfare. Modern methods of large

                   scale intensive farming, which is usually unnecessarily restrictive and

                   harsh, lead to situations adversely affecting animal welfare and hence

                   agriculturists and veterinarians have discussed them in terms of stress

                   concept (Henry, 1976; Stephens, 1980; Gross and Siegel, 1981; Hurnik

                   and Lehman, 1988; Parrott, 1990; Broom and Johnson, 1993)

                                  Selye's studies on stress laid emphasis on the non-specific

                   common physiological responses to stress such as the secretion of adrenal

                   glucocorticoids, suppression of the immune system and the formation of

                   gastrointestinal ulcers to a variety of different environmental conditions

                   (Selye, 1950. 1973; Archer, 1979; Stott, 1981; Dantzer and Mormede,

                   1983). But physiological response to stress is much more varied than

                   what Selye contended, since the neuroendocrinological and other



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   biological responses to adversity are so diverse and stimulus dependent,

                   that, even when similar physiological responses follow different adverse

                   stimuli, the pattern is by no means uniform and hence,relatively more

                   specific (Mason, 1968, 1971, 1975; Moberg, 1985, 1987; Trumbull and

                   Appley, 1986). Not only the neuroendocrinological but also the behavioural

                   and immunological responses to noxious stimuli extend across considerable

                   ranges (Kelly, 1980; Stein et al.,1985; Glaser et a/.,
                                                                        1985; Esterling et

                   al.,1987). Mason (1 968, 1971, 1975) also emphasized the greater importance

                   of the emotional reaction or psychological component in the stress response.

                                  Bohus et al. (1987) viewed stress as a general biological and

                   usually functional response to environmental and bodily demands, and

                   depends on interaction between environment with stressors of varying

                   intensity and duration, and the specific or non-specific body responses

                   co-ordinated by the nervous and endocrine systems. The animal tries to

                   adapt to the situation by physiological adjustments within tolerable

                   limits, maintaining homeostasis. Short term and long term consequences

                   have been observed depending on the intensity and durability of the stressor

                   (Broom and Johnson, 1993).

                                  Responses to adverse environmental condrtions involve complex

                   interactive network of relationships among various parts of the brain and

                   body. Peptides such as corticohopin releasing hormone,            P-   endorphin and

                   others having diverse effects within the brain and body are released which


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    vary with the levels of other peptides present at the time (Anil et al.,

                    1990; Al- Gahtani and Rodway, 1991). Further, it has been found that

                    the adrenal cortex and immune system have feed back effects on the release

                    of peptides that are active in the brain. Effective opioid peptides include

                    p- endorphin, enkephalins and dynorphin, the receptor sites for which
                    exist in the brain and other parts of the body as well as on lymphocytes

                   (Bartrop et a/.,                                    1985; Kalin et a/.,
                                   1977; Akil et al.,1984; Baker et a/.,

                    1985; Kant et al.,1986). Apparently no single stress response, but rather

                   a wide range of physiological and other changes, which although overlapping

                   in some components, are usually quite specific to circumstances.

                                  Glucocorticoids are released in response to situations that are

                   also not normally regarded a s stressful, which include courtship,

                   copulation and hunting (Broom, 1988). Species differences exist, and

                   certain stimuli that elicit an undoubted adrenal response in one species

                   cause little or no effect on others (Freeman, 1987). As a result, in many

                   circumstances because of the poor correlation with adverse effects, adrenal

                   indices alone are considered questionable indicators of stress ( Moberg,

                   1987).

                                  Physiological status of the animals under stress has been better

                   discussed by various investigators (Dantzer et a / . ,1980; Bohus et a/..
                                                                                           1987;

                   Kopin        el a/.,1989 ; Nielsen, 1994) and have brought to light the



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   co-ordinated activities of the nervous, endocrine and metabolic

                   machinery to tide over the adverse situations. Measurements of the

                   activity in the hypothalamo-adrenal medullary system and in the

                   hypothalamic-pituitary-adrenal cortex system are amongst the most

                   useful in the assessment of how difficult it is for animals to cope with

                   short term problems (Maiser et al., 1986; Gaillard and Al-Damluji, 1987).

                   Both systems cause changes in the body which alter the range of

                   substrates available for emergency action: more glucose after adrenomedullary

                   hormones, more amino acids and fatty acids after cortisol (Gorbman and

                   Bern, 1962; Granner, 1993a). These lead to the ready release of energy

                   for emergency action. However, the two systems differ in their time course

                   in that adrenal medulla hormones are shorter lived than adrenal cortex

                   hormones, and adrenal cortex activity has more long term effects (Granner,

                   1993a).

                                  The principal products of the adrenal medullary response to

                   emergency situations are the catecholamines, epinephrine (adrenaline)

                   and norepinephrine (noradrenaline). In human emotional disturbances of

                   the kind, which elicit a more passive response, cause a greater increase

                   in adrenaline production, and those disturbances which are associated

                   with physical activity ( particularly aggression) cause a greater increase

                   in the noradrenaline production (Mason, 1968; Frankenhaeuser, 1975;

                   Goldstein, 1987). The release of these catecholamines from the adrenal


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                      medulla occurs within one or two seconds of the perception of the initiating

                      stimulus, but their metabolism is very rapid; the half life of which in rat

                      blood being 70 seconds (Mc Carty, 1983). The catecholamine levels in

                      suddenly disturbed rats showed about a 40-fold adrenaline and 6-fold

                      noradrenaline increase (Kvetnansky et al., 1978) and almost similar results

                      were obtained by Turch and Vogel(1980), Livesey et al., (l985),'Castagne

                      er al.. (1987) and Konarska e t al., (1989).

                                     The first stage of activity in the hypothalamic-pituitary-

                      adrenal cortex system i s interleukin 1                        P stimulated secretion of
                      corticotropin releasing hormone (CRH). The release of adreno-

                      corticotropic hormone (ACTH) from the adenohypophysis is

                      initiated principally by CRH, although it can also occur in response to

                      catecholamines (Axelrod, 198J), or to neurohypophyseal hormones,

                      arginine-vasopressin and oxytocin (Gibbs, 1986; Gaillard and AI-Damluji,

                      1987). ACTH is carried by the blood to the adrenal cortex where the

                      glucocorticoids (cortisol and corticosterone) are released. The production

                      of ACTH and CRH is inhibited by glucocorticoids by feedback

                      mechanisms. There is greater delay for the release of glucocorticoids (at

                      least two minutes) into the blood stream than for adrenaline and

                      noradrenaline released from the adrenal medulla. The sequence of

                      production of CRH, ACTH and adrenal hormones have been studied in



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    animals subjected to different stress conditions (Fell and Shutt, 1986,

                    Parrott e f a / . , 1989; Mendl et a/., 1991).


                    B.    Stressors and Stress Impact

                                   Investigations on stress have been undertaken in relation to

                    physical, chemical and social stressors. The familiar physical stressors

                    are light, heat, noise and pressure. Light and heat (infra-red)*&&,

                    electromagnetic radiations. The electromagnetic rays sensed by the eye

                    (400nm-700nm) is referred to as visible light. All radiations of the

                    electromagnetic spectrum can generate heat in a medium, the extent of

                    heat energy production depends on the degree of interaction between the

                    radiation and the medium. Most materials in nature are good absorbers

                    of infra-red radiations and hence they get heated easily. Infra-red

                    radiations are better absorbed by the body of living organisms.


                   Light

                                  The light particle, photon, on striking an atom or a molecule

                    sends an electron into a higher energy level and making it excited. The

                    electron then drops back to the ground state after little more than lo-'

                    seconds. During this brief interval the electronic energy provided is channelled

                   for chemical reactions which                      are collectively called photochemical

                   reactions. Photochemical process of life depends on pigment molecules

                   like chlorophyll, visual pigments etc., which absorb light initiating the


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   chemical reactions (Lehninger, 1971; Giese 1979; Parson, 1989; Lehninger

                   el   al., 1993).

                                  Light which actually reaches the body surface of the organism

                   is greatly attenuated by absorption in theouter layers. Acellular organisms

                   like protozoa are especially susceptible to light because they are so thin

                   that light penetrates vital areas. In vertebrates like mammals, the penetration

                   of light is only superficial and the degree of penetration depends on the

                   extend of reflection and pigmentation (Ruch and Patton,1965).

                                  Light acts as a limiting factor for the diverse activities of organisms.

                   It regulates a number of biological processes including structural and

                   physiological characteristics of animals. Light has profound effect on

                   the metabolism, as the absorbed radiant energy may increase the rate of

                   enzyme activity, and in many cases by photodynamic action affects proteins

                   and other macromolecules adversely (Giese, 1979; Hoar and Hickman,

                   1983). Light controls the locomotory activity in lower animals and also

                   affects the development, besides its role in vision, pigmentation and

                   photoperiodism (Roy, 1996). The role of light on endocrine secretions,

                   gonads and biorhythms are well established, especially of the pineal in

                   relation to the photoperiod and reproduction (Reiter, 1978; Reiter et a ] . ,

                   1988; Blank et al., 1988). Ambient photoperiodic changes influence

                   reproduction ma., the pineal gland which acts as the transducer organ



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   whose function has been elucidated in a number of mammals (Reiter,

                   1987; Hastings et a l . , 1989; Bartness and Goldman, 1989; Ebling and

                   Foster 1989; Herbert, 1989). The studies on the pineal of a nocturnal

                   mammal like bat have elucidated its functional importance in relation to

                   light (Quay, 1976; Pevet et.al., 1977; Pevet and Racey, 1981).

                                  Enzymes and proteins have been found to be influenced by

                   photic stress. Lalitha et al. (1988) investigated the effect of flickering

                   light on albino rats and found statistically significant increase in serum

                  corticosterone, serum cholesterol, serum glutamic oxaloacetic transaminase

                  (SGOT) and serum glutamic pyruvic transaminase (SGPT), while a

                  marked reduction was seen in the serum triglyceride level. Key et al.

                  (1 992) observed the relation of liver failure under photic stress. There is

                  also evidence for the glucose regulated protein induction and cellular resistance

                  to oxidative stress mediated by porphynn photosensitization (Gomer et a l . ,

                   1991). Light acting as a stressor is found to release a group of proteins

                  called, light inducible proteins especially in plants (Adamska et al., 1992;

                  Potter and Kloppstech, 1993) and are studied in relation to physiological

                  adaptations.




                                 Like light, heat is also a form of radiant energy and temperature

                  is the measure of heat level. Although the environmental temperature is

                  highly varied, normal life activities exist within the range from about 0
                                                                                          '

Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                  to 40°C,eventhough there are a few forms which live in exceptionally lower

                  and higher temperatures (Prosser, 1973). With a rise in temperature the kinetic

                  activity or molecular collision increases, accelerating the rate of reactions

                  and          i s quantified by Q,, approximation.                  The Q,, is a
                  factor by which a reaction velocity is increased by a rise of 10°C.

                                 Heat is a by-product of many cellular biochemical reactions and

                  hence cells can broadly be considered as open thermodynarmc systems endowed

                  with regulatory and compensatory mechanisms. Temperature brings in

                  structural alterations in enzymes, their substrates and reaction kinetics during

                  the compensatory response (Hochachka and Somero, 1984;Cossins and Bowler,

                   1987). In the multicellular animals, temperature effects may be more critical

                  in one tissue or organ system than in another, eventhough all physiological

                  processes are based on enzyme catalyzed reactions (Hoar, 1984). In higher

                  vertebrates, the neuroendocrine system attains the ultimate control by regulating

                  the temperature of the entire organism, in addition to behavioural responses

                  which may assist in the adaptation to changing thermal environments.

                                 Endothems maintain a constant warm internal body temperature
                  achieved by physiological processes supported by various anatomical

                  adaptations. Most endotherms have a range of ambient temperatures within

                  which minimum oxygen consumption is required, expending little or no




Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   energy to regulate their internal body temperature, and the temperature

                   range is referred to as the thermal neutral zone, bounded by a lower thermal

                   critical temperature and an upper thermal critical temperature (Bartholomew,

                    1982). The maintenance of such a constant internal temperature is called

                   thermal homeostasis (Hensel et al., 1973; Hardy, 1978; Hill and

                   Smith, 1986).

                                  Conduction, radiation and evaporation act on an organism and

                   eventually an equilibrium point is reached between the external temperature

                   and the body temperature.                    If, however, the point of equilibrium is

                   beyond the lower thermal lethal, the organism responds physiologically

                   by generating sufficient heat to stay warm, or responds behaviourally by

                   moving to a location where the equilibrium does not exceed the lethal

                   limit. If the point of equilibrium is beyond the upper lethal limit the organism

                   must respond by either increasing its rate of heat loss or moving to a cooler

                   location to maintain its temperature within survival limits (Hensel et al.,

                   1973).

                                  In placental mammals the body temperature lies roughly

                   between 36" and 38OC ( Hoar, 1984) and that of fruit bat (Preropus sp.)

                   35"and 39°C (Prosser, i 973). The stabilization of body temperature in

                   homeotherms removes one of the variables of the internal environment

                   which permits a steady level of activity, both metabolic and locomotory

                   (Hoar, 1984). Increased external temperature stimulates the heat receptors

Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    of the skin and heat dissipation. Consequently, dilation of cutaneous blood

                    vessels occurs, resulting in an increased peripheral blood flow for heat

                    loss by the evaporation of water. If a balance is not maintained, active

                    sweating occurs in animals with sweat glands, accompanied by increased

                   respiratory ,heat loss. The loss of water by respiratory tract (pulmonary

                   ventilation), by sweat glands and evaporation from skin varies in different

                   species. Other methods of cooling like panting and liclung are also prevalent

                   among some mammals (Schmidt-Nielsen, 1979; Bartholomew, 1982).

                                  Mechanisms of heat regulation are activated by the

                   thermoreceptors in the skin, in deep organs and in various parts of the

                   central nervous system. The physiologcal thermostat in mammals is the

                   anterior hypothalamus which is responsible for protection against heat

                   (Heller et al. , 1978; Santinoff, 1978; Hoar and Hickman, 1983). When

                   cooling mechanisms fail the body temperature rises, the oxygen consumption

                   increases because of the direct cellular effect of heat and increased

                   metabolism. Such an increase in metabolism may be a part of the regulatory

                   mechanism, since it is less in thyroidectomised and hypophysectomised

                   rats (Prosser, 1973). A state of heat shock (hyperpyrexia) results when

                   the thermoregulatory centre fails and body temperature rises critically

                   leading to dehydration and change in salt balance due to the excessive

                   loss of salt. Adaptive ability of many tropical mammals to heat are genetic

                   (Prosser, 1973; Hensel et a / . , 1973).


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                                   Studies on heat shock proteins (HSP) have helped in

                    understanding the molecular mechanisms of adaptation to stress at the

                    cellular level. According to Blake et al. (1991), induction of heat shock

                    proteins by cellular stress, and the activation of the hypothalamic-

                    ~ituitary-adrenalaxis by physiological stress, are biological responses

                    that aid in the maintenance of cellular and organismal homeostasis respectively.

                    The heat shock protein (HSP 72) has been identified in rat brain after

                    hyperthermia (Li et al., 1992; Kirby et al., 1994). Kampinga (1993)

                    investigated the thermotolerance ability of mammalian cells and observed

                    that the cells that have been pre-exposed to thermal stress can acquire a

                    transient resistance against the killing effect of a subsequent thermal stress.

                    It has also been shown that the thermal stressed rats acquire thermotolerance

                    by evoking specific heat shock proteins (De Maio et al., 1993; Nakajima

                    et al., 1992). Dokas et al. (1994) reported corticosteroid induced stress

                    proteins in brain, and Blake et al. (i991) noted the expression of

                    specific heat shock protein in adrenal cortex corresponding to heat shock.

                    Exposure to hyperthermia has also been found to affect blood chemistry

                    in rabbits (Marder et al., 1990), blood cells in man (Keatinge et al., 1986;

                    Utoh and Harasaki, 1992) and chicken (Trout and Mashaly, 1994). enzyme

                    pattern, glucose kinetics and transport (Widnell e t a / . . 1990; Hargreaves

                    et a / . , 1996).



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    Noise

                                   Excessive noise is considered a potentially serious stressor and

                    a pollutant causing stress reactions. Rosecrans et a / . ( 1 966) had reported

                    higher blood pressure, elevated epinephrine and corticosterone levels in

                    the blood of albino rats subjected to sound stress. Apart from increased

                    rate of heart beat, constriction of blood vessels, hypertension and endocrine

                    stimulation, continuous noise stress conditions adversely affect brain,

                    heart, liver, blood cell count and immunity leading to pathological and

                    behavioural problems (Kryter, 1970). Simmons (1 974) has described the

                    disturbances caused by the shock sound waves to wild birds and domestic

                    animals. The effect of noise on endocrine function and hormones have

                    been studied by Armario et al. (1984), Bailey el al. (1986) and Boer

                    er at. (1989).


                    Pressure

                                   Hypobaria, characteristic of elevated altitude and hyperbaria

                    of the deep sea are stressful conditions caused by the pressure variations.

                    The effects of high pressure on biological systems have been studied and

                    compensations against the deleterious effects of high pressure are best

                    illustrated by the a d a p t ~ v eproperties of 'barophilic' enzymes like

                    fructose-di-phosphatase and pyruvate kinase i n benth~cmarine teleosts

                    (Das, 1986). Altitudin31 stress has attracted the attention of mammalian


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   physiologists interested in adaptive c h a n g e s in respiratory a n d

                   c~rculatoryfunctions of man and other mammals in high altitudes (Hill,

                   1976).


                   Chemrcal Stressors

                                  Chemical stress constitutes the ill effects produced when organisms

                   are exposed to various chemicals. In a way, all chemical pollutants are

                   chemical stressors. Harmful effects of insecticides and detergents in aquatic

                   forms have been investigated (Matsumara et a ] . , 1972; Walsh, 1983;

                   Chattopadhyay and Kumar, 1984). Effects of heavy metals on organisms

                   is another area that has received wide attention (Kumada et a l . , 1980;

                   Pillai, 1983; Cyriac e l a/.,1989). Molecular level studies on chemical

                   stress have l e d t o the report o f t h e production o f a s t r e s s

                   protein in bovine pulmonary artery endothelial cells by sodium arsenite

                   (Deneke, 1992). Salzman and Bowman (1 992) identified another stress

                   protein related to the regulation of prostaglandin production induced by

                   sodium arsenite. It was found that salt stress activates specific genes

                   and consequently enzymes in plants (Cushman et a1 ., 1989; Cushman,

                   1992; Vernon and Bohnert, 1992)


                   Other Physico-chernrcal Stressors

                                  Osmotic stress, ionic stress, pH stress, drought stress and

                   starvation stress responses have been described in various animals by


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   different investigators which have been reviewed by Das (1 986). Osmotic

                   and ionic changes in the aquatic environment affect the physiological

                   mechanisms and energetics o f osmoregulation in aquatic animals. Non-

                   availability of water or drought stress and evaporative loss of water adversely

                   affect terrestrial animals living in arid regions. Changes in the pH of

                   freshwater b o d e s due to the discharge of industrial effluents create problems

                   to aquatic populations. Starvation and malnutrition have also been considered

                   as potent stresses of man and other animals.


                   Social Stressors

                                  Social stress refers to the physiological stress induced by

                   conspecifics due to high density o f population that would lead to

                   aggressive and other behaviours causing increased mortality and decreased

                   reproductive output (Christian, 1961). On the other hand, isolated conditions

                   in social species can also produce variety of behavioural abnormalities

                   like aggression as noted in rodents (Goldsmith et a l . , 1976) and tethered

                   sows (Barnett et a l . , 1987). Abnormal sexual behaviour i s another

                   consequence observed among domestic animals reared in isolation (Beilharz,

                   1985; Price, 1985). Barnett (1 964) has described the physiological changes

                   to restore the delicate balance of the body's metabolism when it has been

                   upset and observed that a wild rat under chronic social stress becomes

                   weak and dies. It has been found that population density induces changes


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   in adrenal weights and over stimulation and exhaustion of the adrenal

                   gland cause fatal effects in crowded population (Christian, 1961, 1963).

                   Social stress leads to retarded gonadal function, excessive adrenal stimulation

                   and exhaustion, decline in thyroid activity, metabolic changes and pathological

                   conditions (Archer, 1979).


                   C.    Stress: Biochemical and Haematological Aspects

                                  Animals adapt to milieu exterieur by internal biochemical

                   adjustments involving the macromolecular components of cells or body

                   fluids and microenvironment within which macromolecules function

                   (Hochachka and Somero, 1984). T h e distribution patterns o f t h e

                   macromolecules i n tissues and organs are functionally related and hence

                   significant in adaptation. Concentrations of macromolecules like enzymes

                   and hormones may be altered in adaptive ways in the respective tissues

                   in response to stress, which will have its bearing on the various metabolites,

                   cell types and organs (Lazarus and Folkman, 1984).


                   Glycogen and Glucose

                                  Among metabolites, glycogen i s of special significance as it is

                   the only storage form of carbohydrate in animals and found primarily in

                   liver and muscle where it generally occurs at about 3-6% and about 0.5%

                   respectively (Kaneko, 1989). Glycogen is a polysaccharide comprised solely

                   of a-D-glucose units linked together through carbon atoms 1 and 4 or


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    I and 6. The absorbed hexoses from the intestine are converted to glucose

                   by the liver and enter the general circulation; the excess are stored as

                   glycogen or as fat. The synthesis of glycogen (glycogenesis) taking place

                   in the liver i s a unidirectional process and i s promoted by insulin. The

                   breakdown of liver glycogen to glucose (glycogenolysis) is through the

                   action of hormones. epinephrine on liver and muscle glycogen, and of

                   glucagon on liver glycogen only. Glucocorticoids promote liver glycogen

                   storage by the enhancement of gluconeogenesis (Granner, 1993a). Thyroxine

                   is found to render the liver more sensitive to the action of epinephrine,

                   resulting in enhanced glycogenolysis (Kaneko, 1989). Animals under stress

                   exhibit biochemical changes associated with glycogen metabolism in muscle

                   and liver (Fink, et al., 1975; Hails, 1978; Mickwitz, 1982; Kozlowski,

                   et al., 1985; Nielsen, 1994). Effect of thermal acclimation on liver and

                   muscle glycogen (Koskella and Pasanen, 1974) and adaptation related

                   to glycogen consequent of exercise (Lamb et al., 1969; Baldwin et al.,

                   1974; Parker and George, 1975) have been investigated.

                                  Glucose is the most readily available energy source continuously

                   given to all tissues by the blood. The continuous source o f blood glucose

                                                          derived from glycogenolysis and
                   is the hydrolysis of gl~~cose-6-phosphate

                   other precursors in the liver, kidney and intestine. Blood glucose level

                   thus depends on the relative rates of glucose production by liver, kidney

                   and intestine, glucose absorption from the gut and glucose utilization by

Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                  all tissues. Liver and muscle tlssues assimilate glucose more rapidly. Higher

                  levels of blood glucose favours formation of glycogen and triglycerols

                  especially in liver and adipose tissue (Kaneko, 1989).

                                 Several hormones a r e established to be involved in the

                  regulations of blood glucose levels (Smith et al., 1983; Granner, 1993b).

                  Insulin helps in the transport of glucose from the extra to the intracellular

                  space and enhances the synthesis of glycogen, thus lowers the blood

                  glucose level.           Hormones like somatostatin (growth hormone) and

                  adrenocorticotropin                 t e n d to elevate blood glucose as t h e y   are

                  antagonistic to the action of insulin. Similarly pancreatic glucagon and

                  epinephrine of adrenal medulla rapidly increase blood glucose. Adrenal

                  corticosteroids also raise blood glucose levels, but their effects are slower

                  and more prolonged.

                                 Blood glucose level has been taken as an indicator for the study

                  of stress responses. When the ambient temperature is raised during

                  exercise, hyperglycemia i s produced which i s caused by an increase in

                  liver glucose output (Hargreaves et al., 1996). Widnell et al. (1990)

                  have observed that cellular stress like hyperthermia induces a greater

                  uptake of glucose consequent to stress induced.insulin-like distribution

                  of certain membrane proteins. In rats, specific physical and chemical

                  stressors could elevate blood glucose levels (hyperglycemia) following

                  the secretion o f t h e adrenal medullary and cortical hormones, but


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    prolonged          e x p o s u r e to      stress reduced        blood   g l u c o s e levels

                    (Mason, 1975; Natelson et al., 1977; Gartner et a / . , 1980; Quirce and

                   Manickel, 1981).


                    Total Lipids

                                  Lipids are basic biochemical components which are not only

                   one of the major fuel reserves of the animal tissues, but also function as

                   important structural component o f membrane systems. Absorbed from

                   the diet, o r synthesized by the liver a n d adipose tissue, lipids are

                   transported between the various tissues and organs for storage. Lipids

                   being a potential energy reserve, are needed by the active tissues like

                   flight muscles. The concentration of lipids is influenced by the conversion

                   of the excess carbohydrate into fat (Schmidt- Nielsen, 1979). It has been

                   found that there i s a substantial accumulation and depletion of lipids in

                   active flight muscles corresponding to activity (George and Berger, 1966;

                   Hochachka and Somero, 1973). As liver, muscle and adipose tissue are

                   closely associated with thermogenesis and temperature adaptation, the

                   role and distribution of fat have special significance (Schmidt-Nielsen,

                   1979; Bartholomew, 1982; Hochachka and Somero, 1984). There are

                   several reports on the effects of stressful conditions like fasting and strenuous

                   exercise on muscle lipids (Morgan, et al., 1969; Vallyathan et al., 1969;

                   Holloszy and Booth, 1976).


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                  Ascorbic acid

                                 Ascorbic acid or Vitamin C is another important molecule which

                  can exercise significant influence on biological activities and hence has

                  been studied in relation to stress (Selye, 1950; Kutsky, 1973; Lewin.

                   1976; Chinoy, 1978; Glickman and Lam, 1992). Man and other primates.

                  guinea pigs, Indian giant fruit eating bat (Pteropus medius), In&an pipistrelle

                  (Vesperugo abramus), some species of birds and fishes are unable to synthesize

                  this vitamin, whereas it is synthesized in the liver of most species and in

                  the kidneys of amphibians and reptiles (Chatterjee, 1970, Chaterjee

                  et al., 1975; Lewin, 1976; Swenson and Reece, 1993). In species which

                  require a dietary source, ascorbic acid is absorbed in the small intestine.

                                 Ascorbic a c ~ dexerts its effect on physiological activities in

                  various ways as reported by GouId (1963), Oser (1965), Prasad (1971),

                  Slitlcin (l971), Bielski and Richter, (1975), Lewin, (1976), Chinoy (1978).

                  Sapper et al. (1 982), Englard and Seifer (1 986), Kaneko (1 989), McDowell

                  (1989), Chatterjee and Nandi ( 1 991), Swenson and Reece (1993), Garrett

                  and Grisham (1995). Ascorbic acid is a strong reducing agent with a

                  general importance as an antioxidant and as a free radical inhibitor, and

                  is also involved in oxidation-reduction reactions in biological systems.

                  In addition, i t is found to influence the levels of cyclic nucleotides,

                  CAMPand cGMP, and enzyme activity. Ascorbic acid takes part in production

                  of hormones such as adrenaline, noradrenaline and serotonin, influences


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    enzyme biosynthesis, associates with detoxicating and antihistaminic activities.

                    It is also concerned with phagocytosis, collagen formation, fibrogenesis

                    and tissue repair activities. Recently it was shown by Mahmoodian

                    el al. ( 1996) that serum and bone alkaline phosphatase activity is decreased

                    during ascorbic acid deficiency.

                                   T h e r o l e o f ascorbic a c i d in overcoming stress i n d u c e d

                    physiological c o n d i t i o n s a r e well known (Selye, 1950) a n d it i s

                    recognized as an anti-stress factor (Kutsky, 1973). Studies have shown

                    that a variety of stress conditions, such as, administration o f vaccines,

                    toxoids, starvation and physical stress, induced blindness, vasoligation

                    and post-surgical stress cause alterations in normal physiology of the

                    a n ~ m a lleading to enhanced utilization and mobilization of Vitamin C

                    (Chinoy, 1978). The increased adrenal cortical steroid output in stress

                    mechanisms i s also correlated with the high turn over of ascorbic acid

                    (Selye, 1950; Szent -Gyorgyi, 1957; Lewin, 1976). Ascorbic acid is oxidlzed

                    by free radicals under light stress in the eye, and has been employed as

                    a useful indicator for quantifying the production of free radicals during

                    photooxidative stress (Glickman and Lam, 1992).


                    Alkalrne Phosphatase and Acid Phosphatase

                                   Enzymes are integral part of physiological adjustments. Among

                    them t w o g r o u p s o f isoenzymes, alkaline phosphatases a n d acid



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    phosphatases, which were first recognized to have clinical significance

                    related to bone and liver diseases, have also been used as indicators to

                    study the physiological state o f specific organs under adverse conditions

                    (Stigbrand et a ] . , 1984). Alkaline phosphatases are a group of isoforms

                    of non-specific enzymes which hydrolyze monophosphoric acid esters at

                    an alkaline pH o f about                     10. They play a role in differentiation,

                    formation of fibrous protein, calcification o f bone and formation of

                    mucopolysaccharide forming ground substance (Simkiss, 1964; Stigbrand

                    et a / . ,1984), carbohydrate metabolism (Burstone. 1962). phosphate transfer

                    in DNA metabolism (Rogers, 1960; Peterson, 1989) and permeability of

                    ATP dependent membrane "pumps" involved in                           t h e passage of

                    metabolites across cell membrane (Simkiss, 1964; Kramer, 1989).

                    In addition to serum, alkaline phosphatase isoenzymes are present in

                    various tissues, especially in bone, kidney, liver, intestine, placenta and

                    other organs o f man a n d other animals; elevated levels o f t h e

                    enzyme is noted in specific ailments (Kaplowitz, et al., 1982; Cornelius,

                    1989; Loeb, 1989). Sukhanuva, et a/., (1 996) has reported the difference

                    in alkaline phosphatase activity in two strains of Drosophila virilis in

                    response io heat stress.

                                   The acid phosphatases, a class of non- specific phosphomono-

                    estarases, hydrolyse esters of monophosphoric acid at acidic pH. The




Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   approximate optimum pH of the enzyme is 5. According to the site of its

                   localization and characteristics of the cell, acid phosphatases are found

                   to be involved in a variety o f cellular activities such a s cellular

                   phagocytosis (Klochars and Wagelius, 1969), dissociation o f tissue

                   components (Weber and Niehus, 1961), protein synthesis (Pearse, 1968),

                   differentiation (Ghiretti,                   1960), absorption (Straus,   1964) and

                   phosphorylation (Stetten, 1964). The activity of acid phosphatases i s

                   especially noticeable in certain pathological conditions (Henry et al.,

                    1974).


                   Stress and Blood Cells

                                  Haematological factors reflect the physiological status of each

                   individual. Blood parameters like the RBC count, WBC count, differential

                   count, packed cell volume (PCV) and dissolved plasma components are

                   widely used to study the internal physiological status of the organism

                   (Daice and Lewis, 1984; Dodds, 1989; Zinkl, 1989; Harris, 1991; Brown,

                    1993; Rodack, 1994; Guyton and Hall, 1996). The effect of heat stress

                   on leukocyte count in domestic fowl has been noted by Nathan et al.,

                   (1 976) and Trout and Mashaly (1994). According to Elvinger e t al. (1991)

                   the total leukocyte counts were higher in heat stressed cows. However,

                   Steplewski and Vogel ( 1 986) have reported that in rats exposed to restraint

                   stress, total leukocytes and lymphocytes were significantly decreased, and



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    neutrophils were markedly increased. Albino rats exposed to acute noise

                    stress showed an elevated level of plasma corticosterone along with reduction

                    in total leukocyte count, increase in neutrophils and reduction in eosinophils

                    and lymphocytes (Sembulingam, et a l . , 1996). Joseph et al. (1991) reported

                    a decrease in WBC count of heat stressed albino rats. Erythrocytes are

                    found to be haemolysed in vitro under heat stress and the extent of damage

                    depends on the duration of the stress (Utoh and Harasaki, 1992). Keatinge

                    et al. ( 1 986) observed increased platelets and red cell counts during early

                    stages of heat stress.


                    Stress and Respiratory Pigments (Haemoglobin and Myoglobin)

                                   Haemoglobin, the respiratory pigment present in the erythrocytes

                    of vertebrates serves the purpose of combining with oxygen in the lungs

                    and readily releasing this oxygen in the tissue capillaries where the

                    gaseous tension of oxygen is much lower than in the lungs. Haemoglobin

                    content is a good measure of the oxygen carrying capacity of the blood

                    and hence of vital importance (Smith et a l . , 1983; Guyton and Hall, 1996).

                    Under hypoxia stress and i n high altitude acclimatization, an increased

                   haemoglobin content and haematocrit are noted (White, 1982; Guyton

                   and Hall, 1996). It has also been reported that increase in ambient temperature

                    affects haemoglobin level and total cell volume in vertebrates (Hensel et

                   at., 1973; Cossins and Bowler, 1987).



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                                    Myoglobin, the muscle respiratory pigment plays a salient role

                     in the functioning of muscle, especially in the red skeletal and cardiac

                     muscles of vertebrates (Torri, 1989). Myoglobin has a very high affinity

                     for oxygen a n d s e r v e s not only a s an o x y g e n storage depot, but

                     facilitates its rapid transfer from the blood capillaries to the oxidizing enzymes

                     of mitochondria (W~ttenberg al., 1975; Turner and Butler, 1988). Wittenberg
                                               et

                     et al. (1975) had reported that the presence of high concentration of

                     t h i s chromoprotein i n skeletal muscle i s usually a s s o c i a t e d with

                     their prolonged activity. It has been shown that a daily programme of

                     strenuous exercise on a treadmill enhanced the myoglobin content in the

                     skeletal muscle of rats (Hagler et al., 1980). Samuel and Alexander(l995)

                     had reported an elevation in myocardial myoglobin levels in exercised

                     rats. Further, inactivity acts as a stimulus for degradation and suppression

                     of tissue myoglobin levels (Catlett et al., 1978). Apart fiom activity, altitudlnal

                     hypoxia has also been reported to be a factor for increasing myoglobin

                     level as opined by Tappan and Reynafarje ( I 957) in the skeletal and cardiac

                     muscle of guinea pigs kept at high altitude.


                     D.    Stress Effect on Organs - Adrenal glands, Spleen and Testis

                                    Increased adrenocortical activity leads to hypertrophy and increase

                     in the weight of the adrenal glands in monkeys (Hayama 1966; Shively

                     and Kaplan, 1984), mice (Davis and Christian, 1957) and albino rats



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   (Sembulingam et al., 1996). Archer (1979)

                   in rodents subjected to stress. Spleen is also found to be sensitive to

                   stress conditions as it has been found that sympathetic stimulation of

                    spleen causes the release of stored erythrocytes and lymphocytes resulting

                    in a reduction in spleenic weight (Milrsh and Rasmussen, 1960; Sembulingam

                    et al., 1996; Guyton and Hall, 1996). Moreover, organ weight -body weight

                    ratio has been used as a parameter to study the general activity pattern of

                    specific organs of animals exposed to stress (Marsh and Rasmussen., 1960;

                    Broom and Johnson, 1993).

                                   Stressors like temperature and light can affect gonads and

                   reproduction in animals. In mammals, it has been found that elevated

                   temperature can result in an inhibition of spermatogenesis, degeneration

                   of seminiferous tubules and sterility (Hensel et al., 1973). Similar

                   observations were made in other animal groups subjected to thermal

                   stress by Brock (1985). It was also reported that during development,

                   towards higher thermal limits, percentage of abnormal embryos increases

                   (Cossins and Bowler, 1987). Light, through photoperiod, influences the

                   gonadai function and reproductive activity. Gonadal activity and the

                   reproductive cycle in mammals are related to the photoperiod by the

                   mediation of the pineal gland (Reiter, 1978, 1987; Pevet et al., 1977).

                   Scharrer ( I 970) suggested that the photic stimuli are converted into chemical



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                   messages by the neurosecretory cells of the hypothalamus which influence

                   the pituitary and subsequent degenerative changes in testis and inhibition

                   of ovarian function. Excessive light stimulus is found to produce degenerative

                   changes in testis and inhibition of ovarian function (Reiter, 1987).


                   E.     Relevance of Chiropteran Study

                                  Mammals. the most highly evolved among vertebrates, have

                   structural a n d physiological adaptations for life in almost every

                   environment on earth that supports life.                          T h e diversified a d a p t i v e

                   features of these homeothermic tetrapods, with a more advanced brain

                   and intelligence, had the long history from the Mesozoic when the threshold

                   had been crossed from reptile to mammal (Romer and Parsons, 1977;

                   Colbert, 1980; Young, 1981). They have undergone adaptive radiation

                   for life in different habitats. Chiroptera are an extraordinary and unique

                   group of mammals who mastered flight at least 55 million years ago,

                   long before man's lineage began. Collectively called bats, these highly

                   specialized true flying mammals evolved with an adaptive radiation that

                   was clearly advantageous accounting for their survival and abundance.

                   The opportunities presented by the flight, nocturnal habit, availability of

                   insects, tropical fruits and flowers led to the astonishing diversity of bats.

                   The order Chiroptera with about 950 species (Hill and Smith, 1986) stands

                   second only to rodents in number of species among mammals, and are



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                     widely hstributed. Their nocturnal habit, and sometimes the related mythical

                     stories, evoked superstitions and aversions which have kept bats alienated

                     from man (Allen, 1939; Peterson, 1964). Possibly these are the reasons

                     why they were not subjected to experimental studies like many other

                     smaller mammals. But the growing awareness of the biology of bats,

                     their role in nature and the relation to man, have stimulated investigations

                     all over the world.

                                    Bats are excellent agents of seed dispersal of fruit trees, and

                     the nectar feeding bats act as pollinating agents. The insect population is

                     brought under check to some extent by insectivorous bats, as a single bat

                     consumes about 2500 to 30J0 insects each night (Gopalakrishana and

                     Sandhu, 1984).              Further, studies on bats have contributed to the

                     development of navigational aids for the blind (Constantine, 1970;

                     Chandrashekaran, 1980), birth control and artificial insemination

                     methods (Gopalakrishna and Sandhu, 1984) and for testing drugs,

                     vaccine production and as experimental animals in stressful conditions

                     (Constantine, 1970).

                                   Bats are a group of mammals bestowed with several interesting

                    features. The specialized features of bats not only include their flight

                    adaptations but also the physiological adaptations to diurnal dormancy

                    and nocturnal activity. Adaptations for true flight in bats are associated




Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                 with a wide array of anatomical, physiological and aerodynamic factors

                 (Vaughan, 1970; Norberg, 1970; Findley et a / . ,1972 ). There are similarities

                 as well as contrasts between birds and bats with respect to anatomical

                 and aerodynamic adaptations for flight; comparable relations also exists

                 with regards to their physiological adaptations for aerial locomotion (Hill

                 and Smith, 1986). Being highly specialized in several respects bats are

                 excellent models of stress physiological studies.

                                The adaptations of bats are worth emphasizing in relation to

                 the influence of stress. Heart rates become high to cope up with the

                 oxygen demand resulting from high metabolic requirements as studied in

                 Phyllostomus hastatus and Pteropus gouldii (Thomas, 1975). Although

                 birds and bats have comparable rates of oxygen consumption and heart

                 rate during flight, bats have increased ability for oxygen transport, and

                 i n the above two species of bats it is accomplished by a higher percentage

                 of red blood cells in the blood i.e., high haematocrit. In Phyllostomus

                 hastatus, oxygen capacity of blood is 40 to 50 per cent higher than that

                 of either a typical bird or non-flying mammal. Hibernating bats have

                 the ability to regulate their haematocrit by storing red blood cells in the

                 spleen during periods of non-activity (Davis, 1970; Hill and Smith, 1986).

                 Ilowever i t is doubtful whether bats can regulate their haematocrit

                 between and during f l ~ g h tsorties. The number and size of RBC and



Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                    WBC of bats are comparable to those reported for other small mammals

                    (Quay and Reeder, 1954; Kallen, 1960; Andrew, 1965; Riedesel, 1977).

                    There is wide range in blood cell counts, especially of RBC, in the members

                    of the same species and a greater variation between fruit eating and

                     insectivorous bats, which may be correlated with temperature regulation

                     and body size (Valdivieso and Tamsitt, 1971).

                                    Energy metabolism of any animal including Chiroptera is of

                     significance in response to stress. The energy to do the mechanical work

                     is derived from the oxidation of either carbohydrate or fat (Thomas, 1975,

                     1980; Thomas and Suthers, 1972; Armstrong et a l . , 1977). Data on

                     Phyllostom~rshastatus by Thomas (1975) suggest a high reliance on

                     carbohydrates where flight sorties observed were of short duration and

                     hence depended only on carbohydrate metabolism. Rhinolophus megaphyllus

                     and Miniopterus schreibersii, both with wings of low or moderately low

                     aspect ratios making                  short dashing flights, appear to depend on

                    carbohydrate anaerobic metabolism, whereas Tadarida australis, Tadarida

                    planiceps, with relatively high aspect wings and making prolonged flight,

                    seem to favour aerobic fat metabolism. Species like Chalinolobus gouldzi

                    and Nyctophilus geoffroj.i, with wings of intermediate aspect ratios, are

                    also intermediate in their preference of anaerobic or aerobic metabolism

                    (Hill and Smith, 1986).




Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                                       As per surface/volume rule or ratio, smaller mammals will lose

                        or gain heat at a higher rate than larger ones, and hence the former will

                        have higher metabolic rate and intake of food per unit of body weight.

                         Thus, a small bat, such as the Little Brown bat, Myotis lucifugus (7-Sg)

                         has a higher daily energy budget compared to that of the large sized American

                         False Vampire, Vampyrum spectrum (170-180g) (Hill and Smith, 1986).

                                        Infomation on the thermal regulatory abilities of megachiropterans
                         were based on large flying foxes such as Pteropus and Rousettus.

                         Vasodilation of wings, ears, scrotum and other exposed areas have been

                         observed when subjected to'a higher temperature for all megachiropterans

                         which also extend their wings under heat stress and the majority

                         maintain an air current by gentle fanning (Lyman, 1970). At low

                         temperature they hold their wings tightly around the body tucking their

                         heads inside; then they decrease the thermal conductance by trapping air

                         in an insulative dead air space in the fur (Hill and Smith, 1986). When the

                         ambient temperature is near to the upper lethal limits, the Megachiroptera

                         increase their respiratory rate and tilay actually pant evaporating more

                        water from the mucous membrane of the mouth and upper respiratory

                        tract. Most megachiropterans actively salivate under conditions of heat

                        stress, to wet the body by licking. and forms like Rousettus aegyptiaclts

                        extends its tongue increasing the evaporative wet surface (Lyman, 1970).

                        The adaptive pattern also shows circadian variations depending on the


Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                 day-night temperatures. Lyman ( 1 970) has described the great variation

                 in temperature regulation in Microchiroptera with considerable species

                 diversity. In many cases they share the regulatory physiological mechanisms

                 of megachiropterans; however variations exist basedon the body size, metabolic

                 rate, roosting habits and hibernation.

                                Thus it may be summarized that uncongenial external stimuli,

                 whether physical, chemical or biological, evoke responses from all animals.

                 The contemporary world with its rapid technological advancements coupled

                 with drastic environmental changes put forth numerous physical, chemical

                 and biological stimuli which can unhesitatingly be considered as stressors.

                 Added on to this is the exobiological challenges and opportunities which

                 emphasize the need for stress physiological studies. The mode and quantum

                 of animal's response to stressful situations depend on the phylogenetic

                 status, climatological influences and degree of adaptations. The available

                 information on stress and its impact are based mainly on rodents. Attention

                 has also been given to farm animals and primates including man. However,

                 information regarding stress physiology of highly specialized mammals

                 are lacking. Hence, the present study on stress physiology of Chiroptera

                 was undertaken with the hope that it would yield valuable information

                 regarding the stress response of this specialized animal group. It is also

                 humbly hoped that the data obtained from this study would have applied

                 relevance to man.

Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam
                                       The bat selected for the present investigation is the Indian

                    dog-faced fruit bat, Cynopterus sphinx (Vahl 1797), belonging to the family

                    Pteropodidae of the suborder Megachiroptera (Hill and Smith ,1986).

                    It is a widely distributed species in the Indian peninsula. Their distribution

                    and taxonomic features have been described by Brosset (1962). Like

                    many fruit bats, Cynopterus sphinx is an arboreal species and appears to

                    have a preference for palm trees. It conceals itself among the leaves

                    during the daytime and the roosts are difficult to find. Other trees like

                    Banyans, Ficus etc., are also used, particularly when suitable palm trees

                    are not available in the vicinity. During night, the time of their foraging,

                    they have been reported to be on trees with ripening fruits in dense forests,

                    in cultivated zones and urban areas. They take to wing early in the evening,

                    well before it is dark, and may feed in groups on the same fruit trees, but

                    visits the flowers solitarily (Brosset, 1962).




Prepared by BeeHive Digital Concepts Cochin for Mahatma Gandhi University Kottayam

				
DOCUMENT INFO