Effect of Certain Agonists _amp; Antagonists on Isolated Guinea-pig Ileum

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					Effect of Certain Agonists & Antagonists on
          Isolated Guinea-pig Ileum


             Lab #4
                           Objectives

 Discuss the types of receptor present in guinea-pig ileum
 Explain the action of agonists & their specific antagonists
 Discuss the reasons for using guinea-pig ileum
 Explain of effect of different drugs on isolated guinea-pig ileum curve
              Types of receptors in GPI


1- Cholinergic receptors
2- Serotonergic or tryptaminergic receptors (5-HT1→5-HT7)
3- Histaminergic receptors
                   Cholinergic receptors

1- NN R
   Agonist: Dil. Nicotine
   Antagonist: Conc. Nicotine

2- M3 R
   Agonist: Ach
   Antagonist: Atropine
         Serotonergic or tryptaminergic receptors

Serotonin = 5-HT(5-hydroxytryptamine)
5-HT receptors in GPI:
5-HT2A


Agonist: serotonin
Antagonist: ketanserin
               methysergide
               cyproheptadine (blocks 5-HT2A & H1)
                     Histaminergic receptors


   R          Distribution          Action            Agonist          Antagonist
subtype
H1        Smooth               contraction        Histamine         Mepyramine
          muscles                                                   cyproheptadine

H2        Gastric mucosa Gastric acid             Histamine         Cimetidine
                         secretion                                  Ranitidine
H3        Presynaptic          Autoregulation     Histamine         Thioperamide
                               of H release


N.B. Histamine acts by stimulating Gs protein → ↑ cAMP → ↑ [Calcium]ic → contraction
                    Direct acting drugs

 Direct spasmogen

  e.g. Barium chloride

 Direct spasmolytic

  e.g. Papaverine
                     Advantages of GPI



 No myogenic contraction
 More sensitive to histamine
                                                              Experiment




N              W N                                          W+N                                       W+N

                                                                                              0.1ml         0.1ml
       Ach                                          Hist.                                     Bacl2         5-HT
       0.1ml




                                                                                                                    Papaverine 0.1ml
                                                    0.1ml                 Hist. 0.1ml




                                                                                                                                       Bacl2 0.1ml
                 Atropine 0.1ml

                                  Ach 0.1ml




                                                                                                                                                     5-HT 0.1ml
                                              W+N




                                                                                        W+N
                                                              AH 0.2 ml




Key:
Hist.=histamine
AH= antihistamine
5-HT=serotonin
                                                Experiment

  Identification of site of action of an unknown drug using isolated guinea-pig
                                          ileum




                N            W N                                           W+N                                W+N

                     Ach                                           Hist.
                     0.1ml                                         0.1ml




                                                                                         Hist. 0.1ml


                                                                                                       Unk.
                                                Ach 0.1ml
                               Atropine 0.1ml




                                                                             AH 0.2 ml
                                                            Unk.




Key:
Ach= acetylcholine
Hist.=histamine
AH= antihistamine
Unk.= unknown

				
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posted:3/12/2012
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