-2-Oxothiazolidine-4-Carboxylic Acid Prevents Endotoxin-induced by steepslope9876


									                               Acid Prevents
Endotoxin-induced Cardiac Dysfunction
Pulmonary Research Laboratory, St. Paul’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada;
and Transcend Therapeutics, Inc., Cambridge, Massachusetts

               We tested the hypothesis that treatment with the glutathione repleting agent, L-2-oxothiazolidine-
               4-carboxylic acid (OTZ), could prevent endotoxin-induced ventricular dysfunction. Rabbits were
               treated with OTZ 2.4 g/kg (10% solution subcutaneously), or an equal volume and osmolality of sa-
               line, 24 h prior to, and again (intravenously) just prior to, infusion of 1 mg/kg E. coli endotoxin (or ve-
               hicle control). Ventricular contractility was measured in isolated hearts perfused by support rabbits.
               Contractility did not change in control groups (Saline/Control [n 7] or OTZ/Control [n 7]) over 6 h.
               However, Emax decreased in the Saline/Endotoxin group ( 16.1              4.5% from baseline, n     7, p
               0.05) and this was prevented by pretreatment with OTZ in the OTZ/ Endotoxin group ( 6.3 4.1%,
               n 7, p 0.05 by analysis of variance). To better understand the mechanism of this effect we mea-
               sured myocardial glutathione concentration and found it to be greater in OTZ/Endotoxin animals
               (104 4 ng/g) than in the Saline/Endotoxin animals (80 3 ng/g, p 0.05). OTZ did not apprecia-
               bly alter the endotoxin-induced increase in serum concentration of tumor necrosis factor (TNF) or
               the endotoxin-induced increase in myocardial leukocyte content. We conclude that oxygen radicals
               contribute to the early decrease in left ventricular contractility after endotoxin infusion and this de-
               crease may be prevented by OTZ. Poon BY, Goddard CM, Leaf CD, Russell JA, Walley KR. L-2-
               oxothiazolidine-4-carboxylic acid prevents endotoxin-induced cardiac dysfunction.
                                                                                              AM J RESPIR CRIT CARE MED 1998;158:1109–1113.

When cardiovascular dysfunction complicates sepsis, the mor-                     ute to ventricular dysfunction during sepsis is not known.
tality rate approximately doubles (1, 2), contributing to the                    However, release of reactive oxygen radicals by leukocytes is
high and rising incidence of death due to serious infections.                    an important contributor to the pathogenesis of ischemia-rep-
An important aspect of cardiovascular dysfunction of sepsis is                   erfusion injury in the heart (12–14). Thus, it is reasonable to
decreased left ventricular function (3). A number of compo-                      postulate that oxygen radicals may be important in causing
nents of the septic inflammatory cascade have been shown to                      ventricular dysfunction in sepsis.
contribute to decreased ventricular function, including tumor                        Glutathione (GSH) is an important endogenous antioxidant
necrosis factor (TNF) (4, 5), other proinflammatory cytokines                    that protects cells and tissues against oxygen radical damage
(6), and leukocytes (7). TNF and other proinflammatory cy-                       (15–17). Continued release of oxygen radicals during sepsis
tokines may mediate part of their effect via nitric oxide (NO),                  depletes the supply of glutathione, leaving tissues vulnerable
either via NO’s effect of myocyte cyclic guanosine 3 ,5 -mono-                   to damage by oxygen radicals (9). Restoring glutathione con-
phosphate (cyclic GMP) or via peroxynitrite formed by com-                       centrations is necessary to continue its protective role, but in-
bination of NO with oxygen radicals (8). Leukocytes also me-                     creasing glutathione levels can be problematic. Direct admin-
diate some of their damaging effects in other tissues via                        istration of glutathione is restricted because glutathione is easily
oxygen radical formation (9). Whether oxygen radicals gener-                     oxidized and hydrolyzed by intestinal and hepatic -glutamyl-
ated by myocytes, leukocytes (10, 11), or other cells, contrib-                  transferase (18). The rate of glutathione synthesis is usually
                                                                                 limited by the amount of cysteine present (15). Cysteine, a
                                                                                 glutathione precursor, is rapidly oxidized, has limited cell up-
(Received in original form February 12, 1997 and in revised form May 20, 1998)
                                                                                 take, and may be toxic when present extracellularly at high
Supported by Transcend Therapeutics, Inc. and the Medical Research Council of
                                                                                 concentrations (19, 20). However, glutathione repletion can
                                                                                 be achieved effectively by administering L-2-oxothiazolidine-
Christopher Goddard is a Fellow of the Heart and Stroke Foundation of British
Columbia and Yukon.                                                              4-carboxylic acid, OTZ (Procysteine; Transcend Therapeutics,
Keith R. Walley is a Scholar of the Heart and Stroke Foundation of Canada.
                                                                                 Inc., Cambridge, MA) (21). This compound is converted to
                                                                                 cysteine by the intracellular enzyme, oxoprolinase (22).
Correspondence and requests for reprints should be addressed to Keith R.
Walley, M.D., U.B.C. Pulmonary Research Laboratory, St. Paul’s Hospital, 1081        Accordingly, we asked if OTZ could prevent decreased
Burrard Street, Vancouver, BC, V6Z 1Y6 Canada.                                   ventricular contractility observed after endotoxin infusion (5,
Am J Respir Crit Care Med Vol 158. pp 1109–1113, 1998                            23). We reasoned that OTZ would replenish depleted glu-
Internet address: www.atsjournals.org                                            tathione stores and enable the glutathione cycle to catabolize
1110                                                     AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE                VOL 158    1998

oxygen radicals. To address our hypothesis we used an iso-                  with normal saline via the Millar catheter lumen until a left ventricu-
lated heart perfused by a support rabbit (7, 23). Endotoxin in-             lar end-diastolic pressure of 4 mm Hg was achieved (volume approxi-
fusion into the support rabbit provided a whole animal model                mately 200 l). After the ventricular balloon and pacing electrodes
of sepsis while the isolated heart allowed us to control coro-              were in place, the isolated heart was then allowed to beat isovolumi-
                                                                            cally for 15 min.
nary perfusion pressure, preload, afterload, heart rate, and
eliminate mechanical interaction of the heart with surround-                Measurement of Left Ventricular Function
ing structures.
                                                                            Ventricular contractility was measured using the slope of the end-sys-
                                                                            tolic pressure-volume relationship, Emax (24). To calculate Emax, the
METHODS                                                                     intraventricular balloon was inflated using a syringe pump at a con-
                                                                            stant rate of 800 l/min to a maximal volume determined as the vol-
This study was approved by the University of British Columbia Ani-          ume at which cardiac dysrhythmia occurred (approximately 400 l). A
mal Care Committee and adheres to the Canadian guidelines on ani-           constant balloon inflation rate allowed time measurements to be con-
mal experimentation.                                                        verted directly to intraventricular volume measurements. The maxi-
                                                                            mal balloon inflation volume never approached the balloon’s un-
Pretreatment Protocol
                                                                            stressed volume of 3 ml. During inflation, left ventricular pressure was
Fifty-six rabbits (New Zealand White) in the experiments were pre-          sampled at 100 Hz and stored in digital format. The slope of the best-
treated with either a total of 2.4 g/kg of a 10% OTZ solution (OTZ          fit line to the ascending ramp of peak systolic pressures is Emax. Im-
groups), or an equal volume and osmolality of saline (Saline groups),       mediately after inflation to maximal volume, the balloon was deflated
administered in three divided doses subcutaneously at 4-h intervals         to the initial volume of approximately 200 l.
beginning 24 h prior to the experiment.
                                                                            Measurements of Perfusing Blood
Surgical Preparation of the Support Rabbit
                                                                            Arterial PO2, PCO2, and pH were measured using a blood gas analyzer
Twenty-eight of the above rabbits (3.5 0.5 kg) were anesthetized us-        (ABL30 Radiometer, Copenhagen, Denmark). We also measured ar-
ing -chloralose (Sigma, St. Louis, MO) 55 mg/kg and urethane (32%;          terial lactate concentration (YSI 2300 Stat Glucose-Lactate analyzer;
Sigma) 4 ml/kg intravenously. A tracheotomy was performed and the           YSI Incorporated, Yellow Springs, OH) and hemoglobin (IL482 Co-
rabbits were ventilated with room air and supplemental oxygen to            oximeter; Instrumentation Laboratory, Lexington, MA).
maintain PCO2 between 30 to 40 mm Hg and PO2 above 100 mm Hg.
Polyethylene catheters (interior diameter [i.d.] 1.67 mm, outer diame-      Serum TNF Bioassay
ter [o.d.] 2.42 mm; Intramedic, Becton Dickinson, Parsippany, NJ)
were inserted into the right carotid artery and the left external jugular   Serum TNF concentrations were measured using the WEHI bioassay
vein. A third polyethylene catheter (i.d. 1.14 mm, o.d. 1.57 mm) was        (25). Briefly, 5    105 WEHI 164 subclone 13 cells in 100 l were
inserted into the left femoral artery to monitor arterial blood pressure.   added to 100 l volumes of serial dilutions of serum samples, and
Rabbits were anticoagulated with 1,000 IU/kg heparin (Organon;              were incubated overnight. Then cell viability was measured with a col-
Teknika, Toronto, ON, Canada) intravenously. A crystalloid solution         orimetric assay using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazo-
(Plasma-Lyte A, with 7 IU/ml heparin; Baxter Corp., Toronto, ON,            lium bromide (MTT; Sigma). During the final 6 h of the incubations,
Canada) was continuously infused via the left external jugular vein         20 l MTT (5 mg/ml in phosphate-buffered saline) was added to each
catheter. Generally, the animals required 20 to 30 ml crystalloid dur-      sample. Supernatant (150 l) was aspirated from each well and 100 l
ing the surgical preparation of the isolated heart, and an additional 30    acidified isopropanol was added. Absorbance was measured at 550
to 40 ml/h throughout the experimental period. When pH fell below           nm. TNF concentrations in experimental samples were calculated us-
7.35, 5-ml boluses of 6% sodium bicarbonate were given (approxi-            ing a standard curve generated by serial dilutions of recombinant mu-
mately 20 to 30 ml/experiment). A rectal temperature probe was in-          rine TNF- . These bioassays consistently detected TNF concentra-
serted and the core body temperature of the animal was maintained at        tions above 1 pg/ml.
38.9 0.2 C using a heating blanket.
                                                                            Myocardial Leukocyte Content
Langendorff Column and Extracorporeal Circuit                               Immediately after the conclusion of the experiment the blood perfu-
The support rabbit was then connected to a circuit which perfused a         sion circuit was interrupted and normal saline was simultaneously in-
Langendorff column. Arterial blood from the right carotid catheter of       fused into the isolated heart to flush out red blood cells from the myo-
the support rabbit was pumped via a roller pump to an open perfusion        cardial circulation (approximately 5 min). Glutaraldehyde 2.5% in
column connected to a heated heart chamber, to produce a coronary           phosphate buffer was then added to the saline perfusion circuit and
perfusion pressure of 75 mm Hg at the level of the aortic valve of the      the heart was perfusion fixed for 10 min. The isolated heart was then
isolated heart. Blood overflowing from the perfusion column and             removed from the apparatus and transferred to a container of the
venous blood from the isolated heart was pumped back via a second           same fixative. Left ventricular tissue sections (5 mm thickness) from
roller pump through a 40- m blood filter (SQ40S Blood Transfusion           hearts fixed in glutaraldehyde were dehydrated and embedded in par-
filter; Pall Biomedical Products Corporation, East Hills, NY) to the        affin. Serial sections (4 m thickness) were stained with hematoxylin
support animal via the external jugular vein catheter. The total vol-       and eosin. The number of random fields, at 400 original magnifica-
ume of this circuit was approximately 35 ml.                                tion, necessary to count 100 leukocytes in each group was recorded.
                                                                            The average number of leukocytes per field was then determined as a
Surgical Preparation of the Isolated Heart                                  quantitative assessment of myocardial leukocyte content.
The remaining 28 (out of the initial 56) rabbits (2.5     0.5 kg) were
anesthetized with a mixture of ketamine 80 mg/kg and xylazine 5 mg/         Experimental Protocol
kg subcutaneously. A midline sternotomy and pericardiotomy was              On the day of the experiment an additional 2.4 g/kg OTZ 10% solu-
performed. The hearts were rapidly excised and affixed via the aorta        tion (OTZ groups) or equivalent volume of saline (Saline groups) was
to the Langendorff column. The pulmonary artery was incised at the          given intravenously at a rate of 2 ml/min over approximately 40 min
base of the right ventricular outflow tract to allow venous drainage        (21). One hour after the start of OTZ (or saline) infusion, baseline
from the right ventricle. A 5-mm incision was made in the left atrium       measurements were taken and 1 mg/kg endotoxin (lipopolysaccha-
and a 7-French single-lumen pressure transducer (Millar Instruments         ride; Sigma) (Endotoxin groups) or an equivalent volume of vehicle
Inc., Houston, TX) surrounded by a saline-filled latex balloon (un-         (Control groups) was given intravenously over 30 min. These two in-
stressed volume 3 ml) was inserted into the left ventricle and secured      terventions defined four experimental groups which were Saline/En-
using an external ligature surrounding the left atrium. Pacing elec-        dotoxin (n    7) and OTZ/Endotoxin (n       7) to test the hypothesis
trodes were attached to both the left and right atria and the hearts        that OTZ prevents endotoxin-induced ventricular dysfunction, and
were paced at 150 beats/min. The ventricular balloon was inflated           Saline/Control (n 7) and OTZ/Control (n 7) to control for time
Poon, Goddard, Leaf, et al.: Oxygen Radicals and Cardiac Function                                                                        1111

effects and for any independent effects of OTZ. Variables were mea-       statistical comparisons (Saline/Endotoxin versus OTZ/Endo-
sured at baseline and 6 h after the start of endotoxin infusion.          toxin p      0.009, Saline/Endotoxin versus Saline/Control p
                                                                          0.034, or Saline/Endotoxin versus OTZ/Control p 0.005).
Glutathione Assay
                                                                              Serum TNF concentrations increased to the same extent in
In entirely separate experiments from those described previously, rab-    the Saline/Endotoxin and OTZ/Endotoxin groups (Figure 2).
bits were pretreated with OTZ (n 3) or with saline (n 3) and en-          In the control groups that did not receive endotoxin, TNF was
dotoxin was infused, as described. Six hours after the start of endo-
                                                                          initially slightly elevated, probably related to the surgical prep-
toxin infusion, hearts were rapidly excised and snap-frozen in liquid
nitrogen. Glutathione levels were measured in frozen heart tissue us-     aration, and then decreased (Figure 2). Myocardial leukocyte
ing the Bioxytech GSH-400 colorimetric assay (R&D Systems, Min-           content of 1.5 0.2 leukocytes/field in the Saline/Control and
neapolis, MN). Briefly, 500 mg of tissue were homogenized in 10 ml        OTZ/Control groups increased to 2.4 0.2 leukocytes/field in
ice-cold 5% metaphosphoric acid (Sigma). A volume of 100 l of su-         the Saline/Endotoxin and OTZ/Endotoxin groups (p 0.005)
pernatant was then mixed with 800 l buffer (200 mM potassium              (Figure 3). However, OTZ administration had no significant
phosphate, pH 7.8 at 25 C, containing 0.2 mM diethylenetriamine           effect on myocardial leukocyte concentration.
pentaacetic acid and 0.025% lubrol), 50 l each of a solution of 1.2           In separate experiments we found that myocardial glu-
10 2 M chromogenic reagent in 0.2N hydrochloric acid and 30% so-          tathione concentrations were greater in rabbits treated with
dium hydroxide (Bioxytech GSH-400 kit; R&D Systems). After a 10-
                                                                          OTZ (104 4 ng/g) than in those treated with saline (80
min incubation at 25 C, absorbance was measured at 400 nm. Glu-
tathione levels were calculated using a standard curve generated by
                                                                          3 ng/g) (p 0.05) 6 h after the start of the endotoxin infusion.
serial dilutions of glutathione in solution (Sigma).                          There were no differences between groups in blood gas
                                                                          measurements, lactate, or hemoglobin of support rabbit blood
Data Analysis                                                             that perfused the isolated hearts that could account for the
We tested the principal null hypothesis that there was no difference in   measured difference in contractility between the Saline/En-
contractility (Emax) between the four experimental groups at 6 h af-      dotoxin and OTZ/Endotoxin groups (Table 1).
ter the start of endotoxin infusion with a two-way repeated measures
analysis of variance (ANOVA) using p 0.05 as significant. Specifi-        DISCUSSION
cally, when we analyzed the data we included a factor for absence/
presence of OTZ, one for absence/presence of endotoxin, and an in-        These results show that OTZ, a cysteine prodrug and glu-
teraction term between the two. When a significant difference was         tathione repleting agent (16, 21), prevents the early decrease
identified we used a sequentially rejective Bonferroni test procedure     in ventricular contractility in isolated-perfused hearts follow-
to identify specific differences. Similar analysis was used to test for   ing endotoxin infusion into support rabbits. Similar to previ-
differences in other measured variables. Data are reported as mean        ous reports (16, 17, 21, 22), OTZ administration also increased
standard error.                                                           myocardial glutathione concentrations after endotoxin infu-
                                                                          sion. These results support the hypothesis that oxygen radicals
RESULTS                                                                   contribute to the early decrease in ventricular contractility in
Emax decreased by 16.1          4.4% in the Saline/Endotoxin              sepsis.
group (Figure 1) but did not decrease in the OTZ/Endotoxin                   OTZ administration did not alter serum TNF expression or
group ( 6.3 4.1%) by 6 h after the start of endotoxin infu-               the myocardial leukocyte retention that occurred after endo-
sion. Emax did not change significantly from baseline to 6 h in           toxin infusion. One possible explanation is that TNF and oxy-
either of the Saline/Control or OTZ/Control groups (Figure 1).            gen radical effects are unrelated and caused by separate mecha-
The statistical interaction between OTZ and endotoxin was                 nisms. Alternatively, these data suggest that oxygen free
significant (p     0.029) and the Saline/Endotoxin group dif-             radicals, modulated by OTZ, have myocardial depressant ef-
fered from all three other groups after correction for multiple           fects downstream in the septic inflammatory response from

                                                                          Figure 2. Average serum TNF concentrations are shown with stan-
Figure 1. Contractility, as measured by average Emax, is shown at         dard error bars. Endotoxin infusion causes a marked increase in se-
6 h after the start of endotoxin infusion, with standard error bars.      rum TNF concentration (endotoxin effect, p 0.018) but there is
Emax decreases significantly in the Control/Endotoxin group com-          no statistically significant effect of OTZ (p 0.788) and no statisti-
pared with all other groups (*p 0.05, ANOVA). For the key pro-            cally significant interaction between OTZ and endotoxin (p
spectively planned comparison of the Control/Endotoxin to OTZ/            0.402). Standard errors in the Saline/Control group are so small
Endotoxin groups, p 0.007 by ANOVA.                                       the error bars lie within the symbols.
1112                                                             AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE           VOL 158   1998

                                                                                     that oxygen radicals play in septic myocardial dysfunction has
                                                                                     not been determined.
                                                                                         In 1981, Williamson and Meister described OTZ as a cys-
                                                                                     teine delivery system and glutathione enhancer (16). Oxopro-
                                                                                     linase, an enzyme present in most mammalian cells, metabo-
                                                                                     lizes OTZ into cysteine and CO2 at the expense of ATP. OTZ
                                                                                     treatment maintained cellular glutathione levels when gluta-
                                                                                     thione-depleting agents were given to healthy animals (32, 33)
                                                                                     and OTZ repleted tissue glutathione levels in acutely septic
                                                                                     rats (34). In accord with these studies we found that OTZ in-
                                                                                     creased myocardial glutathione concentration, measured 6 h
                                                                                     after endotoxin infusion. Thus, OTZ administration is an in-
                                                                                     tervention that allowed us to test for a possible myocardial de-
                                                                                     pressant effect of oxygen radicals.
                                                                                         Oxygen free radicals come from several sources and could
                                                                                     have several effects in the heart. Activated neutrophils are im-
                                                                                     portant sources of oxygen radicals and activated neutrophils
                                                                                     accumulate in the heart after endotoxin infusion in animal
Figure 3. Average leukocyte count in the myocardium (sampled                         models (7, 10, 11, 23). Filtering leukocytes from coronary blood
immediately after the 6-h time point measurements) per 400                           prevents the early decrease in ventricular contractility after
field is shown for all four groups with standard error bars. ANOVA                   endotoxin infusion in rabbits (7). Because OTZ also pre-
shows that there is a significant endotoxin effect (*p     0.05) but                 vented the early decrease in contractility in a similar experi-
that there is no OTZ effect (p NS).                                                  mental model, it is reasonable to postulate that neutrophils
                                                                                     mediate much of their myocardial depressant effects via oxy-
                                                                                     gen radicals. However, the decrease in contractility is not nec-
proinflammatory cytokines (6) and downstream from leuko-                             essarily due to leukocyte release of oxygen radicals. It is also
cytes, which accumulate in the heart (7, 10, 11, 23) and con-                        possible that leukocytes decrease ventricular contractility by
tribute to the early decrease in ventricular contractility in                        other means, such as cytokine release, and it is conceivable
models of sepsis (7).                                                                that OTZ could have protected cells from other oxidant stress
    Myocardial dysfunction has been reported in human sepsis                         generated within the myocytes. Alternatively, oxygen radicals
(3) and in animal models of sepsis (4, 5, 7, 10, 23). A number                       may decrease contractility via intracellular oxidant signaling
of mechanisms have been identified (26–30). Circulating myo-                         (35) without necessarily damaging tissue (36). OTZ could
cardial depressant factors appear to contribute (26). Proin-                         modify intracellular oxidant signaling (35) and prevent this ef-
flammatory cytokines (6), notably TNF (4, 5, 6, 27), may act as                      fect without altering tissue morphometry.
myocardial depressant factors. These cytokines may mediate                               A number of issues related to the experimental model
part of their effect via NO generation from nearby endothe-                          should be addressed. The decrease in contractility and in-
lium, from cardiac myocytes (8), and from other cellular sources.                    crease in serum TNF concentration observed after endotoxin
NO may mediate its myocardial depressant effects in several                          administration in this model resembles that observed after
ways, including by increasing cyclic GMP activity (28) and also                      acute endotoxin or proinflammatory cytokine administration
by forming peroxynitrite after combining with oxygen radicals                        in other animal models (4, 5, 7, 10, 23) and in acute studies in
(29). The importance of NO is uncertain as other studies do                          humans (37). However, whether this endotoxin infusion model
not show NO-mediated myocardial depression in animal mod-                            in rabbits models the cardiovascular changes over days de-
els of sepsis (30). In addition, other inflammatory mediators                        scribed in human septic shock (3) is not known. Therefore,
(e.g., platelet activating factor [31] ) and leukocytes (7) appear                   these results should be interpreted in this light and limited to
to contribute to myocardial dysfunction in sepsis. The role                          the early decrease in contractility after an initiating septic
                                                                                     stimulus. Differences in contractility between the Saline/En-
                                                                                     dotoxin group and the OTZ/Endotoxin group were indepen-
                                                                                     dent of any changes in myocardial perfusion pressure, pre-
                                                                                     load, afterload, heart rate, and ventricular interaction (4, 24)
                                  TABLE 1                                            because these factors were all kept constant in the isolated-
              MEASUREMENTS OF PERFUSING BLOOD*                                       supported heart where Emax was measured. Similarly, PO2,
                            Saline/      Saline/            OTZ/         OTZ/
                                                                                     PCO2, pH, lactate, and hemoglobin of support rabbit blood
                   Time     Control     Endotoxin          Control     Endotoxin     that perfused the isolated hearts did not account for the mea-
                                                                                     sured difference in contractility between the Saline/Endotoxin
PO2, mm Hg          0     519    16     504       14     450    30     525    13
                                                                                     and OTZ/Endotoxin groups. Although lactate rose with time
                    6     527    14     451       49     534    19     513    16
                                                                                     in support rabbit blood, there was no significant difference be-
PCO2, mm Hg         0     37.6   3.9    39.7      3.6    37.3   2.5    34.6   2.2    tween groups. Thus, the effect of OTZ treatment on endo-
                    6     43.1   2.6    41.6      2.8    34.5   1.1    40.2   1.6
                                                                                     toxin-induced ventricular dysfunction is not accounted for by
pH                  0     7.26   0.04 7.25        0.07 7.33     0.03 7.33     0.02   these differences in perfusing blood.
                    6     7.33   0.03 7.31        0.04 7.37     0.03 7.29     0.01
                                                                                         In summary, OTZ treatment increases myocardial glu-
Lactate, mmol/L     0      2.1   0.4     1.9      0.3     1.9   0.4     2.3   0.7    tathione concentration and prevents the early decrease in con-
                    6      4.7   1.5    12.9      0.9†    8.1   1.6†   10.5   1.1†   tractility after endotoxin infusion, implying that oxygen radi-
Hemoglobin, g/dl    0      9.4   0.8     9.7      0.6     9.9   0.5     9.1   0.2    cals are in part responsible for impaired ventricular function.
                    6      7.4   0.4†    7.5      0.5†    7.9   0.3†    7.1   0.4†   Oxygen radical–mediated ventricular dysfunction may account
 * Values are expressed as mean standard error.                                      for some of the previously observed leukocyte-mediated myo-
   Different from Time 0 baseline, p 0.05.                                           cardial dysfunction after endotoxin infusion (7).
Poon, Goddard, Leaf, et al.: Oxygen Radicals and Cardiac Function                                                                                         1113

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