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1Department of Internal Medicine, College of Medicine, National Taiwan University, National Taiwan University Hospital; and 2Department of Surgery, Municipal Jen-Ai Hospital, Taipei, Taiwan
Submitted 17 May 2002 ; accepted in final form 5 March 2003
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONDISCLOSURESREFERENCES |
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acute myocardial infarction; contraction band necrosis; reperfusion
Connexin43 (Cx43), a phosphoprotein, is the 43-kDa member of a conserved family of membrane spanning gap junction proteins, of which Cx43 is the principal junctional protein in mammalian myocardium (4). Gap junction mediates cell-to-cell movement of Ca2+, which may induce calcium overloading and increase contraction band necrosis during reperfusion (48). Changes in phosphorylation can affect channel function and properties (3). Increased dephosphorylated Cx43 contributes to electrical uncoupling at the gap junction during acute myocardial ischemia (3). Previous studies have demonstrated that traffic of potentially harmful cytosolic messengers such as InsP3 between ischemic cells and surrounding nonischemic cells might cause increased injury (42), leading to myofibrillar hypercontracture and further precipitating cell death (7). Gap junction uncouplers that induced attenuated amounts of Cx43 protein and increased dephosphorylation (22) have been reported to exert a beneficial effect in ischemia-reperfusion models in both the myocardium (16, 17) and the brain (38, 39).
Troglitazone, an antidiabetic thiazolidinedione that enhances insulin sensitivity and a peroxisome proliferator-activated receptor-
agonist (46), has a scavenging effect on reactive oxygen species (25). It possesses structural similarity to certain antioxidants, including 
-tocopherol and probucol. Cominacini et al. (9) showed that under the same stress, troglitazone was much more potent as a radical scavenger than vitamin E. Negasaka et al. (34) showed that troglitazone has an inhibitory effect on peroxidation of human low-density lipoprotein (LDL). Inoue et al. (25) demonstrated that troglitazone can dose dependently transfer electrons directly to cytochrome c and compete for electrons from superoxide with cytochrome c. Free radicals have been reported to modulate the communication of gap junction in some types of cells (20). The aims of the study were 1) to assess the effects on infarct size of troglitazone; 2) to assess whether the cardioprotective effect of troglitazone was associated to quantitative and qualitative changes of Cx43 protein expression; and 3) to test whether free radicals act as a mediator of the effect of troglitazone on Cx43 protein in an ischemia-reperfusion model.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONDISCLOSURESREFERENCES |
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Near the base of the heart, the left anterior descending artery proximal to the first diagonal branch was encircled with a 4-0 silk suture. To measure collateral blood flow at baseline and during ischemia, coronary blood flow was detected by intracoronary Doppler flow wire as previously described (31). All procedures were in accordance with the Guide for the Care and Use of Laboratory Animals (NIH Publication No. 85-23, Revised 1996).
Experimental protocol. The dogs were randomly assigned to one of four groups. All animals were subjected to a 60-min coronary occlusion followed by 120 min of reperfusion. The control group (n = 21) received only vehicle (5 ml saline) before the 60-min occlusion. The treated animals were intravenously administered as a bolus injection before the 60-min occlusion directly with 1, 5, and 50 mg/kg of troglitazone (n = 18, 17, and 17, respectively; Sankyo, Tokyo, Japan). Because Cx43 undergoes rapid postmortem dephosphorylation within minutes of tissue dissection (3), sham operation animals (n = 3) served as internal controls.
Measurements of infarct size. Infarct size was determined as previously described (31) using 1% triphenyltetrazolium chloride (TTC, Sigma Chemical) in phosphate buffer (pH 7.4). Left ventricular area at risk (AAR) and the area of infarcted tissue were assessed in a blinded fashion by two different investigators using computer planimetry. The reported data were expressed as the mean values of the two investigators.
Histology analysis. Extensive histological samples were taken from each transverse section, processed by conventional methods, and stained with hematoxylin and eosin and Masson for contraction band. A pathologist who was unaware of the treatment protocol examined the samples for microscopic evidence of contraction band necrosis on random fields at a magnification of x400. In each case the results from the section with the highest number of bands were used. The histological severity of contraction band necrosis was used to grade injury on a scale of 0 to 3 for the number of contraction bands: 0 (absent), 1 (mild), 2 (moderate), and 3 (severe) as described previously (31). Reproducibility of the method for grading contraction band necrosis was assessed by analyzing interobserver and intraobserver variabilities. Interobserver variability was determined by having a second observer (T.-M. Lee) reanalyze staining from the original preparations analyzed by the first observer. The calculated coefficients of interobserver and intraobserver variations were <9% and 5%, respectively.
Western blot analysis. After being stained with TTC, samples of the left ventricle from the border zone and noninfarcted areas were cut transmurally to include all layers from the epicardium to the endocardium, frozen rapidly in liquid nitrogen, and stored at –80°C until use. Samples were homogenized with a kinametic polytron blender in 100 mM Tris · HCl (pH 7.4) supplemented with 20 mmol/l EDTA, 1 mg/ml pepstatin A, 1 mg/ml antipain, and 1 mmol/l benzamidin. Homogenates were centrifuged at 10,000 g for 30 min to pellet the particulate fractions. The supernatant protein concentration was determined with the BCA protein assay reagent kit (Pierce). Protein (20 µg) was separated by 8% SDS-PAGE and electrotransferred onto a nitrocellulose membrane. After incubation with rabbit polyclonal anti-Cx43 antibodies (Zymed; South San Francisco, CA), the nitrocellulose membrane was then rinsed with a blocking solution and incubated for 2 h at room temperature. The antibody was raised against a segment of the third cytoplasmic domain of rat Cx43 for detection of both phosphorylated and nonphosphorylated forms. Antigen-antibody complexes were detected with 5-bromo-4-chloro-3-indolyl-phosphate and nitroblue tetrazolium chloride (Sigma). Prestained low-molecular-weight markers were used to identify the electrophoretic mobility of Cx43. Films were volume integrated within the linear range of the exposure using a scanning densitometer. Experiments were replicated three times, and results were expressed as the mean value.
Confocal microscopy. To investigate the spatial distribution and quantification of Cx43, analysis of confocal microscopy was performed on the left ventricular muscle from the border zone. Hearts were snap frozen in liquid nitrogen and embedded in OCT compound (Tissue-Tek), and cryosections were performed at a thickness of 5 µm. The slides containing the sectioned tissues were rehydated in 0.01% sodium bicarbonate at pH 7.4. Tissues were incubated with Chemicon anti-Cx43 antibodies at dilution 1:200 in 5% nonfat milk in PBS for 2 h at 37°C. The second antibody was monoclonal goat anti-mouse IgG conjugated to fluorescein isothiocyanate (Sigma) at 1:50 dilution in PBS containing 0.5% BSA for 1 h. The sections were washed three times with PBS and mounted in Dako fluorescent mounting medium. Primary antibody was omitted and run in parallel in negative controls.
Immunolabeled sections were examined through the use of confocal laser scanning microscopy (LSM-410 Invert, Zeiss) at an excitation wavelength of 488 nm. Each transmural section was examined at a low power to determine the overall tissue architecture and amount and distribution of Cx43 label and at a higher power to detect the precise distribution at the cellular level. Each test area was digitized into a 1,024 x 1,024 matrix.
Superoxide anion assays. Serial in vivo blood samples from the great cardiac vein were withdrawn at baseline (15 min after stabilization), 30 min after coronary ligation, immediately before coronary reperfusion, 1, 2, 3, 4, 30, and 60 min after reperfusion, and at the termination of reperfusion (2 h).
The measurement of blood lucigenin-derived chemiluminescence (LDCL) was similar to that described previously (47). Briefly, a 0.2-ml sample was added in a stainless steel cell. The chemiluminescence was measured in a chamber of the Chemiluminescence Analyzing System (Tohoku Electronic Industrial; Sendai, Japan). Photon emission from the sample was counted at 10-s intervals at 37°C and under atmospheric conditions. After 60 s, 0.5 ml of 5 µM lucigenin (bis-N-methy-lacridinium nitrate, Sigma) were injected into the cell. Lucigenin at concentrations of 1–5 µM, sensitive to detect superoxide production by enzymatic and cellular sources, were far below those that stimulated additional superoxide anion production (32). The chemiluminescence in the sample was continuously measured for a total of 300 s. The total amount of chemiluminescence was calculated by integrating the area under the curve and subtracting it from the background level. The assay was performed in duplicate for each timed point and was expressed as chemiluminescence counts per 10 s.
Laboratory measurements. To determine the confounding roles of glucose and insulin in ischemic injury, sinus blood samples, reflecting local concentrations for glucose and insulin concentrations, were assayed.
Exclusion criteria. Animals were omitted from analysis if 1) such severe hypotension was observed that the experiment could not be continued successfully for the duration of the protocol; 2) intractable ventricular fibrillation occurred or antiarrhythmic agents were needed to correct arrhythmia; or 3) heartworms were present in the dogs. Because of influence of collateral circulation on infarct sizes (8), we excluded collateral flow >20% of baseline coronary blood flow to make our study animals homogeneous. Dogs with ventricular fibrillation during reperfusion were resuscitated and converted to a stable rhythm by internal electric shocks (3 x 10 W). The low energy did not result in more cell necrosis (12). Survival percentage was calculated as number of surviving dogs per number of assigned dogs – number of dogs with either collateral >20% or heartworm x 100.
Statistics. The continuous variables are expressed as means ± SD. Differences were tested for hemodynamic variables, infarct size, and AAR among the four groups by non-parametric Kruskal-Wallis statistic analysis followed by a Newman-Keuls post hoc test. Densitometric quantification of signal intensity was performed for Western blot analysis. Background measurements of signal intensity were subtracted individually from each lane. Spearman rank correlation analysis was used to determine the relationship between the parameters and infarct size as a percentage of the AAR. A value of P < 0.05 was considered to be significant.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONDISCLOSURESREFERENCES |
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Dog survival. A total of 73 animals was enrolled in the study. Seven animals in the control group were excluded: 3 because of collaterals, 3 for intractable ventricular fibrillation during coronary occlusion, and 1 for hypotension. Four animals were excluded in the low-dose group: 2 for collaterals and 2 for ventricular fibrillation. Six animals were excluded in the medium- and high-dose groups: 4 for collaterals and 2 for ventricular fibrillation. The remaining dogs were assigned to each group of 14.
Hemodynamics. Preocclusion heart rate, arterial pressure, and left ventricular end-diastolic pressure were similar among the four groups (Table 1). After coronary occlusion, left ventricular end-diastolic pressure markedly increased in controls, whereas heart rate and arterial blood pressure did not change significantly. The pressure rate index, an index of myocardial oxygen demand, was comparable for the four groups before coronary artery ligation and throughout the study.
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Baseline coronary blood flow measured with intracoronary Doppler flow wire was nonsignificantly different among the four groups. Five minutes after occlusion, collateral blood flow in the center of the ischemic region was very low. The decreased amount of coronary blood flow after coronary occlusion was within the same range in the four groups.
Blood glucose and insulin levels. The blood glucose and insulin concentrations in the four groups were measured at baseline, 15 min after troglitazone, 30 min after occlusion, and at 60 and 120 min of reperfusion. At 15 min after medium- and high-dose troglitazone, blood glucose was significantly decreased compared with that at baseline (76 ± 6 vs. 97 ± 4 mg/dl baseline in the medium-dose group; 71 ± 7 vs. 90 ± 7 mg/dl baseline in the high-dose group, both P < 0.05). However, there was no significant change of the blood glucose concentration in the low-dose group after troglitazone was administered compared with baseline. Blood glucose concentrations were corrected and maintained stable in the treated groups by glucose infusion.
Insulin concentrations were significantly decreased 60 and 120 min after reperfusion in dogs administered with troglitazone.
Free radicals. In the control group, LDCL increased significantly at 59 min after myocardial ischemia (Fig. 1). It peaked at 2 min then decreased but remained above the control level 2 h after reperfusion. Dogs in the control group generated a significantly higher concentration of superoxide anion than those in troglitazone-treated animals in response to ischemia-reperfusion. Peak superoxide anion production was 5,728 ± 795 counts/10 s in the control group compared with 3,422 ± 675, 2,543 ± 573, and 2,134 ± 574 counts/10 s in the low-, medium-, and high-dose groups, respectively (all P < 0.05 vs. controls). The medium- and high-dose groups had significantly lower peak concentrations of superoxide anion than the low-dose group, indicating that troglitazone inhibited free radical generation in a dose-response manner.
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Infarct size and AAR. There were no differences in body weight or heart weight among the four groups. There was no significant difference in AAR expressed as a percentage of the left ventricle among the four groups (Fig. 2), indicating that a comparable degree of ischemic risk. After 1 h of coronary artery occlusion followed by 2 h of reperfusion, the necrotic area, expressed as a percentage of the AAR, was 37 ± 8% in the control and 23 ± 10%, 16 ± 7%, and 15 ± 7% in the low-, medium-, and high-dose troglitazone group, respectively (all P < 0.05 vs. controls).
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The correlation coefficient between infarct size and AAR ranged from 0.67 to 0.93 (P < 0.05) in the treated animals (Fig. 3). Troglitazone treatment resulted in a significant downward displacement with all infarct sizes smaller than predicted from the AAR. The medium- and high-dose groups had significantly reduced infarct size compared with the low-dose group, indicating a dose-dependent cardioprotection.
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Histology analysis. Macroscopically, control dogs exhibited confluent infarctions, whereas infarcts in troglitazone-treated groups were patchily distributed, interspersing with islands of viable myocardium. Histological analysis in the control group revealed infarcts composed almost exclusively of contraction band necrosis. The severity of contraction band necrosis was significantly higher in controls compared with the treated groups (2.6 ± 0.5 in controls vs. 2.0 ± 0.7, 1.4 ± 0.9, and 1.4 ± 0.6 in low-, medium-, and high-dose groups, respectivley, all P < 0.05). There was a good correlation between the extent of infarct size normalized by AAR and the severity of contraction band necrosis (r = 0.83, P < 0.0001).
Cx43 Western blot analysis. Figure 4 shows a representative blot and quantitative results from the border zone in which Cx43 band intensities were normalized to the value measured from the sham group. Two predominant forms of Cx43 were detected: one non-phosphorylated form (Cx43-NP; 41 kDa) and the other phosphorylated species (Cx43-P; 43 kDa). Western blot analysis derived from the border zone revealed that the Cx43 band pattern is modified qualitatively in response to ischemia-reperfusion and troglitazone administration. Densitometric analysis of immunoblots revealed a similar total amount of Cx43 signals and a reduced intensity of Cx43-P form in tissues undergoing ischemia-reperfusion. Thus ischemia-reperfusion is associated with progressively reduced phosphorylation of Cx43 from the border zone. The quantitative changes of phosphorylated Cx43 were significantly higher in groups treated with troglitazone (40 ± 15, 36 ± 14, and 32 ± 15% in the low-, medium-, and high-dose groups, respectively) compared with data from the control group (63 ± 17% in the control group, all P < 0.05). Phosphorylated Cx43 expression was similar in response to ischemia-reperfusion in the noninfarcted areas among the groups, consistent with a reversal of dephosphorylation with reperfusion in viable areas (3).
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Quantitative analysis showed a significant relationship between the amount of phosphorylated Cx43 expression assessed by Western blot analysis and contraction band necrosis or infarct size (r = 0.83, P < 0.0001 for contraction band necrosis; and r = 0.73, P < 0.0001 for infarct size, Fig. 5).
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Confocal microscopy (Fig. 6). Western blot data were confirmed by confocal microscopic data analysis. Qualitative immunofluorescent analysis was performed at the border zone. In the sham group, Cx43 antibody produced intense punctate labeling primarily at contacts between cardiomyocytes (Fig. 6A). After ischemia-reperfusion in the control, there was a loss of antibody immunoreactivity (Fig. 6B). These alterations in Cx43 immunostaining were higher in animals treated with troglitazone (low dose in Fig. 6C, medium dose in Fig. 6D, and high dose in Fig. 6E), consistent with the Western blot shown in Fig. 4.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONDISCLOSURESREFERENCES |
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Mechanisms of cardioprotective effects of troglitazone. The mechanisms by which troglitazone administration protected the heart against infarct sizes remain to be defined. However, several factors can be excluded. The first were hemodynamics and collateral circulation. Clearly, troglitazone did not exert any hemodynamic effects or was not associated with an increase in myocardial blood flow at the dose used in this study. Furuse et al. (15) have shown a positive inotropic effect of troglitazone in isolated rat hearts, which was not consistent with our stable hemodynamics throughout the study. This discrepancy may stem from different species (dogs and rats), models (isolated heart vs. in vivo studies), and doses of troglitazone between our results and those of previous reports. The second factors were differences in glucose levels. Previous studies have shown that a change in blood glucose may have been responsible for limiting infarct size (19). During the experiments, blood glucose concentrations were maintained stable by glucose infusion except for the first 15 min after medium-dose and high-dose troglitazone administration. Thus intravenous administration of troglitazone reduced infarct size in anesthetized dogs independent of their alterations in blood glucose concentrations. The final factors were differences in insulin concentrations. Although troglitazone reduces insulin secretion, as shown in this study, the reduced insulin levels cannot be a confounding factor of cardioprotection. Increased insulin levels have been shown to enhance cardioprotection (28), which was not consistent with the troglitazone-induced changes of insulin. Therefore, the possibility was excluded that insulin effects of troglitazone were responsible for the effects on infarct size observed.
Our results show that troglitazone exerts as an in vivo antioxidant in ischemic-reperfused animals of normal glucose levels. The reperfusion state is a condition of excessive oxidative stress, which is thought to increase myocardial infarct size. Troglitazone has been shown to inhibit in vitro production of LDL oxidation at a concentration of 5–10 µM (10). The serum concentration of troglitazone is expected to be about 1 µM at the dose of 1 mg/kg (the low-dose group) because the volume of distribution is 2.5 l/kg (37) and inhibition of LDL oxidation could be partially inhibited at such a concentration. At the dose of 5 mg/kg (the medium-dose group), the serum concentration of troglitazone is expected to be 6 µM at the end of coronary occlusion according to allometric equation (27), indicating that LDL oxidation can be nearly completely inhibited by the antioxidant effects of troglitazone (10). The serum concentrations of troglitazone in the medium- and high-dose groups were above the levels as to be a free radical scavenger during much of reperfusion period. However, there was partial inhibition of free radicals in the low-dose group. Our study confirmed and extended the previous finding of troglitazone with an antioxidant effect with the direct measurement of superoxide anion by LDCL.
Our results here showed qualitative (reduced phosphorylated) changes of Cx43 protein at the border zone during ischemia-reperfusion in groups treated with troglitazone, whereas the total amount of Cx43 did not change. The finding was consistent with a recent work (38) showing that inhibition of gap junction communication resulted in effective reduction of infarct sizes in a rat model of cerebral infarction. The absence of modulation of Cx43 levels at noninfarcted regions by troglitazone administration suggests that this drug did not interact with the basal Cx43 levels. Phosphorylation of Cx43 is an important check point for gap junction function. It has been shown that gap junction uncoupling occurs during acute ischemia due to several factors such as a fall in intracellular pH (pHi), an overload of Ca2+, a loss of ATP, an increase in Na+, and hypoxia (13). However, the rapid restoration of metabolic disorders after reperfusion results in reopening of gap junctions in surviving cells (13). Reopening of gap junctions in the presence of the abnormally high intracellular concentration in neighboring cells and cytoskeletal fragility caused by ischemia induced calcium influx and propagation of contraction band necrosis. Transient gap junction blockade during the first minutes of reperfusion until the cell recovers Ca2+ control has been shown to prevent hypercontracture formation (17). The time sequences of gap junction function can explain, at least in part, reperfusion injury when free radicals massively produce damage. These findings of decreased contraction band necrosis were consistent with our speculation that the major protection of troglitazone is due to inhibition of the development of calcium overload by blocking gap junction functions.
The signaling pathways to mediate free radical-induced Cx43 expression are a complex process. Aikawa et al. (1) have demonstrated that free radicals activate mitogen-activated protein (MAP) kinase pathways in rat cardiomyocytes. Cx43 is a target of the MAP kinase signaling pathway in vivo, and the activation of MAP kinase signaling cascade increased Cx43 phosphorylation (49). Thus troglitazone may induce attenuated expression of Cx43 protein by less activated MAP kinase through decreased formation of free radicals. Second, troglitazone as an antioxidant stimulated the activity of alkaline phosphatase (45), which is the key enzyme to dephosphate Cx43 and in turn altered expression of Cx43 protein. Taken together, troglitazone played an important role in MAP kinase activity and alkaline phosphatase, which in turn altered expression of Cx43 protein possibly by attenuated formation of free radicals.
There were discrepancies between our findings and previous studies. Previous studies have shown that troglitazone has a scavenging effect on reactive oxygen species in mice with alloxan-induced hyperlipoperoxidemia and hyperlipidemia (50) and in humans chronically treated with troglitazone (18). These findings were not consistent with our results, showing that troglitazone did not affect the level of free radicals during the preischemic phase. The reason for the discrepancy is presently unclear. It may reflect the stimulus nature and treatment durations. The stimulus for the generation of free radicals during the preischemic phase is relatively low as shown in Fig. 1, in contrast to in vitro cell culture experiments, in which the stimulus is strong. Besides, free radicals have been identified as a factor that inhibits Cx43 expression in rat hepatocytes (23). Antioxidants prevented the inhibition of gap junction communication between hepatocytes (41). The finding was not consistent with our results, showing that troglitazone as an antioxidant attenuates Cx43 expression in the canine myocardium. The reason for the discrepancy remained unclear. It could be due to different species and different tissue response to antioxidant treatment.
Although the present results suggest that anti-Cx43 effects of troglitazone contribute to the alleviation of contraction band necrosis, we must carefully consider other possible mechanisms for the cardioprotecive effects of troglitazone. Kawasaki et al. (30) have demonstrated that troglitazone directly reduced InsP3-induced Ca2+ release. Propagation of intracellular calcium waves is dependent on diffusion of InsP3 through gap junctions. InsP3 diffuses across cell boundaries, leading to the release of Ca2+ from intracellular stores via InsP3 receptors. The number of cells recruited into the Ca2+ waves would be dependent on the concentration of InsP3 liberated from intracellular stores by the initial stimuli. Thus inhibition of troglitazone-induced InsP3 release can contribute to limited Ca2+ overload during reperfusion. Besides, we cannot exclude the possibility that other mechanisms of troglitazone may be involved via a non-free radical-mediated mechanism such as inhibition of the Na/H exchange (11) and calcium channel blocker (35), increased nitric oxide (24), activated peroxisome proliferator activated receptor- (51), attenuated sympathetic discharge (43), and increased lactate uptake (52), actions that may be protective during myocardial ischemia and reperfusion. Previous studies have demonstrated that troglitazone can act as an inhibitor of Na/H exchange, which provided a cardioprotection by reducing intracellular calcium load (29) and attenuated neutrophil accumulation during ischemia-reperfusion (21). Troglitazone at the concentrations (10 µM) can enhance synthesis of nitric oxide (24) and act as a calcium channel blocker (35) in vitro, which concentrations can be attained used here. Increased nitric oxide has been found to attenuate reperfusion-induced sarcolemmal fragility and reduced formation of contraction band necrosis (36). Recently, Yue et al. (51) have shown that thiazolidinedione as an activator of peroxisome proliferator-activated receptor- can limit infarct size during ischemia-reperfusion by inhibition of the inflammatory response. Also, Saku et al. (43) have demonstrated that troglitazone administration can modulate cardiac sympathetic tone, which leads to decreased influx of calcium and decreases the formation of contraction band necrosis. Finally, troglitazone administration has been shown to provide cardioprotection by increasing lactate uptake after reperfusion in a study performed in troglitazone-treated pigs for 8 wk (52). Bahr et al. (2) have shown a different response between acute and chronic administration of troglitazone in rat cardiomyocytes. Thus whether these metabolic effects were responsible for the attenuated infarct sizes in a model of acute administration of troglitazone remained unclear.
Study limitations. Although we have demonstrated qualitative changes of Cx43 protein expression in response to troglitazone administration, they do not necessarily correlate with functional changes. We did not show reduced intracellular calcium overload either by buffering the cytosolic Ca2+ concentration via patch clamp or by directly measuring the cytosolic Ca2+ concentration by means of fluorescent emission. However, the techniques are impossible to perform in an in vivo study. The severity of contraction band necrosis, an indirect method to assess the calcium overload, was evaluated by histological analysis, which showed a close relation between the amount of Cx43 expression and the severity of contraction band necrosis.
It is concluded that troglitazone, at therapeutic concentrations, limits infarct size by decreasing reperfusion-induced free radicals. The beneficial effects of troglitazone appear to be mediated, at least in part, through the reduced phosphorylation of gap junctional protein. This provides a perspective for the analysis of the pathophysiology and treatment of acute myocardial infarction.
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DISCLOSURES |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONDISCLOSURESREFERENCES |
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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Y. Xu, M. Gen, L. Lu, J. Fox, S. O. Weiss, R. D. Brown, D. Perlov, H. Ahmad, P. Zhu, C. Greyson, et al. PPAR-{gamma} activation fails to provide myocardial protection in ischemia and reperfusion in pigs Am J Physiol Heart Circ Physiol, March 1, 2005; 288(3): H1314 - H1323. [Abstract] [Full Text] [PDF]
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P < 0.05 vs. control at the same sampling point; 
P < 0.05 vs. low-dose group at the same sampling point.
