chymostatin and Myocardial-Infarction

The aim was to investigate the role of local formation of angiotensin II and bradykinin in the reduction of myocardial infarct size.. Bilaterally nephrectomised male mongrel dogs were used. Effects were compared of pretreatment with three inhibitors of angiotensin II forming enzyme-captopril (an angiotensin converting enzyme inhibitor), nafamostat (a serine protease inhibitor), and chymostatin (a cysteine protease inhibitor)--on left anterior descending coronary artery occlusion. Haemodynamic variables were monitored and blood was collected from the anterior interventricular vein and the aorta. Angiotensin I, angiotensin II, and bradykinin were measured by radioimmunoassay. After 90 min of occlusion, infarct sizes were determined by a macroscopic enzyme technique.. Angiotensin II release into the anterior interventricular vein increased from 0.03(SEM 1.19) pg.min-1 (before coronary occlusion) to 4.64(1.37) pg.min-1 (n = 14, p < 0.05), while angiotensin I release and plasma renin activity remained unchanged. The increase in angiotensin II release was inhibited by nafamostat and chymostatin, but not by captopril. Bradykinin release increased from -3.18(2.72) (before coronary occlusion) to 34.7(12.3) pg.min-1 (n = 14 p < 0.05) by 30 min after occlusion. This increase was augmented by captopril, from 4.10(2.86) before occlusion to 97.8(39.6) pg.min-1 at 5 min after occlusion (n = 12, p < 0.05), but not by nafamostat or chymostatin. Infarct size was smaller (p < 0.05) in the captopril group than in the control group.. Angiotensin II is locally produced in the ischaemic heart by both serine protease(s) and chymostatin inhibitable protease(s), but not by angiotensin converting enzyme. From the reduction in myocardial infarct size produced by angiotensin converting enzyme inhibition, it seems that bradykinin accumulation may play a more important role than the suppression of angiotensin II formation.

Topics: Angiotensin II; Animals; Benzamidines; Bradykinin; Captopril; Dogs; Guanidines; Hemodynamics; Male; Myocardial Infarction; Oligopeptides; Serine Proteinase Inhibitors

To test the hypothesis that cellular proteinases contribute to ischemic myocellular death, measurements were made of tyrosine release (an index of overall proteolysis) from incubated slices of nonischemic and ischemic myocardium obtained at various times after coronary artery occlusion in rats. Proteolysis failed to increase in ischemic myocardium throughout the first 24 hours of occlusion, when irreversible damage develops, indicating that cellular proteinases do not undergo generalized activation in this phase. These data represent the first assessment of myocardial proteolysis throughout the development of ischemic death, and suggest that cellular proteinases do not play a causal role in this process. However, the possibility remains that ischemia selectively accelerates the breakdown of vital proteins, a phenomenon that may not be detected by measuring overall proteolysis. To determine whether future studies on the effects of proteolytic inhibition on infarct size are feasible, the ability of the proteinase inhibitors antipain, leupeptin, pepstatin and chymostatin, given in vivo, to interfere with proteolysis in ischemic myocardium was also evaluated. Leupeptin (10 or 40 mg/kg) inhibited proteolysis in a dose-related fashion (-49 and -72%, respectively, p less than 0.001). Antipain (20 mg/kg) decreased protein breakdown by 60% (p less than 0.001). The combination of antipain (20 mg/kg), leupeptin (40 mg/kg) and pepstatin (5 mg/kg) suppressed proteolysis almost completely at both 15 minutes (-88%, p less than 0.001) and at 6 hours (-72%, p less than 0.05) of ischemia, that is, throughout the development of irreversible injury. These results demonstrate that whatever proteolysis is occurring during acute myocardial infarction is largely mediated by cathepsins A, B, D, L and H and by calcium-activated neutral protease (that is, the enzymes sensitive to the inhibitors used). Because antipain, leupeptin and pepstatin significantly suppress such proteolysis, these agents might be useful in further assessing any potential contribution of cellular proteinases to the production of ischemic myocellular death. In addition, this study provides a new experimental model that affords serial assessments of regional myocardial proteolysis during the evolution of myocardial infarction.

Topics: Animals; Antipain; Cathepsins; Cell Survival; Chymotrypsin; Endopeptidases; Heart; Leupeptins; Male; Myocardial Infarction; Myocardium; Oligopeptides; Pepstatins; Protease Inhibitors; Rats; Rats, Inbred Strains; Time Factors; Tyrosine