Pharmacological Interference with the Cardiac Renin-Angiotensin System

Biochemical, pharmacological, and molecular biological data provide evidence for the presence of a cardiac renin-angiotensin system. Tissue angiotensins were demonstrated in all regions of the mammalian heart. Reduction of cardiac angiotensin II formation after oral administration of converting enzyme (CE) inhibitors in nephrectomized animals points to local generation of these peptides. Functional studies in isolated working rat hearts subjected to transient regional ischemia and reperfusion showed that there is aggravation of arrhythmias as well as exhaustion of energy status by angiotensins. This was prevented by CE inhibition and/or perfusion with bradykinin (BK.). which in turn could be competitively antagonized with a BK antagonist. Intracoronary infusion of low-dose bradykinin attenuated ischemia-reperfusion injuries and reduced enzyme and lactate release in anesthetized dogs. Oral pretreatment with the CE inhibitor ramipril in rats, in doses that did not affect the elevation of blood pressure caused by aortic constriction, could prevent induction of as well as cause regression of established cardiac hypertrophy. In contrast, pure vasodilation was without effect on cardiac enlargement despite lowering blood pressure, pointing to a possible trophic influence of angiotensin II. Thus, apart from afterload reduction and euvolumia produced by CE inhibition, the outstanding efficacy of this therapeutic approach in congestive heart failure and cardiac hypertrophy and its potential usefulness in myocardial ischemia may also be explained by intracardiac suppression of angiotensin II generation and bradykinin degradation.