Effects of ACE Inhibitors on Circulating Versus Cardiac Angiotensin II in Volume OverloadInduced Cardiac Hypertrophy in Rats

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Abstract
Background Cardiac volume overload by an aortocaval shunt increases left ventricular end-diastolic pressure (LVEDP) and plasma and cardiac renin activity and results in LV hypertrophy. To a similar extent, the angiotensin-converting enzyme (ACE) inhibitors enalapril and quinapril prevent the increase in LVEDP. However, only quinapril attenuates the development of LV hypertrophy. We hypothesize that a low affinity of enalapril for cardiac ACE results in continuing generation of cardiac angiotensin II and thus hypertrophic growth of cardiomyocytes. Methods and Results In the present study, we assessed plasma and cardiac angiotensins I and II 1 and 7 days after aortocaval shunt and the effects of enalapril and quinapril started 3 days before surgery on plasma and cardiac angiotensin I and II at the same time points. Aortocaval shunt increased plasma angiotensin II at 1 day by 180%, but only a small increase (by 40%) persisted at 7 days. Aortocaval shunt increased LV angiotensin II by 100% and 65% at 1 and 7 days, respectively. Both blockers similarly prevented the increase in plasma angiotensin II by aortocaval shunt at both time points. In contrast, only quinapril prevented the rise in LV angiotensin II induced by shunt at 1 and 7 days. Conclusions Aortocaval shunt increases LVEDP and plasma and cardiac angiotensin II and results in LV hypertrophy. Only prevention of the increase in LVEDP and in plasma and cardiac angiotensin II attenuates the development of LV hypertrophy, consistent with the concept that angiotensin II is involved in the development of cardiac hypertrophy by aortocaval shunt by both hemodynamic and cardiac trophic effects. This study is the first to show that differences in affinity for cardiac ACE may determine the effect of ACE inhibitors on cardiac angiotensin II and therefore cardiac hypertrophy.