Effect of angiotensin inhibition on the coronary artery lower pressure limit in anesthetized dogs

The renin-angiotensin system plays a critical role in regulating vasoconstr iction and vasodilatation that can influence myocardial blood flow and its transmural distribution. We tested the hypothesis that angiotensin inhibiti on can induce a leftward shift of the coronary autoregulatory pressure-flow relation and preserve distribution of myocardial blood flow at lower coron ary perfusion pressures. We established circumflex artery pressure-flow rel ations under baseline conditions and after intracoronary enalaprilat or los artan potassium. Thereafter, transmural myocardial blood flow was measured at baseline and at the lower coronary pressure limit (LPL). With enalaprila t, the LPL was shifted leftward from 48 +/- 6 mmHg at baseline to 43 +/- 3 mmHg (P = 0.026); with losartan, the LPL was shifted leftward from 48 +/- 1 0 mmHg at baseline to 41 +/- 5 mmHg (P = 0.027). The leftward shift occurre d while cardiac hemodynamics and Mv-dotO(2) were maintained at control leve ls. These results indicate that angiotensin inhibition extends the range of coronary autoregulation to lower LPL while preserving myocardial blood flo w distribution, a physiologic effect that might explain the lower incidence of coronary events in treated patients.