Dilation of Epicardial Arteries in Conscious Dogs Induced by Angiotensin-Converting Enzyme Inhibition with Enalaprilat

Abstract
Summary Vasodilators may provoke myocardial ischemia in patients with coronary heart disease. Therefore, we analyzed in conscious dogs the effect of angiotensin-converting enzyme (ACE) inhibition by enalaprilat on parameters potentially important to provocation of myocardial ischemia, such as sympathetic activity, myocardial oxygen consumption, and vascular tone in coronary conduit and resistance vessels. Under normal sodium intake (2–4 mEq/kg/day), enalaprilat (0.03 and 0.3 mg/kg i.v. during 5-min infusion with 30-min intervals, n = 8) did not modify the norepinephrine release rate into plasma (a parameter of overall sympathetic activity). The higher dosage reduced myocardial oxygen consumption (to 87 ± 2% of control), mean arterial pressure (MAP) (to 90 ± 1) and coronary conduit artery tone (normalized Δ diameter: +3.2 ± 0.7%) without dilating coronary resistance vessels. Following rennin–angiotensin activation by sodium deprivation (3 × 1 mg/kg furosemide plus 7 days sodium intake <0.2 mEq/day), enalaprilat similarly lowered myocardial oxygen consumption and reduced vascular tone both in coronary conduit (normalized Δ diameter: +4.0 ± 0.9%) and resistance vessels (Δ coronary flow: +45 ± 12%). Although MAP declined to 76 ± 6%, heart rate and norepinephrine release rate were not modified significantly. We propose that the dilation of epicardial arteries results from a direct intramural action. Enalaprilat seems unlikely to provoke myocardial ischemia even in states with a strongly activated renin–angiotensin system.