Vasodilating beta-adrenoceptor blocking drugs do not redistribute myocardial flow during acute coronary ligation in dogs

Comparative effects of arotinolol, labetalol and propranolol on regional myocardial dysfunction induced by flow-limiting coronary stenosis in anesthetized dogs

Effects of arotinolol, a combined alpha- and beta-adrenoceptor blocking agent, on regional myocardial dysfunction produced by severe coronary stenosis in anesthetized dogs were examined and compared with those of labetalol and propranolol. Doses of these three antagonists were selected to produce a comparable degree of the negative chrono- and inotropic effect but a different potency of alpha-adrenoceptor blockade (labetalol greater than arotinolol). Regional myocardial function measured as segment shortening (%SS) was decreased to around 2-3% by constriction of the left circumflex coronary artery (LCX), and then drug or saline was administered i.v. The stenosis of LCX was released 30 min after the administration. No significant alteration in hemodynamic and contractility parameters was seen as compared to the predrug value up to at least 30 min after saline i.v. Arotinolol and propranolol both reduced heart rate and peak positive left ventricular dP/dt (LVdP/dt) without a significant change in LCX flow. Concomitantly, %SS distal to a coronary stenosis was significantly improved by arotinolol and propranolol. On the other hand, labetalol significantly reduced LCX flow probably due to systemic hypotension and failed to improve %SS in the ischemic area, although the agent markedly decreased heart rate and LVdP/dt. These results indicate that arotinolol improves impaired regional myocardial function distal to a coronary stenosis in a similar manner with propranolol.

Effects of four angiotensin I converting enzyme inhibitors on regional myocardial blood flow and ischemic injury during coronary artery occlusion in dogs

The effects of 4 angiotensin I converting enzyme inhibitors (ACEI), captopril, enalapril, ramipril, and trandolapril, were investigated on regional myocardial blood flow (RMBF, radioactive microspheres) distribution in ischemic and nonischemic zones and on ST-segment elevation in ischemic zones during intermittent coronary artery occlusion in anesthetized dogs. The 4 ACEI inhibited plasma ACE activity to an almost similar extent. All similarly reduced systemic blood pressure, an effect related to a decrease in systemic vascular resistance. Heart rate and myocardial contractility were not affected, but myocardial oxygen consumption presumably decreased because of the reduction in afterload. RMBF and their distribution (between epicardial and endocardial layers and between nonischemic and ischemic zones) were not modified by ACEI. Coronary vascular resistance was slightly decreased in nonischemic zones. ACEI had no effect on ST-segment elevation in ischemic zones. Thus, in this experimental model, all ACEI exhibited the same profile, including no change in RMBF and affording no protection against ischemic injury.