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.