Sulfinalol

Combinations of beta-adrenoceptor blockers and vasodilators have proved highly useful in antihypertensive therapy. Studies of the mechanisms of action of several agents that combine these effects within a single molecule are described in this report. Labetalol, SCH 19927, sulfinalol, MK-761, pindolol, and prizidilol, in contrast to propranolol, decreased blood pressure of spontaneously hypertensive rats (SHR). All except labetalol and SCH 19927 increased heart rate. In anesthetized dogs, all of these agents (except propranolol) produced vasodilatation on intra-arterial administration into the femoral vascular bed and, given i.v., lowered blood pressure after ganglionic blockade. In contrast to the other agents, labetalol and SCH 19927 caused only minimal increases in heart rate in ganglionically blocked dogs. The vasodilator and hypotensive actions as well as the antihypertensive effect in SHR of labetalol, SCH 19927, sulfinalol, and pindolol were inhibited by propranolol pretreatment but those of prizidilol were not, suggesting that the hypotensive and vascular effects of labetalol, SCH 19927, sulfinalol, pindolol, and MK-761 are mediated by activation of vascular beta-receptors. However, labetalol and SCH 19927 in particular differ from agents of this class as well as other beta blockers with strong intrinsic sympathomimetic actions in that their agonist activity is primarily directed at blood vessels and not the heart.

Several new beta-adrenoceptor antagonists (sulfinalol, MK 761, and prizidilol) have been reported to possess direct vasodilator activity in addition to blocking beta-receptors. The mechanism of the hypotensive and vasodilator actions of these agents was examined and compared to that of pindolol and hydralazine. Intraarterial injection of each agent increased blood flow in the sympathetically denervated hindlimb of anesthetized dogs. Doses increasing flow by 50 ml/min (ED50) were 0.48, 0.24, 331, 0.3, and 51 micrograms for sulfinalol, MK 761, prizidilol, pindolol, and hydralazine, respectively, Intravenous injection of each agent reduced blood pressure of anesthetized, ganglion-blocked dogs. Vasodilation and hypotension to sulfinalol, MK 761, and pindolol, but not prizidilol or hydralazine were attenuated by propranolol pretreatment. Oral administration of sulfinalol (2.5 mg/kg), MK 761 (2.5 mg/kg), prizidilol (10 mg/kg), pindolol (0.1 mg/kg), and hydralazine (2.5 mg/kg) reduced pressure of conscious spontaneously hypertensive rats. Antihypertensive actions of sulfinalol and pindolol, but not MK 761, prizidilol, and hydralazine were inhibited by propranolol pretreatment (25 mg/kg, p.o.). With the exception of hydralazine, each agent demonstrated effective beta-adrenergic blockade at the antihypertensive dose tested as judged by inhibition of the chronotropic responses to sympathetic stimulation and isoproterenol in pithed rats. These data suggest that the acute vasodilator and blood pressure lowering effects of sulfinalol, MK 761, and pindolol, but not prizidilol and hydralazine, are mediated, at least in part, through activation of vascular beta-receptors.