Comparison of Prizidilol, a New Antihypertensive Drug with Combined Arteriolar Vasodilator and β-Adrenoceptor Blocking Actions, with Hydralazine and Propranolol in Conscious Dogs with Chronic Atrioventricular Block

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Abstract
The effects of prizidilol, a novel antihypertensive agent with vasodilator and beta-adrenoceptor blocking actions, were compared with those of hydralazine and propranolol in conscious dogs with chronic atrioventricular block. Prizidilol significantly increased atrial rate, mainly through reflex reduction of atrial vagal tone in response to its hypotensive effect. Hydralazine also significantly raised atrial rate, while propranolol did not affect it. Prior administration of pindolol, which raised atrial rate to a degree comparable to that achieved with prizidilol and hydralazine, entirely suppressed the atrial tachycardiac effects of both drugs. Prizidilol did not affect ventricular rate on average, whereas hydralazine raised it and propranolol lowered it, both significantly. In some dogs, prizidilol raised ventricular rate like hydralazine; in others, it lowered it like propranolol. In both cases, variation was related to basal ventricular rate. The pattern of these effects was the same as that observed with pindolol. Prior treatment with pindolol almost suppressed the ventricular chronotropic effects of prizidilol, apparently through beta-adrenoceptor blockade.

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