THE RATIO OF CARDIAC TO VASCULAR β-RECEPTOR BLOCKADE OF ATENOLOL AND PROPRANOLOL IN SPONTANEOUSLY HYPERTENSIVE RATS IN VIVO

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Ratios of cardiac to vascular β-receptor blockade (C : V ratios) of atenolol and propranolol were determined in pentobarbital anesthetized spontaneously hypertensive (SHR) rats. These values and the cardiovascular responses to isoproterenol were compared with those of age-matched normotensive control (Donryu, DON) rats reported previously. Mean blood pressure (BP) and heart rate (HR) were recorded. Full dose-response curves for isoproterenol were constructed in BP and HR. In vivo pD₂ values of isoproterenol (potencies), were not different between DON and SHR rats, although the maximal responses to isoproterenol (efficacy) were significantly suppressed in SHR rats. C : V ratios of atenolol and propranolol in SHR rats were 7.95 and 0.44, respectively. As the values in DON rats were 9.77 and 1.20, respectively, C : V ratios of atenolol and propranolol were decreased in SHR rats. Markedly decreased C : V ratios of propranolol in SHR rats may explain its relatively weak antihypertensive action.