Beta-adrenoreceptor blockade in the conscious rabbit: effects on plasma renin activity and blood pressure.

The administration of a single dose of dl-propranolol, 1 mg/kg i.v., in the conscious unstimulated rabbit produced effective beta-adrenoreceptor blockade (inhibition of isoprenaline tachycardia) for 150 min. During this period there was a positive correlation between plasma concentrations of propranolol and the degree of beta-blockade observed. In a further group of animals treated with propranolol, plasma renin activity (PRA) fell to 50% of control (P < 0.001) within 60 min, the rate of change of PRA also correlating with plasma propranolol levels. Similarly, there were reductions in mean blood pressure (P < 0.025) and heart rate (P < 0.025). Statistical relationships between the fall in blood pressure and either pre-treatment PRA or the change in PRA were consistent with the hypothesis that the hypotensive effect of propranolol was dependent upon its suppression of renin release. However, an alternative possibility that the fall in blood pressure was due to an acute reduction in cardiac output could not be excluded.