Adrenergic control of renin in euhydrated and water-deprived conscious dogs

These experiments evaluated the relative contributions of alpha- and beta-adrenoceptors to control of plasma renin activity (PRA) in conscious dogs in which PRA was elevated to two- and threefold basal levels by the orthostatic stress of passive quadruped standing and by 24-h water deprivation. All dogs were uninephrectomized and surgically prepared with chronically indwelling catheters in the aorta, vena cava, and remaining renal artery at least 10 days before experiments. Simultaneous direct renal arterial (ia) infusion of phenoxybenzamine and propranolol decreased PRA by 50% in euhydrated standing dogs and by 70% in dehydrated standing dogs without changing mean arterial pressure or heart rate. In euhydrated dogs, both ia phenoxybenzamine alone and ia propranolol alone significantly decreased PRA, but the effect of propranolol was greater than that of phenoxybenzamine. In dehydrated dogs, ia infusion of phenoxybenzamine alone did not significantly decrease PRA, whereas propranolol alone decreased PRA to nearly the same extent as combined ia alpha- and beta-adrenoceptor blockade. The majority of the adrenergically mediated component of PRA observed during orthostatic stress and dehydration in conscious dogs is therefore mediated by beta-adrenoceptors. However, PRA was similarly reduced whether propranolol was infused ia or intravenously. Thus the site of action of propranolol (intrarenal vs. extrarenal) could not be identified by these experiments.