The role of the renin-angiotensin system in mediation of adrenal catecholamine secretion in the cat induced by intrarenal β-adrenergic stimulation

Isoproterenol infusion (0.1 μg/kg per min) into the renal artery of the cat induced an increase in plasma renin concentration (PRC) from 14.3±5.7 (mean±SE) ng angiotensin I/ml per hr to 56.8±7.7 after 70 minutes (P<0.05) and an increase in catecholamine secretion rate from 38.7±6.0 ng/kg per 10 min to 180.0±40.0 after 70 minutes (P<0.001). Intravenous infusion of the same dose of isoproterenol had no significant effect on adrenomedullary catecholamine secretion rate. Isoproterenol induced preferential norepinephrine release: the ratio of norepinephrine to epinephrine secretion changed from 11.5:23.7 during the control period to 130.0:40.1 70 minutes after the start of isoproterenol administration. Intrarenal infusion of propranolol (3.0 mg/kg per min) inhibited renal renin release and adrenal catecholamine secretion in response to intrarenal isoproterenol. Intravenous infusion (0.4 μg/kg per min) of an angiotensin II antagonist [Sar¹, Ileu⁸]angiotensin II abolished the catecholamine response to intrarenal isoproterenol infusion. It is suggested that intrarenal isoproterenol infusion stimulates renal renin response and angiotensin production which, in turn, stimulates a preferential secretion of adrenomedullary norepinephrine.