Facilitatory Role of the Renin-Angiotensin System in Controlling Adrenal Catecholamine Release in Hemorrhaged Dogs

Abstract

Effects of the renin-angiotension system (RAS) on adrenal catecholamine release in response to hemorrhagic hypotension and splanchnic nerve stimulation (SNS) were studied in pentobarbital-anesthetized dogs. In hemorrhage experiments, mean blood pressure (MBP) was maintained at 50 mm Hg for 60 min by bleeding the arterial blood into a pressurized bottle. In the renal intact group (control), epinephrine (EPI) and norepinephrine (NE) output from the adrenal gland increased markedly during hemorrhagic hypotension: from 45 +/- 13 and 4.7 +/- 0.9 to 1,167 +/- 202 and 169 +/- 30 ng/min at 60 min after onset of hemorrhage, respectively. The increases in catecholamine output during hemorrhagic hypotension in the renal-intact group pretreated with captopril (1 mg/kg intravenously, i.v.) and in the renal-ligated group were significantly smaller than those in the control group. The increases in catecholamine output in the renal-ligated group infused with angiotensin II (AngII 10 ng/kg/min i.v.) were comparable to those in the control group. In SNS experiments, AngII infusion (10 ng/kg/min i.v.) enhanced increases in catecholamine output induced by 3 Hz SNS significantly. Captopril (1 mg/kg i.v.) did not affect the SNS-induced increases in catecholamine output. These results suggest that the renal RAS facilitates reflex release of adrenal catecholamines during hemorrhagic hypotension, at least in part, by acting directly on the release process of catecholamines from dog adrenal gland.