Role of central effects of angiotensin in response to haemorrhage in the dog

Renal modulation of electrically stimulated adrenal medullary secretion

In acutely anephric dogs, depressed reflex adrenal medullary secretion (AMS) may be related to low plasma angiotensin. Either local (adrenal medulla) or central nervous system mechanisms are responsible. Local influences of acute bilateral nephrectomy on AMS were evaluated after left splanchnic nerve section. Two groups of five healthy, fasted mongrel dogs (16-20 kg) were prepared (Na pentobarbital iv anesthesia, 98% O2/2% CO2, Harvard volume ventilator) at celiotomy with blood pressure and sampling catheters per femoral arteriotomies and left adrenal-femoral venous T-shaped Silastic shunt. Group 2 dogs had acute bilateral nephrectomy. The acutely divided distal left splanchnic nerve was arranged for electrical stimulation (Grass, bipolar nerve stimulator, 1 0 V, 1-msec delay, 10 Hz, 10-msec square wave). Heparin anticoagulation was maintained and arterial pH monitored. Simultaneous adrenal vein, aortic blood sampling, and adrenal blood flow (F) determinations followed 10-min periods of alternating electrical stimulation and nerve rest. AMS for epinephrine (E) and norepinephrine (NE) was calculated [E and NE plasma concentration (single isotope radioenzymatic technique) differences of adrenal vein minus aorta multiplied by F]. Results were grouped, analyzed for variance, and compared (Wilcoxon unpaired rank sum, Student's test, Fischer's tables, ANOVA). Low aortic E, NE concentrations confirmed absent systemic adrenergic stimulation. The AMS ratio of NE:E was low in the anephric group. At the first stimulation interval NE:E was 0.28 +/- 0.14 (1 SD) in renal intact dogs vs 0.11 +/- 0.04 in anephric dogs, P less than 0.05. At rest NE:E was 0.33 +/- 0.12 in group 1 vs 0.17 +/- 0.02 in group 2 dogs, P less than 0.02. Plasma NE was also low in the anephric group (289 mg/liter +/- 126 (1 SD) vs 612 +/- 189, P = 0.033, resting).(ABSTRACT TRUNCATED AT 250 WORDS)

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

Isoproterenol infusion (0.1 microgram/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 microgram/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 release and angiotensin production which, in turn, stimulates a preferential secretion of adrenomedullary norepinephrine.

Renin-angiotensin mediation of adrenal catecholamine secretion induced by haemorrhage

The mechanism involved in catecholamine (CA) release from cat adrenal gland, in response to haemorrhage was studied. In intact cats, in cats with bilateral cervical vagotomy or following bilateral ureteral ligation, haemorrhage induced an increased catecholamine release from the adrenal (with increased percentage of noradrenaline). Acute bilateral nephrectomy, chronic sodium loading with repeated administration of desoxycorticosterone acetate (DOCA), or acute denervation of the adrenal gland, completely abolished the increased CA release from the adrenal gland following haemorrhage. Haemorrhage induced an increase of plasma renin concentration in intact cats and after ureteral ligation but there was no increase in plasma renin after haemorrhage in cats with bilateral nephrectomy or following pretreatment with DOCA and salt load. Following haemorrhage in intact cats, blood pressure showed an immediate fall followed by rapid recovery. The recovery of blood pressure after haemorrhage was abolished in cats with bilateral nephrectomy. It is concluded that the adreno-medullary response to haemorrhage in the cat, depends primarily on the intact renal renin angiotensin system. Angiotensin, generated peripherally, probably affects the CNS and activates the sympathetic nerves.