EFFECT OF ANGIOTENSIN II ON ALDOSTERONE SECRETION IN THE CONSCIOUS RAT

Abstract

SUMMARY Aldosterone secretion has been shown to increase in response to exogenous angiotensin II in man and many experimental animals. However, the rat adrenal has traditionally shown little or no response to angiotensin in experimental protocols using either angiotensin added to incubating adrenal tissue or angiotensin infused into anaesthetized rats. In this study, changes in plasma aldosterone concentration in response to a 20 min infusion of small amounts of angiotensin II into conscious rats were compared with the changes produced in sodium pentobarbitone anaesthetized rats. Both groups showed typical arterial pressure increases in response to infusion: 5 ng angiotensin/kg/min producing approximately a 12 mmHg pressure increase and 20 ng angiotensin/kg/min producing approximately a 25 mmHg increase. Plasma aldosterone concentration increased in anaesthetized rats only at the higher infusion rate, reaching a value 37 ± 6v. 17 ± 2 (s.e.m.) ng/100 ml (n = 5) in anaesthetized control animals. In contrast, plasma aldosterone concentration in conscious rats increased to 69 ± 24 and 106 ± 43 ng/100 ml at the two infusion rates, respectively, v. 13 ± 5ng/100ml in conscious controls. This marked sensitivity indicates that the acute response of the rat to angiotensin infusion is similar to that of other experimental animals and man; however, the response is severely attenuated by anaesthesia and surgical preparation.