ROLE OF ANGIOTENSIN III IN THE REGULATION OF BLOOD PRESSURE, PLASMA ALDOSTERONE AND PLASMA RENIN ACTIVITY IN RABBIT

ABSTRACT To evaluate the role of angiotensin III in the control of blood pressure, plasma aldosterone and plasma renin activity (PRA), the pressor, steroidogenic and PRA-suppressing effect of angiotensin III was studied in rabbits with or without simultaneous constant infusion of Ile 7 -angiotensin III, an analogue of angiotensin III, or Sar 1 Ala 8 -angiotensin II, an analogue of angiotensin II, and compared with the effect of angiotensin II. Infusion of 30 ng/kg/min of angiotensin III or angiotensin II produced a twofold increase in plasma aldosterone. Pressor response to angiotensin III was approximately one tenth of that of angiotensin II. Infusion of angiotensin II suppressed the PRA significantly, while infusion of angiotensin III did not suppress it. Angiotensin II or angiotensin III induced-increase in plasma aldosterone was attenuated by the pretreatment with either Ile 7 -angiotensin III or Sar 1 Ala 8 -angiotensin II. Pressor or PRA-suppressing action of angiotensin II was unaffected by the pre-treatment with Ile 7 -angiotensin III, while it was significantly inhibited by pre-treatment with Sar 1 Ala 8 -angiotensin II. This study indicates that angiotensin III or angiotensin III analogues affect the adrenal glands selectively and suggests that there are differences between the receptor sites for angiotensins in vascular smooth muscle, kidney and those in the adrenal cortex.