Regional Haemodynamic Effects of Angiotensin II (3-8) in Conscious Rats

1. It has been reported that angiotensin II (AII) (3-8) causes endothelium-dependent renal cortical vasodilatation, in anaesthetized rats, through interaction with a novel receptor that shows no affinity for the AT1-receptor antagonist, losartan. Therefore in order to get a fuller profile of the regional haemodynamic effects of AII (3-8) in conscious rats we assessed its renal, mesenteric and hindquarters vascular effects, and compared them to the responses elicited by AII and AIII. 2. AII and AIII (1.25, 12.5 and 125 pmol kg-1) caused dose-dependent pressor and renal and mesenteric vasoconstrictor effects. At doses up to 125 pmol kg-1, AII (3-8) was without any cardiovascular effects, but with doses of 1.25 and 12.5 nmol kg-1 there were dose-dependent increases in mean arterial blood pressure and reductions in renal and mesenteric flows and vascular conductances. The responses to AII (3-8) (12.5 nmol kg-1) were abolished by losartan (20 mumol kg-1). 3. Since it has been found that pretreatment with L-arginine can reveal a vasodilator effect of AII (3-8) on rabbit pial arterioles, we assessed responses to AII (3-8) (12.5 nmol kg-1) before and 5 min after onset of a primed infusion of L-arginine (1.4 mmol kg-1 bolus, 1.4 mmol kg-1 h-1 infusion). Responses to AII (3-8) were unchanged by L-arginine. 4. The results are consistent with AII (3-8) being a less effective agonist than All (or AIII) at the AT1-receptor, but provide no evidence for AII (3-8) interacting with a novel receptor that shows no affinity for losartan.