Mechanism of pressor effects of angiotensin II microinjected into the fourth ventricle of rabbits

Abstract

The experiments were performed on 53 anesthetized, paralyzed and ventilated rabbits. 1) Microinjectjon of 5 μg angiotensin II (A II) into the fourth ventricle elicited increase of mean arterial pressure and renal nerve discharges, but decrease of heart rate. When the baroreceptor reflex was eliminated before microinjection, the decrease of heart rate no longer occurred. 2) Pretreatment with 1 μg prazosin decreased the pressor effect of A II and eliminated the increase of renal nerve discharges, whereas 3 μg yohimbine produced no effect on the pressor response of A II. 3) Pretreatment with 1 μg prazosin and 10 μ1 arginine-vasopressin antiserum together could abolish the pressor effect of A II. The experimental results suggest that microinjection of A II into the fourth ventricle had central pressor effect, which might be mediated through central α₁-adrenoceptor and central vasopressin.

Keywords

angiotensin II / vasopressin / prazosin / mean arterial pressure / fourth ventricle

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