INTRACEREBROVENTRICULAR ADMINISTRATION OF ANGIOTENSIN-II INCREASES HEART-RATE IN THE CONSCIOUS TROUT

The central effect of angiotensin II on cardiovascular activity has be en investigated in conscious trout bearing an intracerebroventricular (i.c.v.) cannula and an intra-arterial catheter. I.c.v. injection of t he angiotensin II agonist [Asn(1),Val(5)]AII (6.2-50 pmol) induced a d ose-dependent increase in heart rate and arterial blood pressure. Cent ral administration of the angiotensin II antagonist DuP 753 (5 nmol) 3 0 min before i.c.v. injection of [Asn(1),Val(5)]AII totally prevented the tachycardia and reduced the hypertension induced by the angiotensi n II agonist. Intra-arterial injection of arginine-vasotocin (12.5 pmo l) caused a bradycardia associated with a marked increase in arterial blood pressure. I.c.v. injection of [Asn(1),Val(5)]AII totally blocked the bradycardia induced by arginine-vasotocin and this effect was pre vented by central administration of DuP 753. In contrast, [Asn(1),Val( 5)]AII did not affect the increase in blood pressure induced by argini ne vasotocin. Suppression of the vagal tone by atropine treatment tota lly blocked the central effect of [Asn(1),Val(5)]AII. These results sh ow that angiotensin II acts directly on the trout brain to increase bl ood pressure and heart rate. The effect of angiotensin II is mediated through a receptor related to the mammalian-AT1 receptor type.