Central site for pressor action of blood-borne angiotensin in rat

A previous study demonstrated that the threshold dose of intra-arterial angiotensin II required to induce a pressor response in the rat was significantly lower when the drug was administered into the carotid artery than when administered into the abdominal aorta. This result was interpreted to indicate that part of the increase in arterial pressure produced by low concentrations of blood-borne angiotensin in this species was the result of an effect on structures in the central nervous system selectively accessible via the carotid vascular bed. The purpose of the present study was to establish more precisely the site of the pressor action of angiotensin within the central nervous system. The central component of the pressor effect of angiotensin was quantified as the difference in pressor responses to intracarotid and intra-aortic infusions of angiotensin II (delta c-a). In conscious rats, delta c-a was attenuated by administration of the angiotensin antagonist, saralasin, into the third cerebral ventricle. In rats with chronic electrolytic lesions of the anteroventral third ventricle (AV3V), delta c-a was abolished. Periventricular structures surrounding the third ventricle appear to mediate the central component of the pressor action of blood-borne angiotensin in the rat.