Effects of Carotid Occlusion and Angiotensin II on Vasopressin Secretion in Intact and Vagotomized Conscious Rabbits*

Abstract

Experiments were performed in conscious rabbits with sectioned aortic depressor nerves to determine whether there is an interaction between angiotensin II (Ang II) and the baroreceptor reflexes in the control of arginine vasopressin (AVP) secretion. Baroreceptor reflexes were activated by a 5- or 10-min period of bilateral carotid occlusion with or without background infusion of Ang II at 10 or 20 ng/kg.min. Carotid occlusion increased mean arterial pressure, right atrial pressure, and heart rate, but did not change plasma AVP (PAVP) concentration. Infusion of Ang II at 10 ng/kg.min increased PAVP from 4.0 +/- 0.9 to 6.3 +/- 1.8 pg/ml (P less than 0.05). Carotid occlusion during Ang II infusion produced the same cardiovascular changes as before Ang II, but still failed to increase PAVP. Because increased atrial pressure can inhibit AVP secretion, the experiments were repeated in acutely vagotomized rabbits. Vagotomy increased heart rate but did not change mean arterial pressure or PAVP. Carotid occlusion after vagotomy increased PAVP from 2.2 +/- 0.2 to 3.3 +/- 0.5 pg/ml (P less than 0.05). Ang II infusion again increased PAVP but did not enhance the AVP response to carotid occlusion (2.9 +/- 0.4 to 3.9 +/- 0.7 pg/ml). These results provide further evidence for a role of the carotid sinus baroreceptors and vagal afferents in the control of AVP secretion and demonstrate that Ang II stimulates AVP secretion in rabbits. However, they do not reveal any interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion.