Cardiovascular effects of intracerebroventricular injection of vasopressin in unanaesthetized normotensive and DOCA-salt hypertensive rats

The mean arterial pressure (MAP) and heart rate (HR) responses to intracerebroventricular (i.c.v.) administration of arginine vasopressin (AVP) in unanaesthetized normotensive control and DOCA-salt hypertensive rats were studied. Intracerebroventricular administration of AVP (0.25-1000 ng) to control rats produced dose-dependent long-lasting increases in MAP (5-45 mmHg) and HR (35-110 beats/min). Peripheral treatment of rats with an antipressor AVP antagonist had no effect on i.c.v. AVP-induced increases in MAP and HR, whereas the responses were blocked by i.c.v. administration of the antagonist. Peripheral administration of phentolamine and propranolol also completely blocked the changes in MAP and HR. DOCA-salt hypertensive rats showed significantly greater increases in MAP and HR in response to i.c.v. AVP and a tenfold lower threshold for stimulation. The results demonstrate that AVP acting on central neural structures can produce increases in MAP and HR by stimulating sympathetic outflow. Increased sensitivity and responsiveness to i.c.v. AVP in hypertensive rats suggest a potential mechanism of action of AVP in hypertension.