Central vasopressin impairs the baroreceptor heart rate reflex in conscious rats

In conscious, unrestrained rats, the resting values of mean arterial blood pressure (BP) and heart rate (HR) as well as the baroreceptor heart rate reflex (BHR) were measured before and after intracerebroventricular (i.c.v.) application of arginine vasopressin (AVP). The BHR was induced by intravenous (i.v.) injection of different doses of phenylephrine. Basal values of BP and HR were 114 +/- 2.4 mm Hg and 376 +/- 13 beats/min (mean +/- SE). These values were not altered by i.c.v. application of vehicle or 5, 10, 30, 300, 3,000 pg AVP or 1 pg AVP antagonist [(D(CH2)5Tyr(Me)-AVP)]. Ten and 30 pg AVP administered i.c.v. attenuated the phenylephrine-induced decrease in HR. Lower or higher doses of AVP were not effective. Administration of the AVP antagonist i.c.v. sensitized the BHR. When the BHR was rechecked 24 h after treatment, the influence of the i.c.v.-administered peptides had disappeared. We conclude that AVP through the cerebrospinal fluid impairs the baroreflex regulation.