| Abstract: | The antidiuretic effects of intravenous (i.v.) and intracerebroventricular (i.c.v.) infusions of vasopressin (AVP) were compared in chronically cannulated conscious Brattleboro rats. AVP infused i.c.v. for 6 h reduced urine volume and increased urinary Na+ and K+ concentrations. These antidiuretic responses to i.c.v. AVP were dose related in the range 3-12 ng/h and were delayed and prolonged when compared with i.v. infusions (0.33-3 ng/h) of this peptide. Comparison of the dose-response curves for both routes of administration demonstrated that the antidiuretic response to i.c.v. infusion of AVP was approximately 10-fold lower than to AVP given intravenously. Since measurable amounts of AVP-like material appeared in the urine during the antidiuretic response, we conclude that a significant amount of AVP infused into the cerebroventricular system reaches the bloodstream in a biologically active form. |
