ENHANCED PRESSER RESPONSES TO ICV VASOPRESSIN AFTER PRETREATMENT WITHOXYTOCIN

The role of oxytocin (OT) in the modulation of arginine vasopressin (A VP)-induced cardiovascular effects within the central nervous system w as investigated in urethan-anesthetized rats. Intracerebroventricular injection of AVP (1-10 pmol) produced dose-dependent increases in mean arterial pressure (MAP) and heart rate (HR). These responses were enh anced in rats pretreated 24 h earlier with OT (10 pmol icv). The enhan ced cardiovascular effects of AVP in OT-pretreated animals were dose d ependent, blocked by the V-1 antagonist d(CH2)(5)Tyr(Me)AVP, not evoke d by OT alone, and occurred in the absence of changes in basal (nonsti mulated) MAP and HR. In addition, central administration of AVP in OT- pretreated rats, but not in saline-pretreated controls, caused dose-de pendent oscillations of the MAP and HR responses and, at higher doses, death of the animals. The enhanced cardiovascular actions of centrall y injected AVP in OT-pretreated rats do not appear to be secondary to skeletal muscle contractions or the result of cerebral ischemia. Our d ata point to an interaction between the central oxytocinergic and vaso pressinergic systems in cardiovascular control.