Spinal vasopressin mechanisms of cardiovascular regulation.

Extrahypothalamic vasopressin-containing neurons have been implicated in the central neural control of the cardiovascular system. In the present study we investigated the possibility that vasopressinergic neurons arising from the paraventricular nucleus (PVN) and terminating in the spinal cord are involved in the regulation of vasomotor functions. Vasopressin (1-17 pmol) was injected into the spinal subarachnoid space of conscious rats instrumented with Doppler flow probes and indwelling intrathecal catheters. The peptide produced a dose-related increase in arterial pressure accompanied by vasoconstriction in the mesenteric, renal, and hindquarter vascular beds. Pretreatment, intrathecally, with 0.5 nmol of the vasopressin antagonist d(CH2)5Me(Tyr)AVP completely prevented the increase in arterial pressure expected after subsequent intrathecal injection of vasopressin. However, the changes in arterial pressure and vascular resistances produced by stimulation of the PVN were not affected by the intrathecal antagonist. Stimulation of the PVN in Brattleboro rats, which lack hypothalamic and spinal vasopressin, produced hemodynamic responses similar to those produced in Long-Evans control rats. Taken together, these data suggest that spinal vasopressin can act within the spinal cord to alter vasomotor functions; however, the hemodynamic effects evoked by stimulation of the PVN do not appear to depend on spinal vasopressinergic mechanisms.