The paraventricular nucleus and cardiovascular regulation: role of spinal vasopressinergic mechanisms.

In the present investigation we sought to determine whether spinal vasopressin or oxytocin of hypothalamic origin contributes to cardiovascular regulatory mechanisms. Exogenous vasopressin or oxytocin was injected into the spinal subarachnoid space of conscious, freely moving rats. Oxytocin had no effect on heart rate or blood pressure. However, vasopressin produced a marked increase in arterial pressure and a modest bradycardia. Previous intrathecal injection of a specific V1 vasopressin receptor antagonist completely prevented the haemodynamic effects expected after subsequent intrathecal injection of vasopressin. On the other hand, the increase in blood pressure and heart rate produced by stimulation of the paraventricular nucleus (PVN) was not prevented by the intrathecal antagonist. These data suggest that vasopressin can act specifically on spinal receptors to influence cardiovascular parameters. However, these spinal receptors do not appear to be functionally involved in the haemodynamic response produced by stimulation of the PVN.