ROLES OF THE SUPRACHIASMATIC NUCLEUS AND VASOACTIVE-INTESTINAL-PEPTIDE IN THE RESPONSE OF PLASMA ARGININE-VASOPRESSIN TO OSMOTIC CHALLENGE

To clarify the role of neurons containing a vasoactive intestinal pept ide (VIP)-like substance (VIP neurons) in the hypothalamic suprachiasm atic nucleus (SCN) in regulation of the plasma arginine vasopressin (A VP) concentration, we examined the effects of bilateral lesions of the SCN and intracranial injection of VIP on the increase in the plasma A VP concentration caused by ip injection of hypertonic (3.6%) saline in rats. The increase in the plasma AVP concentration after ip injection of hypertonic saline was significantly suppressed in rats with bilate ral lesions of the SCN. Furthermore, the increase in the plasma AVP co ncentration elicited by ip injection of hypertonic saline was enhanced by intracerebroventricular injection of VIP and suppressed by a VIP a ntagonist, [Lys1,Pro(2,5),Arg(3,4),Tyr(6)]VIP. However, the same dose of VIP injected into the heart had no effect on the increase in the pl asma AVP concentration caused by ip injection of hypertonic saline. Th ese results suggest that the SCN and intracranial VIP play important r oles in the regulation of the plasma AVP concentration and support the possibility that VIP neurons in the SCN enhance the response of plasm a AVP to osmotic challenge.