Vasoactive intestinal peptide (VIP) stimulates oxytocin and vasopressin release from the neurohypophyis

The concentration of vasoactive intestinal peptide (VIP) was measured by RIA in pituitary extracts of female cats; it was significantly higher in the posterior than in the anterior lobe, 47.3 +/- 3.9 pmol/g wet wt vs. 7.7 +/- 2.0 pmol/g wet wt (mean +/- SE, n = 5 in both instances). To investigate the effect of VIP on the release of posterior pituitary hormones, the concentration of arginine vasopressin and oxytocin was measured by RIA in jugular vein plasma during intracarotid infusion of VIP. The levels of both hormones rose during the 5-min infusion of VIP. Oxytocin levels increased from a mean of 7.9 microU/ml to a maximum of 34.9 microU/ml at 1 min and arginine vasopressin levels from from 27.4 microU/ml to a maximum of 157 microU/ml at 1 min. The levels of both hormones returned to baseline values in about 20 min. Since VIP has been localized to the nerve terminals of the neurohypophysis, these data suggest that endogenous VIP may play a role as a neurotransmitter in the magnocellular hypothalmo-neurosecretory system.