Melatonin inhibits spontaneous and VIP-induced vasopressin release from suprachiasmatic neurons.

We have studied melatonin effects on vasopressin release from dispersed cells of the rat suprachiasmatic nuclei (SCN). The release follows a circadian rhythm peaking during the day and decreasing at night. Melatonin inhibits the spontaneous increase and accelerates the decrease of vasopressin release. Melatonin also inhibits vasopressin release induced by vasoactive intestinal peptide (EC50=0.4 nM). The inhibition of vasopressin release correlates with the known inhibitory effect of melatonin on spontaneous neuronal activity in SCN.