Vasopressin and oxytocin modulation of melatonin secretion from rat pineal glands.

The rat pineal gland is known to release melatonin in response to noradrenergic stimulation. Since vasopressin (VP)- and oxytocin (OT)-containing fibers innervate the pineal gland, the effects of VP and OT on melatonin release from perifused rat pineal glands were investigated. VP (10(-7) M) and OT (10(-6) M) decreased the basal melatonin secretion. No dose-dependent effect was observed. At high concentrations (10(-5)) these peptides potentiated the isoproterenol-induced increase of melatonin secretion. Below 10(-5) M no potentiation was observed. Fragments of VP ([pGlu4,Cys6]VP(4-9] and OT (pGlu4,Cys6]OT(4-9] did not display any effect on the isoproterenol-induced melatonin secretion.