Melatonin inhibits the substance P-induced secretion of vasopressin and oxytocin from the rat hypothalamo-neurohypophysial system: In vitro studies

Abstract

The aim of the present investigations was to study the influence of substance P (a member of a family of peptides known as tachykinins) on basal and K +-evoked vasopressin (AVP) and oxytocin (OT) release from rat hypothalamo-neurohypophysial system in vitro as well as to determine whether this effect of substance P is sensitive to melatonin. The present results show that substance P stimulates basal AVP and OT release from isolated hypothalamo-neurohypophysial system, when used at the concentrations of 10 −6 and 10 −7 M/l. At the concentration of 10 −9 M/l, however, substance P was found to stimulate the in vitro secretion of AVP, but not that of OT. Melatonin diminished basal release of AVP; it also significantly inhibited the substance P-stimulated secretion of AVP and OT. K +-evoked release of the neurohypophysial hormones was not further modified by either substance P or melatonin. The present results show that the stimulatory effect of substance P on basal release of AVP and OT from rat hypothalamo-neurohypophysial system in vitro is sensitive to inhibitory influence of melatonin.