Melatonin- and serotonin-stimulated release of vasopressin from rat neurohypophysis in vitro

Abstract

In order to study the control of vasopressin-release, the effect of a series of potential agents was studied in an in vitro perifusion system of rat neurohypophysis after in vivo treatment with nialamide, a monoamine oxidase inhibitor. In this system, metlatonin stimulated vasopressin-release in a dose-dependent manner (1 × 10 −8 to 1 × 10 −3 M). Serotonin (1 × 10 −3 M) also led to a significant increase of vasopressin-release whereas quipazine (1 × 10 −3 M), a putative serotonin agonist and monoamine oxidase inhibitor, caused a 3-fold stimulation of the release of the neurohormone. The stimulatory effects of melatonin and serotonin were prevented by omission of Ca 2+ combined to an excess of Mg 2+ (12 mM) in the perifusion medium. 1 × 10 −6 M somatostatin did not affect basal or melatonin-stimulated vasopressin-release. These results show that melatonin and serotonin can have a direct stimulatory effect on vasopressin release at the neurohypophyseal level.