Thyrotropin-releasing hormone (TRH) and vasopressin and oxytocin release: in vitro as well as in vivo studies

Abstract

Rats euhydrated and dehydrated for two or four days were given intracerebroventricularly (i.c.v.) thyrotropin-releasing hormone (TRH) in a daily dose of 200 ng dissolved in 10 microliters of 0.9% sodium chloride.) A single dose of TRH administered to euhydrated animals was followed by a significant increase of the vasopressin content in the neurohypophysis and hypothalamus as well as of the hypothalamic oxytocin content. On the contrary, a single dose of TRH decreased the oxytocin content in the neurohypophysis. Under conditions of dehydration TRH distinctly restrained the decrease of vasopressin and oxytocin in the hypothalamus. In animals dehydrated for two or four days the decrease of oxytocin in the neurohypophysis, brought about by stimulation of osmoreceptors, was distinctly more marked under treatment with TRH. On the contrary, the depletion of neurohypophysial vasopressin was significantly less apparent under such conditions. 28 nmol/L TRH markedly increased vasopressin release but inhibited that of oxytocin from the neurointermediate lobes incubated in vitro both under basal conditions as well as during stimulation with excess (56 mmol) potassium.