Possible Interaction: Oxytocin and Thyrotropin-Releasing Hormone

“ OT did not produce any effect on basal serum TSH and PRL levels and on the TRH-stimulated TSH secretion, whereas it significantly enhanced the PRL response to TRH.”

“This effect, however, is opposed: TRH acts as a stimulator of vasopressin biosynthesis most of all in young male rats and as an inhibitor for oxytocin biosynthesis especially in mature animals.”

“Since … thyrotropin-releasing hormone (TRH) can modulate the processes … vasopressin (AVP) and oxytocin ( OT ) biosynthesis and release mainly at the hypothalamo-neurohypophysial level, the present experiments were undertaken to estimate whether TRH, administered intravenously in different doses, modifies these mechanisms under conditions of osmotic stimulation, brought about by dehydration.”

“Under conditions of equilibrated water metabolism TRH diminished significantly the hypothalamic and neurohypophysial AVP and OT content but was without the effect on plasma oxytocin level; however, TRH in a dose of 100 ng/100 g b.w.”

“Under the same conditions, injections of TRH were followed by a significant decrease of plasma OT level.”

“On the contrary, in not suckled females TRH increased OT plasma concentration.”

“Simultaneously, TRH inhibited OT release into the blood plasma.”

“ TRH increased the hypothalamic as well as neurohypophysial OT content during suckling.”

“A direct effect of the TRH involved a diminishing of the nucleoli size in oxytocin cells.”

“Treatment with TRH resulted in significantly decreased hypothalamic oxytocin content in both euhydrated (i.e. given tap water ad libitum) and salt-loaded rats.”

“ TRH was 5-10 times more potent than OT on a molar basis.”

“In rats deprived of water for two days TRH completely prevented the decrease of neurohypophysial oxytocin due to stimulation of osmoreceptor origin.”

“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.”

“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, 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.”

“However, TSH secretion by cultures treated simultaneously with TRH and oxytocin could be suppressed to approximately half of that released by cells incubated with TRH alone.”