The effect of haemorrhage and melatonin on neurohypophysial vasopressin and oxytocin content in pinealectomized male rats.

The effect of haemorrhage and melatonin on the vasopressin and oxytocin storage in the neurohypophysis of pinealectomized male rats was determined. Sham operated or pinealectomized rats as well as rats pinealectomized and injected with melatonin (100 micrograms/100 g b. w., once daily over 8 days) or with melatonin vehicle (2.2% ethanol in 0.9% NaCl) were subsequently subjected to haemorrhage. Pinealectomy was followed by known decrease of both vasopressin and oxytocin content in the neurohypophysis as compared to sham operated rats. Similarly, haemorrhage decreased the neurohypophysial vasopressin and oxytocin storage in both sham operated and pinealectomized animals. Melatonin, injected to pinealectomized animals, did not modify the diminution of neurohypophysial vasopressin and oxytocin content caused by bleeding. The results demonstrate that in pinealectomized rats melatonin does not affect the rate of the response of vasopressinergic and oxytocinergic neurones to bleeding.