Reversal by arginine-vasotocin of the effects of pinealectomy on the amount of 5-hydroxytryptamine in the hypothalamus and the concentrations of luteinizing hormone and follicle-stimulating hormone in the plasma of immature male rats.

Pinealectomy in immature (25-day-old) male Wistar rats significantly decreased the content of 5-hydroxytryptamine (5-HT) in the hypothalamus and increased concentrations of plasma LH and FSH 3 days after surgery. Extremely small amounts (10(-4) pg) of arginine-vasotocin (AVT) injected into the third ventricle (pineal recess) 5 min after pinealectomy completely prevented the decrease in the hypothalamic content of 5-HT and the increase in the concentration of LH and FSH in the plasma. It is suggested that AVT prevented the increase of plasma levels of LH and FSH after pinealectomy by increasing levels of 5-HT at postsynaptic receptor sites.