Neurohypophysial hormone and melatonin secretion over the natural and suppressed menstrual cycle in premenopausal women.

Abstract

Vasopressin, oxytocin and melatonin have been reported to be influenced by ovarian steroids. The neurohypophysial hormones have also been shown to display a diurnal pattern of secretion in men. We therefore studied the diurnal pattern of neurohypophysial hormone and melatonin secretion in premenopausal women and in women on oral contraceptives. Healthy normally cycling premenopausal women were studied over 24 hours during the midfollicular and midluteal phases of the menstrual cycle. Healthy premenopausal women on oral contraceptives were studied over 24 hours at similar times. Eight healthy normally cycling women and 7 healthy premenopausal women on oral contraceptives. Plasma vasopressin, oxytocin and melatonin were measured by radioimmunoassay. Vasopressin concentrations and its nocturnal peak were highest in the follicular phase of the natural menstrual cycle and attenuated in the women on oral contraceptives. Oxytocin concentrations did not vary between the two phases of the menstrual cycle, but increased on oestrogen administration. Overall melatonin secretion was augmented in the women on oral contraceptives. Vasopressin release and its nocturnal peak were greatest in the follicular phase of the menstrual cycle, while melatonin secretion was augmented in the women on oral contraception.