I. Kostoglouathanassiou et al., NEUROHYPOPHYSEAL HORMONE AND MELATONIN SECRETION OVER THE NATURAL ANDSUPPRESSED MENSTRUAL-CYCLE IN PREMENOPAUSAL WOMEN, Clinical endocrinology, 49(2), 1998, pp. 209-216
OBJECTIVE Vasopressin, oxytocin and melatonin have been reported to be
influenced by ovarian steroids. The neurohypophysial hormones have al
so been shown to display a diurnal pattern of secretion in men, We the
refore studied the diurnal pattern of neurohypophysial hormone and mel
atonin secretion in premenopausal women and in women on oral contracep
tives. DESIGN Healthy normally cycling premenopausal women were studie
d over 24 hours during the midfollicular and midluteal phases of the m
enstrual cycle. Healthy premenopausal women on oral contraceptives wer
e studied over 24 hours at similar times. SUBJECTS Eight healthy norma
lly cycling women and 7 healthy premenopausal women on oral contracept
ives. MEASUREMENTS Plasma vasopressin, oxytocin and melatonin were mea
sured by radioimmunoassay. RESULTS Vasopressin concentrations and its
nocturnal peak were highest in the follicular phase of the natural men
strual cycle and attenuated in the women on oral contraceptives, Oxyto
cin concentrations did not vary between the two phases of the menstrua
l cycle, but increased on oestrogen administration. Overall melatonin
secretion was augmented in the women on oral contraceptives. CONCLUSIO
NS Vasopressin release and its nocturnal peak were greatest in the fol
licular phase of the menstrual cycle, while melatonin secretion was au
gmented in the women on oral contraception.