Diurnal rhythms of labor and delivery in women: modulation by parity and seasons.

Objectives: Our purpose was to evaluate in women the diurnal (24 hour) rhythms of the onset of labor and time of delivery and their modulation by parity and seasons.

Study Design: A retrospective analysis was performed on 15,910 at term deliveries of single fetuses with noninduced labor.

Results: A diurnal rhythm of labor onset, with peak frequency at 8 PM and 9 AM was observed in nulliparous women but not in multiparous women.

Melatonin enhances cortisol levels in aged women: reversible by estrogens.

The administration of melatonin increases cortisol levels in postmenopausal women. Aging and hypoestrogenism are believed to impair the regulation of the hypothalamo-pituitary-adrenal axis and may participate in the determination of this altered response. In this study the implications of hypoestrogenism were tested.

Contemporaneous melatonin administration modifies the circadian response to nocturnal bright light stimuli.

We investigated whether the contemporaneous administration of melatonin can modify circadian phase shifts induced by bright light stimuli. After a baseline evaluation, 10 women were exposed for three consecutive nights to a 4-h bright light stimulus (>3,000 lx) initiated at the time of the estimated core body temperature (BT(c)) nadir. Along with light, each woman orally received, randomly and in a double-blind fashion, placebo (n = 5) or melatonin (n = 5; 1 mg 30 min before and 0.

Modification of circadian body temperature rhythm during the luteal menstrual phase: role of melatonin.

In women during early follicular phase (FP), the rise of melatonin at night accounts for 40% of the nocturnal core body temperature (Tc) decline. In seven normal-cycling women, the circadian rhythms of Tc and melatonin of the FP were compared with those of the luteal phase (LP). In addition, in both phases the Tc response to daytime melatonin administration was investigated.

Melatonin enhances cortisol levels in aged but not young women.

In spite of animal data showing an effect of melatonin in the regulation of the hypothalamus-pituitary-adrenal (HPA) axis, no effect of melatonin on cortisol has been evidenced in young men. Gender and aging are believed to influence the regulation of the HPA axis, and may thus modulate the melatonin effect on cortisol. In this study we investigated whether an effect of melatonin on cortisol can be observed in women of different age.