Circadian hormonal interactions among the mother, fetus, and amniotic fluid.

Circadian rhythms and hormonal interactions among the maternal, fetal, and amniotic fluid compartments were studied in long-term catheterized rhesus macaque monkeys between days 127 and 138 of gestation (term = 167 days). Blood samples were collected at 3-hour intervals for 48 hours and analyzed by radioimmunoassay for estrone, estradiol, cortisol, progesterone, dehydroepiandrosterone sulfate, and prolactin. Distinct circadian rhythms were present for cortisol and progesterone in the maternal circulation and for progesterone and dehydroepiandrosterone sulfate in the fetal circulation (p less than 0.05). Although maternal and fetal estrogen levels were higher in AM samples than in PM samples, a statistically significant circadian rhythm was not present (p greater than 0.10). Fetal levels of progesterone and dehydroepiandrosterone sulfate and maternal levels of progesterone were highest between 9:00 PM and 3:00 AM and lowest between 9:00 AM and 3:00 PM. Maternal levels of cortisol were highest between 6:00 AM and 9:00 AM and lowest between 6:00 PM and 12 midnight. The circadian patterns of maternal cortisol and progesterone were inversely related to each other (r = -0.68; p less than 0.01). Amniotic fluid cortisol levels were highest between 9:00 AM and 12 noon and lowest between 6:00 PM and 3:00 AM (p less than 0.10). With the possible exception of cortisol, amniotic fluid steroid hormones did not demonstrate distinct diurnal fluctuations, nor did they correlate with steroid changes in maternal or fetal blood. Because the rhesus placenta is permeable to glucocorticoids it is likely that transplacental passage of maternal cortisol influences the activity of the fetal pituitary and adrenal so that the circadian rhythm in the fetal axis is 180 degrees out of phase with that of the maternal axis. The circadian rhythms in fetal dehydroepiandrosterone sulfate and progesterone in late gestation parallel the biorhythm in uterine contraction frequency and amplitude, with peaks during periods of darkness between 9:00 PM and 3:00 AM.