OBJECTIVES: It has been well-documented that serum melatonin levels are insensitive to estrous or menstrual ovarian steroid variations in the female rat or the human. However, a negative coupling has been already demonstrated between the nocturnal serum melatonin peak and serum E2 concentration during the late premenopausal period in the woman. The objection of the present study was designed to determine if diurnal serum melatonin values can be also lowered by a single administration of estrogen.
METHODS: We performed a detailed analysis of variations of serum estradiol, LH, FSH, melatonin and cortisol after one single I.M. injection of 2 mg of a conjugated estrogen, delestrogen (estradiol valerate) in 0.1 ml of oil. A 15 ml blood collection was done at 8:00 a.m. before the injection, and at 8:30 a.m., 9:00 a.m., 10:00 a.m., 12:00 noon, and 4:00 p.m. 17beta-estradiol, LH and FSH were determined by microparticle enzyme immunoassays kits. Melatonin determination was made using a RIA kit and cortisol was assayed by a RIA method.
RESULTS: A significant rise in serum 17beta-estradiol was already seen by one hour after the injection of estradiol valerate. Then, an almost linear increase was observed up to at last eight hours after the injection of estradiol valerate. A significant decrease in serum LH was not seen before four hours after the injection of estradiol valerate. Overall, there was a trend toward a decline in serum melatonin and cortisol concentration. The decreasing trend of cortisol serum level was tested as significant over time (p< 0.001). However, the decrease in serum concentration did not reach a significant level for melatonin.
CONCLUSION: Overall, these results show that after menopause an acute administration of estrogen during the early diurnal period of the day leads to a significant rapid decrease in cortisol serum values, but to only a partial non significant decrease in melatonin serum values.