Sex steroids do not alter melatonin secretion in the human

It is unclear whether sex steroids influence melatonin secretion in the human. In an attempt to find an answer to this important question 36 women within an age range of 19 to 40 years were studied within a 3-month period under the following conditions: natural menstrual cycle, ovulation induction with gonadotrophins, early pregnancy, and intake of monophasic or triphasic oral contraceptives. Except in the case of pregnancy, repeated measurements in the same individual were done because of the well-known large inter-individual variations in melatonin secretion. Melatonin concentration was measured in plasma samples obtained at 4-hourly intervals in a 24 h period and < 200 lux for all subjects studied. No consistent change in melatonin blood concentrations was demonstrated in response to the varying endogenous or exogenous concentrations of sex steroids. These observations suggest that circadian melatonin secretion is not significantly modulated by sex steroids.