Beta-endorphin levels in the human menstrual cycle

To examine the fluctuation in plasma beta-Endorphin (beta-EP) concentration throughout the menstrual cycle, 8 healthy females with normal cycles were studied. After an overnight fast, the subject's blood samples were drawn between 8 and 10 a.m. They gave blood at 2 or 4 day intervals through three menstrual cycles. Using the LH surge as day 0, the mean beta-EP concentrations were higher on days -10, -9, -8 (6.5 +/- 2.6, 6.9 +/- 3.8 and 6.7 +/- 2.7 pmol/l, follicular phase), on days -1, 0, +1 (9.2 +/- 3.3, 9.1 +/- 5.2 and 8.8 +/- 3.3 pmol/l, periovulatory phase), and on days +9 and +12 (8.6 +/- 2.5 and 8.8 +/- 3.8 pmol/l, luteal phase). Most beta-EP levels were low during menstruation. The rise and fall in beta-EP and its relation to temporal LH and FSH secretion are discussed. The findings show that three beta-EP rises take place during the menstrual cycle and that beta-EP may be involved in the regulation of ovulation.