[Diurnal beta-endorphin rhythm in relation to menstrual cycle phase]

Beta-endorphin (beta-EP) concentrations in hypophyseal portal blood are related to the menstrual cycle in primates. In women, changes in peripheral plasma beta-EP-concentrations were detected throughout the menstrual cycle. A similar circadian rhythm of beta-EP and ACTH was observed in males, suggesting a common mechanism of secretion at the pituitary level. We examined beta-EP, cortisol (F) and prolactin (PRL) levels in peripheral blood of regularly menstruating women. Samples were taken every 2 hours between 6 p.m. and 10 a.m. on days 3 and 4 of the menstrual cycle and 6 and 7 days after the rise of the basal body temperature. A diurnal rhythm of beta-EP could be seen between 6 p.m. and 10 a.m. in the luteal phase, but not in the follicular phase. An early morning rise of beta-EP was accompanied by increasing F-concentrations, suggesting a concomitant secretion of beta-EP and ACTH by the cells of the anterior pituitary. We therefore conclude, that ovarian steroids may influence beta-EP secretion at the pituitary level as well.