Human platelet monoamine oxidase and the menstrual cycle

Endocrine factors are known to affect platelet monoamine oxidase (MAO) activity. To assess the role of sex steroid hormones in regulating MAO, blood samples for platelet MAO assay were obtained twice weekly from 12 women. Peak MAO activity occurred during the ovulatory interval and a nadir occurred in the postovulatory phase, 5 to 6 days later. A 17% mean effect of menstrual variation from peak to nadir was noted. The implications for MAO studies in psychiatric research are discussed.