Monoamine oxidase (MAO) is a major enzyme in the catabolism of brain biogenic amines. Platelet MAO activity has been shown to be largely under genetic control. Animal studies, however, have suggested that endocrine factors may contribute to the nongenetic component of the variance in MAO activity between individuals.
To evaluate the possible effects of sex steroid changes on platelet MAO activity, blood samples for platelet MAO assay and plasma estradiol and progesterone levels were obtained twice weekly from 13 women. Peak MAO activity occurred during the ovulatory interval, and a nadir occurred 5 to 11 days later. The mean effect of the menstrual cycle-related variation was 23%. No statistically significant relationship was observed between platelet MAO activity and a global scale of menstrual mood variation.
Belmaker RH, Murphy DL, Wyatt RJ, Loriaux DL. Human Platelet Monoamine Oxidase Changes During the Menstrual Cycle. Arch Gen Psychiatry. 1974;31(4):553–556. doi:10.1001/archpsyc.1974.01760160093019