Reproductive hormones in menstrual blood

Menstrual and peripheral blood samples were collected from 19 regularly cycling women on days 1-3 of the menstrual cycle. Menstrual samples were collected with a soft silicone rubber menstrual cup. Hematocrit, PRL, LH, FSH, estradiol (E2), and progesterone (P4) were measured in all samples. Validation studies were carried out for RIAs of PRL, LH, and FSH in menstrual plasma. The menstrual plasma PRL level was significantly higher than its peripheral blood level on day 1 (63.3 +/- 14.7 and 12.1 +/- 2.9 micrograms/L, respectively; t = 3.331; P less than 0.01), and menstrual PRL was significantly higher on day 1 than on day 2 (t = 3.340; P less than 0.01). There was a strong negative correlation between log menstrual PRL concentration and time of onset of menstruation (r = -0.596; P less than 0.01). Menstrual plasma FSH levels were significantly lower than peripheral levels on each of days 1-3 (day 1:t = 4.787; P less than 0.001), and there was a significant positive correlation between menstrual and peripheral levels (r = 0.607; P less than 0.01). By contrast, menstrual plasma LH was significantly higher than the peripheral level on days 1 and 2 (day 1:t = 3.105; day 2:t = 3.180; P less than 0.01), with no correlation between menstrual and peripheral levels. Menstrual E2 was slightly lower than and significantly positively correlated with peripheral E2 (r = 0.646; P less than 0.01). Menstrual P4 was lower than but showed no correlation with peripheral levels. As expected, the menstrual blood hematocrit was less than 0.20 and highly significantly lower than that of peripheral venous blood. These results suggest that PRL is released in substantial amounts from secretory endometrium into the menstrual flow during the first day of menstrual breakdown. LH may also be released in small amounts from menstrual endometrium, while menstrual FSH, E2, and P4 probably arise entirely from the peripheral circulation.