Estrogen Metabolism in the Human. III. A Comparison Between Females, Studied During the First and Second Halves of the Menstrual Cycle, and Males

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Abstract
Estrogen metabolism in females and males has been explored for possible differences between the sexes. Two female groups were studied, those in the first half (proliferative phase) of the menstrual cycle and those in the second half (secretory phase). These groups were compared with one another, and with a male group previously reported. Estradiol-17β,6,7-3H was administered, and the urinary excretion of radioactive estrone, estradiol-17β and estriol was determined, together with the simultaneous excretion of the corresponding endogenous (nonradioactive) estrogens. The interrelationship of radioactive and nonradioactive estrogens was studied by analysis of interaction. Specific activities and estradiol-17β production rates were calculated. Data for each group were fitted to a previously described mathematical model, designed to test the hypothesis that the 3 urinary estrogens are derived solely from estradiol-17β secreted into an inner pool. The interrelationship of the 3 radioactive estrogens was similar in both halves of the cycle, indicating no change in the metabolism of injected estradiol-17β,6,7-3H. The interrelationship of the 3 endogenous estrogens was significantly different, however. These findings indicate a change in the pattern of estrogen estrogen secretion between the 2 halves of the cycle. Analysis of the model indicated that estradiol-17β could be the principal precursor of the 3 urinary estrogens in the first half of the cycle, but not in the second half, further suggesting a change in the pattern of secretion. A significant difference in the metabolism of estradiol-17β,6,7-3H between females (both halves of the cycle) and males was established. Specific activities of the 3 estrogens were similar in females (1st half of cycle) and significantly different in males, suggesting a difference in the pattern of estrogen secretion (as well as of estrogen metabolism) between females in the first half of the cycle and males. A difference in the secretion pattern was further substantiated by the analysis of the model, which showed that the 3 urinary estrogens could be derived principally from estradiol-17β in the female (1st half of the cycle), but could not be so derived in the male. There was a significant difference in the interrelationship of the 3 endogenous estrogens between females (2nd half of the cycle) and males, also due probably to a difference in the pattern of estrogen secretion as well as of estrogen metabolism between these groups.

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