Effect of inhibition of estrogen synthesis during the luteal phase on function of the corpus luteum in rhesus monkeys.

It has been hypothesized that estrogen synthesized by the corpus luteum initiates luteal regression during the nonfertile menstrual cycle in primates. To study the role of endogenous estrogens in functional regression of the monkey corpus luteum, we administered the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD) to rhesus monkeys during the luteal phase of the menstrual cycle. Twice-daily oral administration of ATD suppressed systemic and intraluteal estrogen levels by 80-90%. The midluteal phase rise in estradiol concentrations that occurs in rhesus monkeys was completely abolished by ATD treatment. Despite suppression of estrogen synthesis during the luteal phase, mean menstrual cycle length and length of the luteal phase were not different than in control monkeys treated with vehicle only. Progesterone levels were lower in the ATD-treated group on the second and third day of treatment, but did not differ from control levels during the remainder of the cycle. These data suggest that elevated estrogen synthesis during the luteal phase of the menstrual cycle is not a prerequisite for spontaneous luteolysis in rhesus monkeys.