Premature elevation of systemic estradiol reduces serum levels of follicle-stimulating hormone and lengthens the follicular phase of the menstrual cycle in rhesus monkeys.

The concentration of estradiol in peripheral serum was prematurely elevated on days 3-6 of the rhesus monkey menstrual cycle to approximate the estradiol rise typically seen during the midfollicular phase. Associated with an estradiol increase (from 60 to approximately 90 pg/ml) was a significant (P less than 0.01) reduction in FSH levels and a lengthening of the follicular phase of the menstrual cycle. These results reveal the existence of an exquisitely sensitive negative feedback relationship between estradiol and FSH during the follicular phase of the menstrual cycle, in doing so, these findings suggest that the selected follicle, by way of its secretion of estradiol, indirectly inhibits the maturation of other follicles by reducing gonadotropin levels.