Reduced Serum Inhibin Concentrations During Ovulatory Cycles of Estrogen-Treated Rhesus Monkeys: An Indicator of FSH Bioactivity

Female rhesus monkeys treated with exogenous estrone initially were anovulatory. Although estrone and estradiol concentrations were maintained 1.5- to 2.5-fold elevated, i.e. in the midfollicular range, ovulatory cycles resumed in three of four animals after 6–15 months of anovulation. During the ovulatory cycles the serum bio LH concentrations were the same in estrone-treated animals as during ovulatory cycles of control monkeys, but the daily basal serum FSH concentrations detectable by RIA were significantly reduced during the ovulatory cycles of the estrone-treated animals compared to the cycles of the controls. In the present study serum inhibin concentrations were measured to determine whether or not they were increased and the cause of the selective decrease in FSH concentrations in the estrogen-treated monkeys. Serum LH, FSH, progesterone, and inhibin concentrations were measured by RIA in blood samples collected during the third year of continuous estrogen treatment. The lack of an effect of elev...