Luteinizing hormone bioactivity in human menopausal gonadotropin/human chorionic gonadotropin-induced cycles.

Eight human menopausal gonadotropin/human chorionic gonadotropin (hMG/hCG)-induced cycles in four anovulatory women unresponsive to clomiphene citrate plus hCG were studied. Blood samples were obtained for baseline determinations and daily thereafter, 24 hours after the injection of hMG. Serum estradiol (E2), progesterone, follicle-stimulating hormone, and luteinizing hormone (LH) were measured by radioimmunoassay. Bioassayable LH (LH-b) was determined by the immature mice interstitial cell in vitro bioassay for testosterone with LER-907 as the reference standard. Appropriate follicular growth, assessed by pelvic ultrasonography, occurred in all cycles. During induction days mean immunoassayable LH (LH-i) and LH-b levels were suppressed until the E2 concentrations rose to a mean of 1420.5 +/- 149 pg/ml (standard error of the mean), at which time a concurrent rise in LH-b and LH-i levels was observed (130% and 34%, respectively). LH-b/LH-i ratio increased by 63% on the day E2 peaked, indicating enhanced LH bioactivity before hCG administration. Our data suggest that during hMG/hCG-induced cycles, in a high E2 milieu, endogenous or exogenous LH may show a heterogeneity in its molecular content, resulting in enhanced bioactivity relative to immunoactivity.