Actions of estradiol on the pulsatile secretion of bioactive luteinizing hormone in man

We evaluated the impact of estradiol on bioactive LH release in normal men by steady-state intravenous infusions of estradiol and oral administration of the antiestrogen tamoxifen HCl. The secretion of biologically active LH was monitored by the rat interstitial cell testosterone bioassay. Estradiol infusions decreased mean plasma bioactive LH concentrations and diminished the bio/immuno LH ratio. Conversely, the antiestrogen tamoxifen increased bioactive LH pulse frequency, bioactive LH pulse amplitude, and the plasma bio/immuno LH ratio. Exogenous injections of GnRH at 2-hr intervals also increased the bio/immuno LH ratio basally. However, tamoxifen attenuated the ability of exogenous GnRH to increase the bio/immuno LH ratio further, indicating attainment of maximal enrichment in LH bioactivity. These complementary observations on the impact of infused estradiol and exogenous antiestrogen indicate that estradiol modulates the pulsatile secretion of LH molecules enriched in biological activity in man.