Specific Regulatory Actions of Dihydrotestosterone and Estradiol on the Dynamics of FSH Secretion and Clearance in Humans

The authors investigated immunoactive and bioactive follicle‐stimulating hormone (FSH) secretion and clearance in six healthy young men during steady‐state infusions of vehicle (basal, B, 28 hours), dihydrotestosterone (DHT, 4.5 days), or estradiol (4.5 days) accompanied by blood sampling at 10‐minute intervals for 28 hours. Serum FSH concentrations were assayed by a two‐site immunoradiometric assay (IRMA) and two separate in vitro bioassays (rat granulosa and Sertoli cell systems). FSH measurements included: 24‐hour mean serum concentrations (IRMA and bioassay), multiple‐parameter deconvolution of 24‐hour pulsatile FSH time series and FSH release in response to exogenous gonadotropin‐releasing hormone (GnRH) boluses (IRMA) to assess secretion and clearance, and circadian serum FSH concentration rhythms by cosinor analysis (IRMA). We found: 1) a significant decrease in 24‐hour mean IRMA FSH concentrations during DHT infusion while both in vitro estimates of FSH bioactivity were unchanged; 2) significant decreases in the mass of IRMA FSH secreted per 24 hours during DHT infusion; 3) significant decreases in the IRMA FSH half‐life during estradiol infusion without any change in FSH interpulse interval; 4) no steroidal effects on FSH secretory responses to exogenous GnRH; and 5) abolition of basal circadian FSH rhythms during sex‐steroid infusions. Based on these findings, we conclude that steady‐state sex‐steroid hormone infusions selectively alter IRMA FSH secretion and clearance without affecting IRMA FSH pulse frequency or mean concentrations of bioactive FSH. 1991 American Society of Andrology