Testosterone suppression of the HPT axis

Although studies have demonstrated the suppression of normal gonadal function in the experimental setting, the specific mechanisms by which androgenic-anabolic steroids impact male gonadal function remain ill defined. Following 2 consecutive weekly injections of an identically appearing testosterone cypionate (TC) placebo, subjects were randomized to a TC dose of 100 mg/wk, 250 mg/wk, or 500 mg/wk. Following the last weekly injection of active agent the subjects received 12 consecutive weeks of TC placebo injections.

Spermatogenesis was impaired by each of the doses of TC employed in this study, but the observed decreases in, sperm count were neither strictly dose dependent nor consistent between individuals treated with the same dose. Basal leuteinizing hormone (LH) and follicle stimulating hormone (FSH) became undetectable 2 weeks after the start of 250 and 500 mg/wk TC injections and were lost within 5 to 6 weeks of starting 100 mg doses. Pituitary gonadotropin responses to leutinizing hormone releasing hormone (LHRH) disappeared more slowly with FSH responses being lost 1 to 3 weeks after the loss of basal FSH activity. Leuteinizing hormone responses to LHRH appeared to be suppressed last, disappearing 4 to 6 weeks after FSH responses to LHRH.

Exogenous testosterone-mediated inhibitory influences on the hypothalamic-pituitary-testicular axis were reversed following the cessation of drug treatment.