TESTOSTERONE SUPPRESSION OF THE HPT AXIS

Background: Although studies have demonstrated the suppression of norm al gonadal function in the experimental setting, the specific mechanis ms by which androgenic-anabolic steroids impact male gonadal function remain ill defined, Methods: Following 2 consecutive weekly injections of an identically appearing testosterone cypionate (TC) placebo, subj ects were randomized to a TC dose of 100 mg/wk, 250 mg/wk, or 500 mg/w k, Following the last weekly injection of active agent the subjects re ceived 12 consecutive weeks of TC placebo injections, Results: Spermat ogenesis was impaired by each of the doses of TC employed in this stud y, but the observed decreases in sperm count were neither strictly dos e dependent nor consistent between individuals treated with the same d ose, Basal leuteinizing homone (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 dos es, Pituitary gonadotropin responses to leutinizing homone releasing h omone (LHRH) disappeared more slowly with FSH responses being lost 1 t o 3 weeks after the loss of basal FSH activity, Leuteinizing hormone r esponses to LHRH appeared to be suppressed last, disappearing 4 to 6 w eeks after FSH responses to LHRH. Conclusions: Exogenous testosterone- mediated inhibitory influences on the hypothalamic-pituitary-testicula r axis were reversed following the cessation of drug treatment.