Regulation of human gonadotropins. VIII. suppression of serum LH and FSH in adult males following exogenous testosterone administration

Serum LH and FSH levels were measured by radioimmunoassay after exogenous testosterone was administered to four groups of adult males in dosages ranging from 1-25 mg per day. Serum testosterone concentrations, determined by radioimmunoassay, were elevated subsequent to the administration of the higher dosages. Dose-related depression of both LH and FSH was observed subsequent to administration of 5 or more mg of testosterone per day; the smallest dosage (1 mg) was not associated with any consistent changes in LH or FSH. The rate and extent of decline of the two gonadotropins differed. Serum LH values tended to drop and recover more rapidly than FSH following testosterone administration. These results indicate that testosterone suppresses serum levels of both LH and FSH in the human adult male. There was no evidence of stimulation of gonadotropin release at these doses.