Prolonged biphasic response of plasma testosterone to single intramuscular injections of human chorionic gonadotropin.

The response of plasma testosterone to varying doses of hCG (0--6000 IU) given as a single im injection has been evaluated in normal men. After an initial rise at 2 h, the levels of testosterone demonstrated a secondary rise, reaching a peak 48 h after the im injection. The magnitude of the response varied directly with the dose of hCG used, and at the highest dose (6000 IU) testosterone levels were still elevated 6 days after administration. Plasma estradiol levels showed a dose-dependent rise, with peak levels being attained 24 h after hCG. The prolonged response of plasma testosterone to a single injection of hCG should prompt a reevaluation of diagnostic and therapeutic regimens using this agent.