Dissociated responses of plasma testosterone and 17-hydroxyprogesterone to single or repeated human chorionic gonadotropin administration in normal men.

After both single (1500 IU) and daily repeated (1500 IU daily for 3 days) im administration of hCG, peak values of 17-hydroxyprogesterone (17OHP) were achieved 24 h after the single or first injection, whereas plasma testosterone (T) levels reached their maximum 48 h later. After the peak value of 17-OHP at 24 h, both steroids ran dissociated courses with the T levels rising and the 17-OHP levels falling. In both the single and repeated hCG experiments, the initial rise of 17-OHP was more pronounced than that of T, leading to a steep temporary increase of the 17-OHP to T ratio in the first 24 h. Repeated hCG administration for 3 days to the same subjects elicited T responses at 48 and 72 h quantitatively similar to those produced by single hCG loading, although the 17-OHP response appeared slightly higher in the multiple dose experiment. The data indicate that exogenous gonadotropins may influence testicular steroidogenesis not only quantitatively, but also qualitatively, possibly by altering enzyme activities.