Enhancement of gonadotrophin induced 17,20-lyase suppression one week after human chorionic gonadotrophin priming.

A single injection of 1500 IU of human chorionic gonadotrophin (hCG) in normal men, induced a block in the conversion of 17-hydroxyprogesterone (17-OHP) to testosterone (T) which reached its maximum 24 h after hCG loading. One week after hCG administration both basal 17-OHP (3.8 +/- 0.6 vs 5.1 +/- 0.5 nmol/l, P less than 0.02) and T levels (15.1 +/- 1.7 vs 18.5 +/- 2.3 nmol/l, P less than 0.05) were about 20% lower than before hCG exposure. The ratio 17-OHP to T (0.29 +/- 0.04 vs 0.31 +/- 0.04, P greater than 0.10) was however similar, suggesting recovery from the prior 17,20-lyase suppression at a lower overall capacity of T synthesis. hCG administration one week after the priming dose elicited an increase in the ratio 17-OHP to T, which was about twice as high as after the first hCG injection. Together the data suggest: 1) suppression of testicular steroidogenesis proximal to 17-OHP one week after hCG priming, 2) enhanced hCG induced 17,20-lyase suppression one week after hCG exposure.