Response of serum inhibin B and pro-αC levels to gonadotrophic stimulation in normal men before and after steroidal contraceptive treatment

Background: Testicular regulation of inhibin B may be influenced by the germ cell complement. Methods: We examined the effects of gonadotrophin stimulation on serum inhibin B and pro-αC in 25 normal men at (i) control (stimulation test 1), (ii) after spermatogenic suppression induced by testosterone plus progestin treatment (stimulation test 2), and (iii) during spermatogenic recovery induced by FSH and/or hCG treatment (stimulation test 3). For each test, subjects received a single injection of 1200 IU FSH or 5000 IU hCG or both. Results: Inhibin B and pro-αC fell with spermatogenic suppression (75 and 51% of pre-treatment baseline respectively, P <0.05). Inhibin B response to FSH (130-144%) was similar in controls and after germ cell suppression. Pro-αC response after germ cell suppression compared with control was significantly increased (P <0.05) with both FSH (210-229% versus 140-185%) and hCG (254-261% versus 145%). All treatments partially restored spermatogenesis with no clear relationship apparent between inhibin B and sperm count. Conclusions: We conclude that: (i) serum inhibin B and pro-αC are only partially gonadotrophin dependent, (ii) spermatogenic suppression does not modify inhibin B response to FSH but enhances pro-αC response to both FSH and hCG, and (iii) inhibin B is a poor marker of spermatogenesis in this model of gonadotrophic manipulation in normal men.