Response of serum inhibin B and pro-alphaC 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. Method(s): We examined the effects of gonadotrophin stimulation on serum inhibin B and pro-alphaC 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. Result(s): Inhibin B and pro-alphaC 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-alphaC 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. Conclusion(s): We conclude that: (i) serum inhibin B and pro-alphaC are only partially gonadotrophin dependent, (ii) spermatogenic suppression does not modify inhibin B response to FSH but enhances pro-alphaC 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.