Inverse relationship between serum inhibin B and FSH levels in prepubertalboys with cryptorchidism

To investigate the gonadal control of FSH secretion in prepuberty, we studi ed the relationship between circulating inhibin B and FSH levels in 16 prep ubertal boys with cryptorchidism (age range, 1-8 y). The effect of Leydig c ell stimulation on the secretion of inhibin B, sex steroids, and FSH was in vestigated in nine boys who were given human chorionic gonadotropin (hCG) t reatment. In these boys, serum inhibin B, testosterone, estradiol, and gona dotropin levels were measured before and on the fourth day of the last (thi rd) hCG injection, given at l-wk intervals. Except for one boy with both hi gh inhibin B and FSH concentrations, basal serum levels of these hormones c orrelated negatively (r(S) = -0.79, it = 15,p < 0.005). This inverse relati onship remained significant in the subgroup of boys younger than 2 y of age (r(S) = -0.84, n = 11, p = 0.008) who also had greater variance of serum F SH concentrations than 14 control boys of similar age with normally located testes (p < 0.01). hCG stimulation increased serum testosterone and suppre ssed serum FSH concentrations in each boy (n = 9,p < 0.005). In the four ol dest subjects, the serum inhibin B level increased from the mean of 91 to 1 35 pg/mL (p < 0.05), These findings suggest that inhibin B regulates FSH se cretion in early childhood. Moreover, the hCG-induced suppression of FSH se cretion was probably mediated by sex steroids rather than by inhibin B. Fin ally, the increase in serum inhibin B concentration during the hCG treatmen t was likely to be indirect via Leydig cell-Sertoli cell or Sertoli cell-ge rm cell interaction(s).