Inverse relationship between serum inhibin B and FSH levels in prepubertal boys with cryptorchidism.

To investigate the gonadal control of FSH secretion in prepuberty, we studied the relationship between circulating inhibin B and FSH levels in 16 prepubertal boys with cryptorchidism (age range, 1-8 y). The effect of Leydig cell stimulation on the secretion of inhibin B, sex steroids, and FSH was investigated in nine boys who were given human chorionic gonadotropin (hCG) treatment. In these boys, serum inhibin B, testosterone, estradiol, and gonadotropin levels were measured before and on the fourth day of the last (third) hCG injection, given at 1-wk intervals. Except for one boy with both high inhibin B and FSH concentrations, basal serum levels of these hormones correlated negatively (r(s) = -0.79, n = 15, p < 0.005). This inverse relationship 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 FSH concentrations than 14 control boys of similar age with normally located testes (p < 0.01). hCG stimulation increased serum testosterone and suppressed serum FSH concentrations in each boy (n = 9, p < 0.005). In the four oldest subjects, the serum inhibin B level increased from the mean of 91 to 135 pg/mL (p < 0.05). These findings suggest that inhibin B regulates FSH secretion in early childhood. Moreover, the hCG-induced suppression of FSH secretion was probably mediated by sex steroids rather than by inhibin B. Finally, the increase in serum inhibin B concentration during the hCG treatment was likely to be indirect via Leydig cell-Sertoli cell or Sertoli cell-germ cell interaction(s).