Reduced Inhibin and Elevated Gonadotropin Levels in Early Pubertal Boys with Testicular Defects

Abstract

In the prepubertal quiescent period, the control of gonadotropin secretion is assumed to be mediated by neuroendocrine inhibitory mechanisms, whereas little or no effect is thought to be mediated by the gonad. However, in pubertal-aged children with primary gonadal failure, gonadotropins increase to supranormal levels, suggesting that gonadal factors become more important in the control of gonadotropin secretion at that age. These gonadal factors have been poorly characterized so far. To clarify the relationship of inhibin and testosterone to the control of gonadotropin secretion during sexual maturation, we examined serum inhibin, testosterone, LH, and FSH concentrations in 10 boys with testicular defects and in nine healthy boys, in prepuberty and in early puberty. Serum was obtained at 15-min intervals for at least 6 h during the night. Prepubertal-aged boys with testicular defects had only slightly higher FSH levels than healthy boys, and their LH and inhibin levels were no different. In contrast, pubertal-aged boys with testicular defects had higher LH and FSH levels and lower inhibin levels than healthy boys. In prepubertal-aged boys, no correlation was found between individual mean inhibin level and mean FSH or LH level. In contrast, in pubertal-aged boys, an inverse nonlinear relationship between mean inhibin level and mean FSH and LH level was seen. The inverse value for inhibin correlated with FSH (r = 0.74, p < 0.01) and with LH (r = 0.81, p < 0.01). In conclusion, our results suggest that inhibin is a factor involved in the control of gonadotropin secretion in boys, at least in the pubertal period.