Prediction of testosterone response to human chorionic gonadotrophin in idiopathic hypogonadotropic hypogonadism patients.

In clinical practice, the human chorionic gonadotrophin (hCG) stimulation test is widely used to evaluate testicular function. Inhibin B, a gonadal peptide regulating follice-stimulating hormone (FSH) secretion, is an established marker of Sertoli cell function and spermatogenesis in adults. The aim of this study was to determine whether basal inhibin B levels are able to predict testosterone response to hCG in idiopathic hypogonadotropic hypogonadism (IHH) patients and to evaluate the correlation between inhibin B and gonadotropins in these patients and controls. Inhibin B (n=15) and other hormones (n=29) were measured in 29 patients with IHH and 32 controls. Inhibin B (n=8) and testosterone levels (n=25) before and after hCG stimulation were measured in 25 male patients with IHH by an immunoassay specific for inhibin B. Basal inhibin B was compared to the testosterone increase after hCG. There was a significant increase in inhibin B (22.6 +/- 9.8 vs 45.07 +/- 13 pg/mL; p=.005), free testosterone (2.92 +/- 0.55 vs. 7.9 +/- 1.5 pg/mL; p=.002), and total testosterone (69.0 +/- 15.9 vs. 184.9 +/- 44.1 ng/mL; p = .013) levels 72 hours after hCG injection. Inhibin B and the hCG-induced free testosterone and total testosterone increment correlated strongly (r=0.802, P<.001; r=0.793, P<.001, respectively). We conclude that basal inhibin B predicts the testosterone response to hCG in IHH patients and therefore gives reliable information about Leydig cell reserve. Furthermore, inhibin B levels show negative correlation with luteinizing hormone (LH) in control patients and positive correlation with FSH and LH in IHH patients. LH may effect inhibin B secretion. Further studies are necessary to define the physiology of inhibin B in human males.