Human testicular LH receptors: correlations with circulating gonadotrophins and testicular steroid secretion

Testicular androgen production is regulated by circulating LH, the effect of which is mediated by its testicular membrane receptors. In the present study, testicular [125I]hCG binding in man was investigated and found to be characterized by saturability and high affinity (mean KD in testes of 21 patients with prostatic carcinoma = 1.64 X 10(-10) M), and stimulated testosterone production in dispersed interstitial cells in vitro. The concentrations of the LH receptors correlated with serum FSH concentrations (r = 0.52, P less than 0.05) but not with circulating LH levels. Neither had they any correlation with intratesticular testosterone, 5 alpha-dihydrotestosterone, androstenedione, progesterone, 17-hydroxyprogesterone or pregnenolone concentrations, which may be due to the fact that LH receptors are confined to Leydig cells, whereas steroids may be unevenly distributed in the different cells of the testis. In contrast, the concentrations of the LH receptor displayed positive correlations with the concentrations of testosterone (r = 0.81, P less than 0.001), androstenedione (r = 0.54, P less than 0.05), 17-hydroxyprogesterone (r = 0.76, P less than 0.001) and progesterone (r = 0.60, P less than 0.05) in the spermatic vein serum of the patients. Our data suggest that the Leydig cells mainly responsible for steroid secretion into the blood are under gonadotrophic control exerted via their receptors, whereas Leydig cell function is not rapidly reflected in steroid concentrations within the testis itself.