Testicular reserve of testosterone precursors in primary testicular failure

To explore the abnormal steroidogenesis in subjects with primary testicular failure, we measured serum levels of testosterone (T) and its precursors androstenedione (delta 4A) and 17-hydroxyprogesterone (17-OHP) in the basal state and after stimulation by human chorionic gonadotropin (hCG) for 4 hours (acute reserve) or 72 hours (chronic reserve). Subjects with primary testicular failure had decreased mean basal serum T, decreased mean chronic T reserve, and absent mean acute T reserve. In contrast, these subjects had normal mean basal serum 17-OHP and delta 4A, normal chronic 17-OHP reserve, and non-zero mean acute 17-OHP and delta 4A reserve, although mean chronic delta 4A reserve was reduced. Heterogeneity of biochemical abnormalities depending on the etiology of testicular failure was apparent. In primary testicular failure, the testicular reserves of the T precursors 17-OHP and delta 4A are better maintained than is the reserve of T itself, raising the possibility that this disorder might be associated with biochemical blocks in conversion of T precursors to T.