Testosterone synthesis in rhesus fetal testes: Comparison between middle and late gestation

Several aspects of testosterone synthesis were examined in fetal testes of rhesus monkeys at middle (Days 79 to 82) and late gestation (Days 140 to 149). Histological examination of fetal testes revealed that Leydig cells are smaller at late gestation and that there are approximately one-third as many Leydig cells per unit area compared with midgestation. The concentration of testosterone in umbilical arterial serum, however, was not significantly lower at late gestation. In vitro synthesis of testosterone and cycle AMP (cAMP) was stimulated by human chorionic gonadotropin (hCG) in tissues collected at both stages of gestation. The testosterone concentration of testicular tissue and testosterone synthesis in the absence of hCG were ~2-fold greater at mid-gestation (P<0.05), but the rate of testosterone synthesis in the presence of hCG did not differ between the two stages. In contrast, cAMP synthesis was 4-fold greater in the absence of hCG and 9-fold greater in the presence of hCG in tissues collected at midgestation (P<0.01). Concentrations of biologically active luteinizing hormone (LH) in the fetal circulation were found to be 2-fold greater at late gestation than at midgestation (P<0.01).