The Aging Leydig Cell: III. Gonadotropin Stimulation in Men

To assess the capacity of aging human Leydig cells to respond to intramuscular injection of hCG, six healthy men, 68 to 86 years old, and eight healthy younger subjects, 25 to 42 years old, were studied. After two control specimens, each subject was given hCG (40 IU/kg of body weight intramuscularly) at 0900 hours. Blood specimens were then obtained hourly for 6 hours and at 24, 48, and 72 hours. The younger men had higher control concentrations of testosterone ( P < 0.05). Both groups demonstrated biphasic elevations of circulating testosterone and 170H‐progesterone with a nadir at 5 hours and 6 hours separating the rises. The early (1–6 hours) and late (24, 48, and 72 hours) testosterone and 170H‐progesterone responses to hCG were significantly lower in older men. The older men demonstrated significant estradiol increases at 3, 4, and 6 hours, while the younger group had a significant 2‐hour rise. However, the peak (24‐hour) estradiol rises were significantly greater in the younger men. We conclude that theb aged Leydig cell demonstrates altered early (1–6 hours) and late(24, 48, and 72 hours) responses to intramuscular injection of hCG, as assessed by circulating concentrations of testosterone, 17OH‐progesterone, and estradiol.