Age-related secretion of androstenedione, testosterone and dihydrotestosterone by the human testis.

To study the production of testosterone, dihydrotestosterone (DHT), and androstenedione by the human testis during advancing age, these substances were measured in the spermatic venous blood plasma of 38 17-80 year old men. Samples of blood from the spermatic veins were collected during the operative repair of inguinal hernias. Plasma concentrations were determined by radioimmunoassay after paper chromatography. Control experiments were done with added known amounts of these substances to steroid free plasma. It was found that in old age the testicular production of DHT decreases significantly as well as its concentration in peripheral venous plasma. Spermatic androstenedione is unchanged while testosterone is decreased in senesence. This finding suggests that the decreased Leydig cell function in old age may be partly due to an enzymatic defect in the testicular steroidogenesis pathway because androstenedione is a direct precursor of testosterone.