Formation and Metabolism of Testosterone in Testicular Tissue of Immature Rats

Abstract

Testicular tissue from newborn, 20- and 90-day-old rats was incubated with radiolabeled testosterone or androstenedione. Tissue from newborn and adult rats actively metabolized androstenedione (75–80 % conversion), with testosterone being the major product. Testosterone, on the other hand, was poorly metabolized, only 10–20 % being converted to androstenedione. In incubates of testicular tissue from 20-day-old rats, both testosterone and androstenedione were converted primarily (70–80%) to 5α-reduced androgens. The addition of heparin almost completely blocked formation of 5α-reduced androgens from testosterone in incubates of testicular tissue from 20-day-old rats, indicating inhibition of testicular 5α-reductase by heparin. Incubation of androstenedione in a similar system resulted in accumulation of testosterone and only minor formation of 5α-reduced androgens, suggesting that the 5α-reduced androgens formed in incubates of testicular tissue in the absence of heparin are, most likely, products of testosterone reduction. In experiments where testicular tissue from 20-day-old rats was incubated with progesterone in the presence of heparin, testosterone was the major metabolic product, confirming the finding that heparin is an inhibitor of testicular 5 areductase, and demonstrating the specificity of its inhibitory action. On the basis of these observations it is concluded that, in incubates of immature testes with progesterone or androstenedione, testosterone is formed but is rapidly reduced to a series of 5α-reduced androgens. (Endocrinology89: 679, 1971)