Simultaneous measurements of testosterone and three 5 alpha-reduced androgens in the venous effluent of immature rat testes in situ.

Simultaneous measurements were made by radioimmunoassay of testosterone, 17 beta-hydroxy-5 alpha-androstan-3-one (DHT), 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol), and 5 alpha-androstane-3 beta, 17 beta-diol (3 beta-diol) in the testicular venous plasma (TVP) and peripheral plasma (PP) of 30, 45, and 55 day old rats. At 30 days of age, the preponderant androgen in both plasmas was 3 alpha-diol but testosterone predominated by day 55. Testosterone levels increased with age in both TVP (6.39, 15.08, and 54.93 ng/ml on days 30, 45, and 55 respectively) and PP (0.13, 0.56, and 1.02 ng/ml on days 30, 45 and 55 respectively) whereas 3 alpha-diol concentrations decreased in TVP (48.07 ng/ml, day 30; 24.85 ng/ml, day 55) though not peripherally (range: 0.41-0.52 ng/ml). DHT was low in both TVP and PP and appeared to rise only slightly although the increase was not statistically significant. Levels of 3 beta-diol remained low and unchanged. These observations suggest that the total androgen content of the venous effluent from the prepubertal rat testis is quite high and that significant changes in peripheral interconversions of androgens are occurring during sexual maturation.