Steroid delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase in the rat epididymis during development

delta 4-5 alpha-Reductase activity is apparently regulated by a testicular factor(s) secreted directly into the epididymis, whereas 3 alpha-hydroxysteroid dehydrogenase activity, in this tissue, appears to reflect circulating androgen levels. To test whether the factor(s) regulating delta 4-5 alpha-reductase activity is directly associated with spermatozoa, a developmental study was undertaken to temporally correlate various parameters of the male reproductive tract with enzymatic activities. delta 4-5 alpha-Reductase activity is first detectable at 21 days of age. Activity increases until day 77, after which time enzymatic activity decreases by more than 60%, reaching steady adult values at 105 days. 3 alpha-Hydroxysteroid dehydrogenase activity is detectable as early as 7 days. Levels of this enzyme increase until day 63, after which time constant adult values are maintained until at least 1 yr. Spermatids and/or spermatozoa are first seen in the testes at 42 days, and plateau levels are reached by day 77. Spermatozoa are first seen in the epididymis at 49 days and reach maximal values by 91 days; no significant change occurs thereafter (until 365 days). Increases in seminal vesicle and ventral prostate weights are of a sigmoidal type, paralleling increases in plasma androgens, with the greatest rate of rise between days 35--63. This sigmoidal type of increase in tissue weights and plasma androgens is similar to that seen for epididymal 3 alpha-hydroxysteroid dehydrogenase but markedly different from that found for delta 4-5 alpha-reductase. The importance of delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase activities in the epididymis before the entry of spermatozoa and the decline in delta 4-5 alpha-reductase activity with age is discussed.