Abstract
Homogenates of seminiferous tubules isolated from 26-day-old rats were fractionated by ultracentrifugation and the fractions incubated with [ 3H]-testosterone and [ 3H]-dihydrotestosterone to study the subcellular distribution of testosterone oxidoreductases. Total tissue homogenates showed active 5α-reductase and 3α-hydroxysteroid dehydrogenase activities and little 3β-hydroxysteroid dehydrogenase. 3α-Hydroxysteroid dehydrogenase was mainly located in the soluble fraction of the cells while 3β-hydroxysteroid dehydrogenase and 5α-reductase activities were found to be present in the particulate fractions of the cytoplasm and in the nuclei. This distribution of enzyme activities is similar to that reported for other androgen target tissues. The highly active soluble 3α-hydroxysteroid dehydrogenase is probably responsible for the high concentrations of 5α-androstan-3α,17β-diol that we had previously found in the seminiferous tubules at the time of initiation of the meiotic division.
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