Is the 5 alpha-reductase-3 alpha-hydroxysteroid dehydrogenase complex associated with the myelin in the peripheral nervous system of young and old male rats?

The formation of the 5 alpha-reduced metabolites of testosterone, 5 alpha-androstan-17 beta-ol-3-one (dihydroxytestosterone, DHT) and 5 alpha-androstan-3 alpha, 17 beta-diol (3 alpha-diol) was evaluated in sciatic nerve fragments and homogenates and in the myelin purified from the sciatic nerve of adult (60-90-day-old) male rats. The effects of aging on the metabolism of testosterone in the sciatic nerve was also evaluated using 20-month-old animals. In the sciatic nerve, tissue homogenization and myelin purification are associated with a marked decrease in the 5 alpha-reductase activity; these data do not appear to be consistent with a possible association of the enzyme with myelin membranes, as it occurs in the CNS. However, the results may be subject to other interpretations which are presented in the discussion. The formation of 3 alpha-diol is higher in sciatic nerve fragments than in homogenates or in the purified myelin. This occurs when testosterone is used as the substrate. In aged animals, the same pattern is observed but at a lower level. In the incubations in which the formation of 3 alpha-diol was evaluated using DHT as the substrate in fragments, homogenates and purified myelin of the sciatic nerve of either adult or old animals, it was found that the yields of this metabolite are higher than those obtained following incubation with testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)