[The metabolism of delta4-3-oxosteroids in rat liver].

The enzymatic reactions are described by which delta4-3-oxosteroids, specially testosterone, are inactivated in rat liver. The delta4-3-oxosteroid-5 alpha-reductase in liver microsomes was studied intensively and it was found that it is an enzyme system. The 5 alpha-reduction of testosterone with NADPH or with NADH depends upon different enzymes or enzyme systems.