Studies on the kinetics of the interaction of 7 alpha-hydroxytestosterone with the steroid 5 alpha-reductase

Microsomal preparations from adult male rat testicular interstitial cells were incubated with tritiated testosterone. Added 7 alpha-hydroxytestosterone, (7 alpha,17 beta-dihydroxy-4-androsten-3-one), at levels which appear to exist in the adult testis, inhibited production of labelled 5 alpha-reduced steroids in a graded fashion. This interaction is not competitive and occurs only at high substrate levels, such as those found in steroid-producing organs. Relationships to pubertal changes in steroid metabolism are discussed.