Classification of anabolic steroids using the method of competitive metabolism.

The effect of increasing concentrations of testosterone (T) and 19-nortestosterone (N) on the in vitro metabolism of [3H]N in minced tissue of the rat seminal vesicle indicates that T and N are equally appropriate substrates for the 5 alpha-reductase. Experiments in which increasing concentrations of 17-methyl-T (MT) or 1-ene-MT were incubated with [3H]T and vesicular mince have revealed that the formation of [3H]5 alpha-dihydro-T is suppressed markedly by MT while 1-ene-MT has no measurable effect. Since 5 alpha-dihydro-MT binds to the androgen receptor with a higher affinity than MT does and (relative to T) MT does not exhibit myotropic-androgenic (= M-A) dissociation, it can be concluded that MT is, whereas 1-ene-MT is not a substrate for the 5 alpha-reductase. Our present and previous data suggest that N exemplifies one class of anabolic steroids that become less androgenic due to 5 alpha-reduction, it shows high myotropic activity, M-A dissociation (= 7-30) and affinity to the androgen receptor. On the other hand, 1-ene-MT belongs to another class of anabolic steroids that are not substrates for the 5 alpha-reductase, exhibit a relatively small myotropic activity, M-A dissociation (= 2-3) and receptor affinity.