Effect of castration on the metabolism of androgens in rat skeletal muscle

1. 1. The metabolic conversion of testosterone and 17β-hydroxy-5α-andro-stan-3-one by cell fractions from skeletal muscle was examined. 2. 2. Little or no conversion of testosterone to 17β-hydroxy-5α-androstan-3-one is observed with any skeletal muscle fraction studied. 3. 3. The cytosol from all muscles examined contained substantial levels of the enzyme 3α-hydroxysteroid oxidoreductase, which converts 17β-hydroxy-5α-androstan-3-one to 5α-androstane-3,17β-diol. 4. 4. The K_m of the reaction in the three muscles (extensor digitorum longus, soleus and levator ani) is in the order of 3-6 × 10^-6 M. 5. 5. Following castration, there is no significant change in the K_m value of this reaction in any of the muscles. 6. 6. The V_max of the conversion in the extensor digitorum longus and soleus are similar (in the order of 2.0 × 10^-11 mol/mg per min) and castration has no significant effect on V_max in either of these muscles. 7. 7. V_max is significantly lower for the levator ani (3.4 × 10^-12 mol/mg per min) than for the extensor digitorum longus and soleus. 8. 8. Following castration the V_max for the levator ani undergoes a significant rise which peaks at 3 days.