Characterization of the androgen receptor in the skeletal muscle of the rat.

Skeletal muscle homogenate of prepuberal, adult uncastrated or short-(1-4days) or long-term (20days) castrated male and female rats was incubated at 0degreesC iwth highly labeled (3H)5alpha-dihydrotestosterone (1) or (3H) testosterone. labeled (3H)5alpha-dihydrotestosterone (1) or 3H) testosterone. After incubation bound and free hormone in the 100,000 g cytosol were separated by agargel electrophoresis at low temperature. Furthermore, the percentage distribution of the main metabolites found in the cytosol was analyzed by thin-layer chromatography. Two androgen binding proteins could be found: One with high affinity (apparent dissociation and constant (Kd)= 1.4 - 6.4X10(-9)M) low capacity (receptor), the other with relative low affinity high capacity. The physico-chemical characteristics of the androgen receptor in the rat skeletal muscle cytosol are similar if not identical to those which have been described for the androgen receptor in the prostate and other androgen dependent organs. However, the amount of available 5alpha-DHT-binding sites in the skeletal muscle is about 60 times and 7 times lower than in the prostate and bulbocavernosus/levator ani muscle, respectively. No essential androgen metabolism occurs in vitro at 0degreesC in the skeletal muscle.