Binding and metabolism of testosterone and of 5α-dihydrotestosterone in bulbocavernosus/levator ani (BCLA) of male rats: Invivo and invitro studies

Abstract

1. 1.The binding of labelled compounds after the i.v. administration of tritiated testosterone or of 5α-dihydrotestosterone (5α-DHT) has been demonstrated by agargel electrophoresis at low temperature in the 100,000 g cytosol of the rat bulbocavernosus/levator ani muscle complex (BCLA). No binding was found in skeletal muscle (SM). This compared well to a significantly higher uptake of radioactivity by the 100,000 g cytosol of the rat bulbocavernosus/levator ani muscle complex (BCLA). No binding was BCLA and SM testosterone itself was the predominant compound (73–77%), the amounts of 5α-DHT (5–7%) being negligible, while in prostate (PR) and seminal vesicles (SV) more than 65% of the testosterone had been converted to 5α-DHT. 2. 2. By in vitro studies the characterization of the BCLA cytosol receptor was accomplished as follows: (a) in bulbocavernosus (BC) and levator ani (LA) an identical androgen receptor was found; (b) the receptor showed a higher affinity to 5α-DHT than to testosterone; (c) a plasma contamination was excluded; (d) an inhibition of the specific binding of 5α-DHT and of testosterone was demonstrated by the respective unlabelled compounds and by cyproterone acetate; (e) no displacement was observed with cortisol; (f) under identical conditions no binding occurred in the SM. 3. 3. Binding, uptake and metabolism of testosterone and of 5α-DHT have been compared between PR, SV, BCLA and SM. From the results obtained one may conclude that the androgenic endpoint PR differs from the myotrophic endpoint SM by higher 5α-reductase activities and by larger amounts of specific androgen receptors. Physico-chemical differences between the various receptor proteins could not be found.