title: Depletion of [3H]methyltrienolone cytosol binding in glucocorticoid-induced muscle atrophy.
abstract: The present study was undertaken to determine cytosol binding properties of [3H]methyltrienolone, a synthetic androgen, in comparison with [3H]dexamethasone, a synthetic glucocorticoid, under conditions of glucocorticoid excess in skeletal muscle. Male hypophysectomized rats received either seven daily subcutaneous injections of cortisone acetate (CA) (100 mg X kg-1 body wt) or the vehicle, 1% carboxymethyl cellulose. Following treatment, both [3H]dexamethasone and [3H]methyltrienolone-receptor concentrations were decreased from those in vehicle-treated rats by more than 90 and 80%, respectively, in CA-treated animals. Scatchard analysis of [3H]methyltrienolone binding in muscles of vehicle-treated animals became nonlinear at high concentrations of labeled ligand and were reanalyzed by a two-component binding model. The lower affinity, higher capacity component, which was attributed to binding of methyltrienolone to a "dexamethasone" component, disappeared in muscles of CA-treated rats and Scatchard plots were linear. Receptor concentrations of the higher affinity lower capacity "methyltrienolone" component were similar in muscles of vehicle-treated and CA-treated groups. From competition studies, the high relative specificities of glucocorticoids for [3H]methyltrienolone binding in muscles of vehicle-treated animals were markedly reduced by CA treatment. In addition, the binding specificity data also showed strong competition by progesterone and methyltrienolone for [3H]dexamethasone binding and estradiol-17 beta for [3H]methyltrienolone binding. These results demonstrate that most of the [3H]methyltrienolone binding is eliminated under in vivo conditions of glucocorticoid excess. Furthermore, the competitiveness of various steroids for receptor binding suggests that rat muscle may not contain classic (ligand-specific) glucocorticoid and androgen receptors.
mesh_terms: D000728:Androgens / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D003348:Cortisone / Q000031:analogs & derivatives / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D003907:Dexamethasone / Q000378:metabolism; D004963:Estrenes / Q000378:metabolism*; D005938:Glucocorticoids / Q000378:metabolism / Q000494:pharmacology*; D007016:Hypophysectomy; D008297:Male; D015741:Metribolone; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D009133:Muscular Atrophy / Q000139:chemically induced* / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000187:drug effects / Q000378:metabolism
chemical_list: D000728:Androgens; D004963:Estrenes; D005938:Glucocorticoids; D011965:Receptors, Glucocorticoid; D015741:Metribolone; D011374:Progesterone; D003907:Dexamethasone; D003348:Cortisone