ALPHA-GLUCOCORTICOID AND BETA-GLUCOCORTICOID RECEPTOR MESSENGER-RNA EXPRESSION IN SKELETAL-MUSCLE

The aim of the present study was to investigate the occurrence and aut oregulation of both glucocorticoid receptor mRNAs in rat gastrocnemius muscle. The expression of both receptor forms was studied 1, 4 or 12 hours after intra-tracheal instillation of a high dose (100 mu g) of b udesonide; muscular expression was compared with glucocorticoid recept or expression in lung tissue. After Northern blot analysis, hybridizat ion was performed with glucocorticoid receptor, glyceraldehyde-3-phosp hate dehydrogenase and glutamine synthetase probes. In the gastrocnemi us muscle, both the alpha and beta glucocorticoid receptor mRNA forms were detected and found to be downregulated four hours after the budes onide instillation, alpha/beta glucocorticoid receptor ratios were low er in the gastrocnemius (1.1 +/- 0.2) than in the lungs (2.6 +/- 0.6). In the lungs, at all time points, the average alpha glucocorticoid re ceptor mRNA levels did not differ from controls, although glutamine sy nthetase mRNA levels were upregulated. The beta glucocorticoid recepto r mRNA was slightly reduced at 1 and 4 hours. In conclusion, after int ra-tracheal instillation of budesonide, both alpha and beta glucocorti coid receptor forms were downregulated in muscle tissue. The differenc e in alpha/beta glucocorticoid receptor mRNA ratios and concentrations between lung and gastrocnemius muscle supports the hypothesis of diff erential gene regulation by glucocorticoids in different cell types. ( C) Kluwer Academic Publishers.