Glucocorticoid receptors in the pig intestinal tract and muscle tissue

Due to the known differences of protein turnover in skeletal muscle (slow turnover) and intestinal tract (rapid turnover), these tissues were analysed for the free glucocorticoid receptor (GR) concentrations. Cytosol was prepared from different parts of pig intestinal tract and two different muscles (longissimus thoracis: ML; trapezius: MT) under either energy restriction (5.8 MJ ME; 4 kg/d) or sufficient supply (14.0 MJ ME; 4 kg/d) for 4 days before sacrification. Care was taken that all samples were obtained within 15 min post-mortem and that premortem treatment did not elevate circulating cortisol. A Scatchard plot was performed both for muscle and gut tissue and the KD (0.4 +/- 0.04 nM; 0.7 +/- 0.02 nM) as well as Bmax (0.2 +/- 0.01 nM; 1.2 +/- 0.02 nM) pointed to specific binding. GR were generally high in intestinal tract irrespective of the anatomical site, but were significantly (P < or = 0.001) higher under energy restriction compared to adequate feeding (103.2 vs. 76.5 fmol/mg protein). GR was much lower in muscle tissues and tended to be slightly higher in MT (with high proportion of red fibres) compared to ML (white fibres) (12.4 vs. 9.1 fmol/mg protein). GR in muscles was not significantly influenced by energy. The tissue specific differences in GR provide the explanation for the known differences in the protein turnover rate.