GLUCOCORTICOID RECEPTORS IN THE PIG INTESTINAL-TRACT AND MUSCLE-TISSUE

Due to the known differences of protein turnover in skeletal muscle (s low turnover) and intestinal tract (rapid turnover), these tissues wer e analysed for the free glucocorticoid receptor (GR) concentrations. C ytosol was prepared from different parts of pig intestinal tract and t wo different muscles (longissimus thoracis: ML; trapezius: MT) under e ither energy restriction (5.8 MJ ME; 4 kd/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 Loth for muscle and gut tissue and the KD (0.4 +/- 0.04 nM; 0.7 +/- 0.02 nM) as well as B-max (0.2 +/- 0.01 nM; 1.2 +/- 0.02 nM) p ointed to specific binding. GR were generally high in intestinal tract irrespective of the anatomical site, but were significantly (P less t han or equal to 0.001) higher under energy restriction compared to ade quate feeding (103.2 vs. 76.5 fmol/mg protein). GR was much lower in m uscle tissues and tended to be slightly higher in MT (with high propor tion of red fibres) compared to ML (white fibres) (12.4 vs. 9.1 fmol/m g 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.