| Abstract: | A mechanism which determines the difference in the ability of deoxycorticosterone (DOC) to inhibit the binding of 3H-triamcinolone acetonide (3H-TA) to glucocorticoid receptors of rat heart and liver cytosols was investigated. DOC was found to strongly inhibit the binding of 3H-TA by heart cytosol, but to exert only a slight inhibitory effect towards the live cytosol binding. This difference was not due to the influence of the enzymes sensitive to molybdate ions, the presence of DOC-degrading enzymes or contamination of liver cytosol by blood serum. The liver cytosol devoid of the glucocorticoid receptor activity by heating was found to contain a factor modifying the "in vitro" interaction of DOC with the heart cytosol glucocorticoid receptors (receptor modifying factor, RMF). This factor is coeluted with the high molecular weight fraction during gel filtration, is precipitated at 50-70% ammonium sulphate saturation, can be absorbed by DEAE-Sephacel from cytosol at pH 7.4 under hypotonic conditions and extracted at about 0.06 M KC1. The sensitivity to proteases and the lack of sensitivity to nucleases point to the proteinic nature of the factor. It was assumed that in terms of the interaction of some steroids with glucocorticoid receptors, the tissue specificity can, at least partly, be explained by the differences in RMF concentration. |
