A profile of the intestinal mucosal corticosteroid receptors in the domestic duck.

The corticosteroid receptor profile of the intestinal tract of the domestic duck (maintained on either a low-sodium (LS) or a high-sodium (HS) diet) was investigated. Using tritiated triamcinolone acetonide (TA), corticosterone, or aldosterone as ligands, cytoplasmic mineralocorticoid receptors (MR, type I) and glucocorticoid receptors (GR, type II) were found in the mucosal cytosol of the jejunum and colon with the following binding parameters: LS jejunum GR-Kd, 3.4 nM; Nmax, 245 fmol/mg protein; MR-Kd, 0.54 nM; Nmax, 35 fmol/ mg protein; colon GR-3.2 nM; Nmax, 531 fmol/mg protein; MR-Kd, 0.55 nM; Nmax, 113 fmol/mg protein; HS jejunum GR--Kd, 3.2 nM; Nmax, 531 fmol/mg protein; MR--Kd, 0.30 nM; Nmax, 50 fmol/mg protein; colon GR--Kd, 1.1 nM; Nmax, 572 fmol/mg protein; MR--Kd, 0.68 nM; Nmax, 221 fmol/mg protein. The diet little influenced the GR binding parameters, while the MR (aldosterone) binding parameters showed a down-regulation following LS (high circulating aldosterone) diets. The competition hierarchy of radioinert steroids on the formation of the [3H]corticosterone-receptor complex was corticosterone = cortisol = 11-deoxycorticosterone greater than aldosterone = TA = dexamethasone much greater than 11-deoxycortisol; with [3H]aldosterone, the competition was corticosterone = progesterone = 11-deoxycorticosterone greater than aldosterone = cortisol = TA = dexamethasone greater than 11-deoxycortisol greater than 11-dehydrocorticosterone. The intestinal mucosal receptor was deactivated following treatment with trypsin. On linear sucrose gradients, receptor-ligand complexes sedimented with a single peak at 8.5 S (hypotonic gradient) and 4.0-4.5 S (hypertonic gradient), respectively. Heat-activated [3H]TA- and [3H]aldosterone-receptor complexes bound avidly to DNA-cellulose and, upon ion-exchange chromatography on DEAE-Sephacel, the presence of the negatively charged unactivated and the more positively charged activated complexes could be shown. The hydrodynamic parameters, determined by gel-filtration chromatography, gave for all three ligand-receptor complexes molecular weight values from 334,000 to 351,000 and Stokes radii from 76.8 to 80.0 A. From these studies it was concluded that the duck intestinal tract possesses vertebrate-type GR and MR, though these receptors were much less specific than their mammalian counterparts. The duck intestinal corticosteroid receptor was found to be different from those of the teleost fish and anuran amphibian, establishing the possibility of a biochemical evolution in nonmammalian intestinal corticosteroid receptor conformation.