The presence of corticosteroid receptor activity in the gills of the brook trout, Salvelinus fontinalis.

Gill tissue from brook trout was examined for the presence of cortisol receptors. Both cytosolic and nuclear preparations from the gills manifested high equilibrium association constants (Ka) and low maximum binding capacities (Nmax) indicative of high-affinity and low-capacity receptor activity (cytosol: Ka = 0.31 +/- 0.02 X 10(9)/M, Nmax = 223.9 +/- 22.8 fmol/mg protein; nuclear extract: Ka = 0.02 +/- 0.003 X 10(9)/M, Nmax = 424.6 +/- 96.3 fmol/mg protein). Gel permeation (Sephacryl S-300) column chromatography gave two incompletely separated peaks at 326,000 and 189,000 Da and Stokes radii of 5.96 and 4.81 nm using [3H]triamcinolone acetonide and only one peak at 219,000 Da and 5.4 nm using [3H]cortisol. The binding of the synthetic compounds, triamcinolone acetonide and dexamethasone, appears to be different from that of the natural steroid, cortisol. The receptor activity appears to be highly specific for cortisol since cortisone and 11 beta,17 alpha,21-trihydroxy-4-pregnen-3,20-dione-21-phosphate bind with much lower affinity. The gill tissue cytosol fractions had the highest cortisol-binding activity, followed by liver, intestine, and muscle. The association constants for the liver, intestine, and muscle were the same order of magnitude as that for the gill. These results are consistent with the concept of nonmembrane steroid receptors of target organs.