Demonstration of specific glucocorticoid binding sites in bovine cornea

Specific [3H]-dexamethasone binding sites were demonstrated in bovine corneal cytosol using titration analyses. Specific glucocorticoid binding to corneal cytosol exhibited a single class of sites with apparent dissociation constants of 4-6 nM and 68-72 fmol binding sites mg-1 cytosolic protein. Association of steroid with these binding sites was temperature- and time-dependent. Specific binding was maximal at 4 degrees C after 6 hr and was somewhat lower at 25 degrees C and lowest at 37 degrees C. Presence of increasing amounts of certain unlabeled steroids with glucocorticoid activity inhibited [3H]-dexamethasone binding in a dose-dependent manner. The order, beginning with the most potent inhibitor of binding, was triamcinolone acetonide greater than fluorometholone greater than dexamethasone greater than medroxy progesterone acetate greater than 11 beta-OH-progesterone greater than prednisolone acetate greater than prednisolone greater than cortisol greater than corticosterone . Other steroids exhibiting less inhibition of [3H]-dexamethasone binding were cortexolone greater than prednisone greater than dexamethasone phosphate greater than progesterone greater than prednisolone phosphate greater than cortisone greater than 17 alpha-OH progesterone greater than estradiol-17 beta greater than testosterone greater than 11 alpha,17 alpha,21-OH-progesterone. These data suggest that the influence of glucocorticoids and drugs with this type of normal activity on corneal cells is mediated by an intracellular receptor protein.