Chick oviduct glucocorticosteroid receptor

Open Access
Publisher Website
Google Scholar
Abstract
The glucocorticosteroid receptor (GR) has been studied in oviduct cytosol prepared from estrogen‐primed, 4‐week‐withdrawn chicken. The equilibrium dissociation constant was 6 nM for dexamethasone, and 18300 receptor sites/cell were measured assuming that all cells contain identical concentrations of GR. Dexamethasone, used in most studies investigating glucocorticosteroid action, was found not to be the best GR ligand. The affinities of several natural and synthetic glucocorticosteroids for GR increased in the following order: cortisol < deoxycorticosterone < dexamethasone < corticosterone < triamcinolone acetonide. The synthetic steroid RU 486 was the most specific ligand of GR (its affinity was ∼ 10‐fold higher than that of triamcinolone acetonide), while it did not bind either to plasma transcortin (which binds dexamethasone nor, surprisingly, to progesterone receptor (PR), contrary to what occurs in mammalian species.The molybdate‐stabilized, 8‐S form of GR was prepared from withdrawn chick oviduct, whole chick embryo or cultured chick embryo fibroblasts (which do not contain PR), and was labeled with either [3H]dexamethasone or [3H]RU 486. The sedimentation coefficient of radioactive ligand–8‐S GR complexes was shifted towards heavier forms after incubation with polyclonal (IgG‐G3) or monoclonal (BF4) antibodies generated against the molybdate‐stabilized, 8‐S form of the chick oviduct PR. Since neither IgG‐G3 nor BF4 interacted with the steroid binding 4‐S form of GR, it is suggested that these antibodies recognized a non‐steroid binding protein common to molybdate‐stabilized, 8‐S forms of GR and PR.