Binding of 「3 H」triamcinolone to cytosolic fractions of rat brain

Binding of 「^^3 H」triamcinolone acetonide (TA) was detected in cytosol but not in membrane fractions of rat brain. The binding increased with incubation time up to 5 hr and reached a plateau within 16 hr after the initiation of incubation at 2℃, while elevation of incubation temperature to 30℃ markedly reduced binding at equilibrium due to rapid dissociation of bound 「^^3 H」TA. Among a variety of steroids tested, TA was the most potent displacer of the binding at equilibrium at 2℃, followed by dexamethasone, deoxycorticosterone, progesterone, prednisolone and hydrocotisone in a rank order of decreasing potency. Pharmacological screening on 120 miscellaneous compounds revealed that Zn^2+ potently inhibited the binding in a concentration-dependent manner at concentrations above 1 μM . These results support the proposal that Zn^2+ may play some unidentified role in signal transduction processes mediated by glucocorticoid receptors in cytosolic fractions of rat brain.