Specific glucocorticoid receptor in the iris--ciliary body of the rabbit.

The cytoplasm of the iris--ciliary body of the rabbit contains a receptor capable of specifically binding dexamethasone. This binding protein has a high affinity for dexamethasone (average KD = 2.0 X 10(-8) M), a low capacity (average 4.8 X 10(-13) mol of steroid bound per milligram of protein), and extreme heat sensitivity; it exhibits a pattern of competition virtually identical to that obtained with glucocorticoid receptors from other tissues and shows characteristic physicochemical behavior in various salt concentrations. The demonstration of a specific dexamethasone receptor in the iris--ciliary body provides the first direct biochemical evidence that these tissues may function as a target organ for glucocorticoids.