Corticosterone binding sites along the rat nephron.

Glucocorticoids influence numerous kidney functions but the precise location of glucocorticoid receptors in the nephron is not known. To identify the renal binding sites of corticosterone, the natural glucocorticoid in the rat, we measured the binding of [3H]corticosterone to discrete nephron segments microdissected from adrenalectomized rats. Highest specific binding capacity at 25 degrees C (expressed as fmol X cm-1 +/- SE) was found in the cortical collecting tubule (9.69 +/- 0.77) followed in decreasing order by the distal convoluted tubule (2.70 +/- 0.49), medullary collecting tubule (2.58 +/- 0.64), proximal convoluted tubule (1.09 +/- 0.10), and pars recta (0.57 +/- 0.08). Binding was lowest in the thick ascending limb of Henle's loop, with comparable values in the medullary (0.27 +/- 0.05) and cortical (0.26 +/- 0.05) portions of this segment. The apparent maximal binding capacity of the cortical collecting tubule for corticosterone exceeded by nearly two orders of magnitude that of aldosterone previously measured by us in this structure, which is in agreement with the observations of other investigators in kidney cytosol. Specific binding of corticosterone can be demonstrated along the entire rat nephron, but binding sites are concentrated in the cortical collecting tubule. This segment appears to be the main target site for corticosterone as it is for aldosterone.