Mineralocorticoid binding in cultured smooth muscle cells and fibroblasts from rat aorta

Based on changes in electrolyte content, the direct action of adrenal steroids on blood vessel wall has been postulated for many years. High affinity corticosteroid binding sites have been found in both smooth muscle and fibroblast cultures from aortic explants of Sprague-Dawley rats. [³H]-aldosterone and [³H]-corticosterone bind to the same two distinct classes of sites: (a) corticoid receptor I with a K_d ranging from 0.11 to 1.31 × 10^-9 M and a B_max ranging from 22 to 282 mol × 10^-18/μg DNA (measured by either steroid); (b) corticoid receptor II with a K_d ranging from 2.09 to 20.83 × 10^-9 M and a Binmax ranging from 97 to 1410 mol × 10^-18/μg DNA (measured by [³H]-aldostcronc) or a B_max ranging from 1336 to 5520 mol × 10^-18/μg DNA (measured by [³H]-corticosterone or [³H]-dexamethasone). Corticoid receptor I is easily detected by [³H]-aldostcrone in the presence of 40 nM dexamethasone and is not detected by [³H]-dexamethasone alone. Displacement experiments with corticoid receptor I labeled with [³H]-aldoslerone indicate the following hierarchy of binding: corticosterone ≥ desoxycorticosterone ≥ aldosterone > cortisol ≥ dexamethasone > 17β-estradiol = 5α-dihydrotestosterone. Displacement experiments with corticoid receptor II labeled with [³H]-dexamethasone indicate the following binding hierarchy: corticosterone = desoxycorticosterone = cortisol = dexamethasone > aldosterone > 17β-estradiol = 5α-dihydrotestosterone. The steroid specificity of corticoid receptor I is unique and distinguishes these sites from classical mineralocorticoid or glucocorticoid receptors. These sites may mediate new physiological effects of corticosterone, desoxycorticosterone and/or aldosterone in vascular tissue.