ru-28318 and 11-dehydrocorticosterone

The testis is known to be a site of corticosterone action, and testosterone production in Leydig cells is directly inhibited by glucocorticoids. Glucocorticoids bind to both glucocorticoid receptors (GRs) and to mineralocorticoid receptors (MRs). In Leydig cells, selective mineralocorticoid binding could result from oxidative inactivation of glucocorticoid by type 1 and/or 2 11beta-hydroxysteroid dehydrogenase (11betaHSD), as both isoforms are expressed. However, it remains unclear whether Leydig cells express MRs and respond directly to mineralocorticoid action. Therefore, the aims of the present study were to ascertain: (1) whether MR mRNA, protein and receptor binding are present in Leydig cells; and (2) if the mineralocorticoid modulates testosterone production. The mRNA encoding MR, as well as protein, and binding activity were each observed in adult rat Leydig cells. MR-ligand binding specificity within isolated Leydig cells was evaluated further by measuring displacement of MR binding to aldosterone by corticosterone in the presence and absence of carbenoxolone, an inhibitor of 11betaHSD1 and 2 that decreases conversion to biologically inert 11-dehydrocorticosterone. Carbenoxolone inhibited 11betaHSD oxidative activity, and reduced corticosterone-binding by 50%. Mineralocorticoid effects on steroidogenesis were assessed in the presence of aldosterone (0.01-10 nM) with or without the MR antagonist, RU28318. Aldosterone induced dose-dependent increases in both basal and luteinizing hormone-stimulated testosterone production. RU28318 eliminated the increase, indicating that these effects of aldosterone were mediated by the MR. The effects of aldosterone and luteinizing hormone (0.1 ng/ml) on testosterone production were synergistic, suggesting that the two hormones increased steroidogenesis through separate pathways. We conclude that Leydig cells express MRs and that testosterone production is subject to regulation by aldosterone.

Topics: 11-beta-Hydroxysteroid Dehydrogenase Type 1; 11-beta-Hydroxysteroid Dehydrogenase Type 2; Aldosterone; Animals; Binding Sites; Carbenoxolone; Corticosterone; Drug Synergism; In Vitro Techniques; Leydig Cells; Male; Mineralocorticoid Receptor Antagonists; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Mineralocorticoid; RNA, Messenger; Spironolactone; Testosterone

Recently, we identified a novel putative nuclear receptor in colonic crypt cells distinct from both mineralocorticoid receptor and glucocorticoid receptor, with high affinity for 11-dehydrocorticosterone (11-DHB) (33). In the present study, competitive nuclear binding assays demonstrated that this site has a unique steroid binding specificity that distinguishes it from other steroid receptors. Western blot analysis showed the presence of 11beta-hydroxysteroid dehydrogenase-2 (11betaHSD2) but not 11betaHSD1 in colonic crypt cells and showed that 11betaHSD2 was present in the nuclear pellet. Differences in steroid specificity between the putative DHB receptor and inhibition of 11betaHSD activity indicate that binding is not to the enzyme. Furthermore, modified Chinese hamster ovary cells transfected with the 11betaHSD2 gene express nuclear 11betaHSD2 but not a nuclear DHB binding site. In conclusion, these data support the existence of a novel nuclear DHB receptor in rat colon that is distinct from the classic steroid receptors and from both 11betaHSD1 and 11betaHSD2.

Topics: 11-beta-Hydroxysteroid Dehydrogenases; Animals; Carbenoxolone; Cell Nucleus; Cells, Cultured; CHO Cells; Colon; Corticosterone; Cricetinae; Culture Media, Conditioned; Hydroxysteroid Dehydrogenases; Intestinal Mucosa; Male; Rats; Rats, Sprague-Dawley; Recombinant Proteins; Spironolactone; Substrate Specificity; Transfection

In vivo, corticosterone and 11-dehydrocorticosterone are interconverted in the liver and possibly kidney by 11 beta-hydroxysteroid dehydrogenase. In an effort to evaluate the relevance of this reversible reaction in relation to urinary sodium and potassium excretion, we investigated the effects of 11-dehydrocorticosterone in the presence and absence of carbenoxolone, a potent inhibitor of the oxidative component of 11 beta-hydroxysteroid dehydrogenase, and compared them with the effects of similar doses of corticosterone in carbenoxolone-treated rats. All experiments were performed on adrenalectomized male rats. Here we describe that in carbenoxolone-treated rats 11-dehydrocorticosterone and corticosterone display antinatriuretic activity, although under the conditions of this study 11-dehydrocorticosterone is a more potent sodium retainer than its parent steroid corticosterone. In addition, the antinatriuretic effects of 11-dehydrocorticosterone (like the antinatriuretic effects of corticosterone in carbenoxolone-treated rats) were blocked by the specific antimineralocorticoid RU28318.

Topics: Adrenalectomy; Animals; Carbenoxolone; Corticosterone; Creatinine; Male; Mineralocorticoid Receptor Antagonists; Natriuresis; Potassium; Rats; Rats, Sprague-Dawley; Spironolactone