Direct action of aldosterone on transmembrane 22Na efflux from arterial smooth muscle. Rapid and delayed effects

Acute subcutaneous (s.c.) administration of aldosterone increases ex vivo 22Na efflux from rat tail artery smooth muscle, which appears to be due to a specific action on mineralocorticoid receptors. Indeed, this effect is blocked by the antimineralocorticoid compounds RU 28318 [17 beta-hydroxy-3-oxo,7 alpha-propyl(17 alpha)-pregn 4-ene, 21 potassium carboxylate] and spironolactone. The specific glucocorticoid receptor agonist RU 26988 [11 beta,17 beta-dihydroxy-17-(1-propynyl) androesta-1,4,6 trien-3-one] does not modify 22Na efflux. We show here that aldosterone has, at physiological concentrations, a mineralocorticoid specific stimulating effect on passive and sodium pump dependent transmembrane movements of sodium from the rat tail artery smooth muscle. Aldosterone exerts two types of action on sodium transport: 1) a delayed stimulation of ouabain-dependent 22Na efflux and ouabain-independent 22Na efflux, which are completely blocked by actinomycin D; and 2) a very rapid increase of passive 22Na efflux, which is insensitive to actinomycin D and therefore does not seem to depend on transcription of genomic information.