title: Spironolactone antagonism of aldosterone action on Na+ transport and RNA metabolism in toad bladder epithelium.
abstract: In earlier studies, aldosterone increased the incorporation of precursors into a class of cytoplasmic RNA with the characteristics of messenger RNA (mRNA), in toad bladder epithelium. In the present studies, this effect was analyzed further with a competitive antagonist, spironolactone (SC-9420). Paired hemibladders were labeled with 3H-uridine (30 min pulse - 140 min chase), with or without aldosterone (3.5 x 10(-8) M, 7 X 10(-8) M) in the presence or absence of SC-9420 (7 X 10(-6) M, 2.5 X 10(-5) M) at molar ratios of 200:1 to 280:1. Cytoplasmic RNA, either the total phenol-SDS extract or polyadenylated-RNA (poly(A)(+)-RNA) obtained by oligo-deoxythymidylate-cellulose (oligo(dT)-cellulose) chromatography was analyzed in linear 5 -- 20% sucrose gradients. Eight sets of experiments were completed in which the short-circuit current (scc) was monitored for 180 min and the incorporation of 3H-uridine (30 min pulse -- 150 min chase) was simultaneously determined on pools of epithelia from 5 to 10 hemibladders. The fractional change in scc correlated linearly with the fractional change in 3H-uridine of 12S cytoplasmic RNA (r=0.95, p less than 0.001). The poly(A)(+)-RNA fraction had no detectable rRNA or tRNA and gave a heterogeneous pattern, typical of mRNA, in the sucrose gradients. In the presence of exogenous aldosterone, SC-9420 inhibited the incorporation of 3H-uridine into poly(A)(+)-RNA (particularly 12S). These results support the inference that induction of mRNA mediates the action of aldosterone on Na+ transport.
mesh_terms: D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D004848:Epithelium / Q000378:metabolism; D000451:Mineralocorticoid Receptor Antagonists; D011061:Poly A / Q000378:metabolism; D012313:RNA / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013148:Spironolactone / Q000494:pharmacology*; D001743:Urinary Bladder / Q000378:metabolism*
chemical_list: D000451:Mineralocorticoid Receptor Antagonists; D011956:Receptors, Cell Surface; D011061:Poly A; D013148:Spironolactone; D000450:Aldosterone; D012313:RNA; D012964:Sodium