Colonic Sodium-Potassium Adenosine Triphosphate Subunit Gene Expression: Ontogeny and Regulation by Adrenocortical Steroids*

Mineralocorticoids and glucocorticoids exhibit overlapping but distinct effects on transepithelial sodium transport in the descending colon. Na.K-ATPase, the major sodium pump, has been variously reported to be regulated by one or both classes of steroids. The present studies explore the ontogeny and steroidal regulation of Na.K-ATPase α- and β-subunit mRNA levels in the descending colon. In descending colon, subunit mRNA levels are low before birth, increasing to reach adult levels at approximately day 25. Dexamethasone treatment caused a rapid dose-dependent increase in colonic Na.K-ATPase subunit mRNA levels. The specific glucocorticoid RU26988 also increased subunit mRNA levels. Aldosterone administration, at doses adequate to yield a profound antinatriuresis, did not alter subunit mRNA levels. Carbenoloxone sodium produced an approximately 3-fold increase in subunit mRNA levels in intact but not adrenalectomized rats. We have demonstrated that Na.K-ATPase subunit gene expression is: 1) low in the fetal colon but achieves plateau levels by day 25; 2) acutely regulated by corticosteroids via type II rather than type I receptors; and 3) increased by carbenoxolone sodium, presumably as a result of increased occupancy of the type II receptor by corticosterone. (Endocrinology127: 32–38, 1990)