Studies were performed, using a synthetic glucocorticoid, RU 28362, that has negligible binding to aldosterone receptors, to examine whether the effect of glucocorticoids on the electrical properties of rat distal colon involves a specific mechanism or crossover binding to aldosterone receptor sites. Compared with control, RU 28362, in a dose of 70 micrograms.100 g body wt-1.day-1, increased transepithelial potential differences (VT) twofold and the equivalent short-circuit current (ISC) threefold; epithelial resistance (RT) was reduced 25%. These changes were qualitatively similar to, but less than, the changes induced by the same dose of aldosterone. The effects of dexamethasone in the same dose were indistinguishable from the changes caused by aldosterone. The results of cell-impalement studies corresponded to whole epithelial changes; RU 28362 induced a small increase in basolateral potential difference, from -43 +/- 2 to -45 +/- 1 mV, and a fall in apical potential difference, from 40 +/- 2 to 36 +/- 1 mV, but these effects on cell membrane voltage were less than caused by either aldosterone or dexamethasone. In contrast to the marked inhibitory action of amiloride to reduce VT in aldosterone- and dexamethasone-treated animals, this sodium channel blocker had no effect on VT in RU 28362-treated animals. Similarly, while spironolactone caused marked inhibition of the changes in VT, RT, and ISC induced by aldosterone, the inhibitory action on tissue from RU 28362-treated animals was slight or absent. These results suggest that glucocorticoids have a specific aldosterone receptor-independent action on the electrical properties of the large intestine.