Evidence for concerted effects of aldosterone on a target sodium-transporting epithelium.

The sodium-transporting activity of toad skin is stimulated in vitro with aldosterone in the absence of energy-providing substrate; it can be stimulated further upon addition of glucose after prolonged (overnight) incubation. The magnifying effect exerted by glucose in these conditions could be blocked by inhibitors of ribonucleic acid and protein biosynthesis. In addition, exposure to cycloheximide prevented the increase in thermodynamic affinity resulting from aldosterone treatment. A synthetic 19-nor steroid, (RU 24411), dimethyl-2,2-hydroxy-21-nor-19-pregnene-4-dione-3,20, also stimulated sodium transport by toad skin incubated in the absence of glucose, but there was no magnifying effect of this substrate. Furthermore, there was no change in thermodynamic affinity with RU 24411. Therefore, the magnifying effect seen with glucose and the increase in thermodynamic affinity are not necessarily integral parts of the response of sodium-transporting epithelial to "mineralocorticoids."