Possible Nongenomic Actions of Aldosterone and Other Steroid Hormones
Recent studies suggest that many steroids, including aldosterone, elicit not only slowly developing genomic effects that have a latency of 60 to 90 minutes and require gene transcription and synthesis of new proteins, but also rapid nongenomic effects that take place in a few seconds or minutes.
These nongenomic actions are believed to be mediated by binding of steroids to cell membrane receptors that are coupled to second messenger systems, similar to those used for peptide hormone signal transduction. For example, aldosterone has been shown to increase formation of cAMP in vascular smooth muscle cells and in epithelial cells of the renal collecting tubules in less than two minutes, a time period that is far too short for gene transcription and synthesis of new pro-teins. In other cell types, aldosterone has been shown to rapidly stimulate the phosphatidylinositol second messenger system. However, the precise structure of receptors responsible for the rapid effects of aldos-terone has not been determined, nor is the physiolog-ical significance of these nongenomic actions of steroids well understood.