Glucocorticoid and mineralocorticoid regulation of angiotensin II type 1 receptor binding and inositol triphosphate formation in WB cells.

Mineralocorticoids, glucocorticoids, and angiotensin II (AngII) act cooperatively to maintain body fluid homeostasis. Mineralocorticoids, such as aldosterone and deoxycorticosterone-acetate (DOCA), function synergistically with AngII in the brain to increase salt appetite and blood pressure. In addition, glucocorticoids increase AngII-induced drinking and pressor responses and may also facilitate the actions of aldosterone on salt appetite. The AngII Type 1 (AT1) receptor mediates many of the physiological and behavioral actions of AngII. This receptor is coupled to the G-protein Gq, which mediates AngII-induced inositol triphosphate (IP3) formation. The WB cell line, a liver epithelial cell line that expresses the AT1 receptor, was used to examine the cellular basis of glucocorticoid and mineralocorticoid regulation of AT1 function. In this study corticosterone and dexamethasone treatments increased the number of AT1 receptors by activating the glucocorticoid receptor (GR). This increase in AT1 binding resulted in enhanced AngII-stimulated IP3 formation. However, only supraphysiological doses of aldosterone or DOCA increased AT1 binding, and this effect also was mediated by GR activation. Furthermore, despite evidence that mineralocorticoids and glucocorticoids function together to increase AngII-stimulated actions in vivo, aldosterone and dexamethasone did not act synergistically to affect AT1 binding, Gq expression, or IP3 formation. These results indicate that GR activation, and the subsequent increases in AT1 binding and in AngII-stimulated IP3 formation, may represent a cellular mechanism underlying the synergy between adrenal steroids and AngII.