Regulation of angiotensin II receptor subtypes by dexamethasone in rat mesangial cells.

ABSTRACT

The objective of this study was to examine the role of dexamethasone on the expression of angiotensin II (Ang II) receptors in cultured rat mesangial cells. Dexamethasone caused concentration- and time-dependent decreases in 125I-[Sar1,Ala8]Ang II binding that were prevented by glucocorticoid receptor inhibition with mifepristone. A lag time of 24 hours and a dexamethasone concentration of at least 10 nmol/L were necessary for this effect to occur. Dexamethasone-induced reduction of 125I-[Sar1,Ala8]Ang II binding resulted from decreased Ang II type 1 (AT1) receptor density. No change in the apparent dissociation constant was observed. Dexamethasone also markedly inhibited Ang II-dependent inositol phosphate accumulation. Both reverse transcription-polymerase chain reaction and Northern blot analysis using specific short probes from the 3' noncoding region of the cDNA demonstrated the presence of AT1A and AT1B receptor mRNAs in rat mesangial cells, with a slight predominance of AT1B. Therefore, we studied the effect of dexamethasone on the expression of these two subtypes in rat mesangial cells. Dexamethasone produced a time-dependent decrease of AT1B receptor mRNA that was apparent after 6 hours of incubation, whereas AT1A receptor mRNA did not change. Mifepristone also suppressed the dexamethasone-induced decrease in AT1B receptor mRNA. In conclusion, glucocorticoids diminish Ang II receptor density at the mesangial cell surface through a mechanism that implies successive interaction with the glucocorticoid receptor and specific reduction in AT1B receptor mRNA expression. This differential regulation of both AT1 receptor subtypes might allow glucocorticoids to exert adjusted effects in their various target tissues.