CORTICOSTEROID RECEPTOR MESSENGER-RNA EXPRESSION IS UNAFFECTED BY CORTICOSTEROIDS IN RAT-KIDNEY, HEART, AND COLON

Hormones can regulate the expression of their own receptor. We have ex amined whether adrenalectomy (ADX) and hormone replacement by physiolo gical doses of aldosterone or dexamethasone could modulate the express ion of glucocorticoid receptor (GR) or mineralocorticoid receptor (MR) at the mRNA level in the rat kidney, distal colon, and heart. Adult r ats were adrenalectomized and received or did not receive an infusion of aldosterone (5 mu g . 100 g(-1). day(-1)) or dexamethasone (10 mu g . 100 g(-1). day(-1)). No significant change in steady-state levels o f both MR and GR mRNA was detectable by using ribonuclease (RNase) pro tection assay (RPA) after either ADX or hormone replacement. Because t he kidney is heterogeneous with regard to MR expression, RPA was adapt ed for measurements on microdissected nephron segments. GR mRNA is exp ressed at comparable levels all along the nephron, whereas MR mRNA is restricted to the distal nephron. No effect of ADX on GR and MR mRNA l evels was detected in any nephron segment that was either aldosterone sensitive or insensitive. In situ hybridization confirmed the absence of corticosteroid-dependent modulation of MR mRNA in all kidney cell t ypes. We conclude that variations of corticosteroid status do not affe ct MR and GR mRNA steady-state levels in heart, colon, and kidney and thus do not participate to the functional adaptations that are known t o depend on hormonal status.