Corticosteroid receptor mRNA expression is unaffected by corticosteroids in rat kidney, heart, and colon

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Abstract
Hormones can regulate the expression of their own receptor. We have examined whether adrenalectomy (ADX) and hormone replacement by physiological doses of aldosterone or dexamethasone could modulate the expression of glucocorticoid receptor (GR) or mineralocorticoid receptor (MR) at the mRNA level in the rat kidney, distal colon, and heart. Adult rats were adrenalectomized and received or did not receive an infusion of aldosterone (5 micrograms.100 g-1.day-1) or dexamethasone (10 micrograms.100 g-1.day-1). No significant change in steady-state levels of both MR and GR mRNA was detectable by using ribonuclease (RNase) protection assay (RPA) after either ADX or hormone replacement. Because the kidney is heterogeneous with regard to MR expression, RPA was adapted for measurements on microdissected nephron segments. GR mRNA is expressed at comparable levels all along the nephron, whereas MR mRNA is restricted to the distal nephron. No effect of ADX or GR and MR mRNA levels 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 types. We conclude that variations of corticosteroid status do not affect MR and GR mRNA steady-state levels in heart, colon, and kidney and thus do not participate to the functional adaptations that are known to depend on hormonal status.