CALCIUM-BINDING PROTEIN REGUCALCIN MESSENGER-RNA EXPRESSION IN THE KIDNEY CORTEX IS SUPPRESSED BY SALINE INGESTION IN RATS

The effect of adrenalectomy (ADX) or saline ingestion, which is a hype rtensive factor, on the expression of calcium-binding protein regucalc in mRNA in the kidney cortex of rats was investigated. The change of r egucalcin mRNA levels was analyzed by Northern blotting using rat live r regucalcin complementary DNA (0.9 kb of open-reading frame). Regucal cin mRNA was expressed in the kidney cortex but not the medulla. Rats were adrenalectomized, and 48 h later they were sacrificed. ADX caused a reduction of regucalcin mRNA levels in the kidney cortex, suggestin g that adrenal glands participate in the regulation of the mRNA expres sion. This reduction was not restored by the subcutaneous administrati on of dexamethasone with an effective dose (1 mg/kg body weight), whic h can stimulate kidney regucalcin mRNA expression. Regucalcin mRNA lev els in the kidney cortex of rats were markedly suppressed by the inges tion of saline for 7 days. The ADX-induced decrease of renal cortex re gucalcin mRNA levels was not appreciably restored by saline ingestion. Moreover, regucalcin mRNA levels in the kidney cortex of spontaneous hypertensive rats (SHR) were clearly decreased as compared with that o f control (Wistar-Kyoto) rats. Meanwhile, calcium content in the kidne y cortex was not significantly decreased by ADX or saline ingestion. T he present study suggests that the expression of regucalcin mRNA in th e kidney cortex of rats is suppressed by saline administration.