Regulation of renal cortical cyclooxygenase-2 in young rats

Cyclooxygenase-2 (COX-2) is involved in kidney morphogenesis and is transiently elevated in the immature kidney. In adult rats, renal cortical COX-2 expression is tonically suppressed by mineralocorticoids (MC) and glucocorticoids (GC) and induced by chronic salt restriction. Young rats have low levels of GC and are in a state of relative volume depletion. The present study was designed to investigate the mechanisms underlying elevated cortical COX-2 expression in the immature kidney. Supplementation of GC or MC suppressed cortical COX-2 expression in suckling rats. GC suppression was significantly, but not completely, prevented by either an MC receptor antagonist or a GC receptor antagonist. MC suppression was completely prevented by a mineralocorticoid receptor antagonist. Salt supplementation suppressed cortical COX-2 expression in a dose- and time-dependent pattern in the suckling rats. Cortical COX-2 expression in the weanling rats was upregulated by a low-salt diet and downregulated by a high-salt diet. These results suggest that relative volume depletion and reduced GC levels are involved in elevated cortical COX-2 expression in the immature rodent kidney.