Renocortical expression of renin and of cyclooxygenase-2 in response to angiotensin 11 AT1 receptor blockade is closely coordinated but not causally linked

Based on recent evidence that renin gene and cyclooxygenase-2 (COX-2) expression in the rat kidney cortex increase in parallel under a variety of conditions, this study aimed to characterize the causal linkage between COX-2 and renin expression. Therefore, we semi-quantitated renocortical renin and COX-2 gene expression when the renin-angiotensin system (RAS) was inhibited by the angiotensin II (Ang II) AT1 receptor antagonist candesartan (15 mg/kg per day) and when COX-2 activity was blocked by celecoxib (20 mg/kg twice a day) in three rat strains (Sprague-Dawley, WKY and SHR) at ages of 5, 9 and 15 weeks. We observed that candesartan increased renin mRNA in all rats at all ages, the amplitude of stimulation being inversely related to age. Candesartan increased COX-2 mRNA in all three strains at 5 weeks, and in SID and WKY rats also at 9 weeks. In 9-week-old SUR and in 15-week-old rats of all three strains candesartan did not influence COX-2 mRNA levels. For all rat strains, strain-specific strong linear correlations existed between renocortical COX-2 and renin mRNA levels, both with and without candesartan treatment. The additional feeding of candesartan-treated rats with celecoxib did not change renin mRNA or COX-2 mRNA levels, whilst the renal excretion of sodium and renal cortical prostaglandin E-2 concentration decreased by 26% and 60%, respectively. In summary, these findings, obtained when the renin system was activated by AT(1) receptor blockade, indicate that Ang II is not required to stimulate COX-2 expression and that COX-2 activity is not required to stimulate renin expression. However, the renocortical expression of renin and of COX-2 appear to be highly coordinated under basal conditions and during inhibition of RAS, suggesting the existence of a common denominator for renin and COX-2 expression that remains to be elucidated.