Regional Expression of Cyclooxygenase Isoforms in the Rat Kidney in Complete Unilateral Ureteral Obstruction

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Abstract
The cyclooxygenase (COX) pathway is activated in unilateral ureteral obstruction (UUO), contributing to renal hemodynamic alterations in different regions of the kidney. After the release of 24-hour UUO cortical vasoconstriction occurs but medullary hyperemia is seen. We examined the expression of the 2 COX isoforms COX-1 and COX-2 in different regions of the kidney in rats subjected to UUO. Clearance experiments were performed after ureteral obstruction release in rats with 24-hour UUO or sham operated rats. COX-1 and COX-2 expression in the cortex and medulla were examined by Western blot analysis and immunohistochemistry. After UUO release the glomerular filtration rate and renal plasma flow were markedly lower in post-obstructed kidneys than in contralateral kidneys or in kidneys in sham operated rats (p <0.001). Western blot analysis showed that COX-2/β-actin in the cortex of the obstructed kidney was 0.28 ± 0.02 densitometry units, significantly lower than 0.67 ± 0.12 densitometry units in the contralateral unobstructed kidney. In contrast, COX-2/β-actin in the outer and inner medullae of the obstructed kidney was 7.85 ± 1.09 and 2.51 ± 0.14 densitometry units, significantly greater than 3.03 ± 0.22 and 0.66 ± 0.14 densitometry units, respectively, in the contralateral unobstructed kidney. The expression of COX-1/β-actin in the obstructed kidney was similar to that in the contralateral unobstructed kidney in the cortex and medulla. Renal COX-2 expression is markedly altered in UUO. Decreased cortical expression of COX-2 and markedly increased expression in the medulla may contribute to disparate regional hemodynamic alterations in UUO.