Mechanism of enhanced eicosanoid production by isolated glomeruli from rats with bilateral ureteral obstruction

Cyclooxygenase 2 inhibition exacerbates AQP2 and pAQP2 downregulation independently of V2 receptor abundance in the postobstructed kidney

Previously we demonstrated that ANG II receptor (AT1R) blockade attenuates V2 receptor (V2R), AQP2, and pS256-AQP2 downregulation in the postobstructed kidney and partially reverses obstruction-induced inhibition of cAMP generation and cyclooxygenase 2 (COX-2) induction. Therefore, we speculated whether the effects of AT1R blockade on V2R and the vasopressin-regulated pathway are attributable to attenuated COX-2 induction. To examine this, rats were subjected to 24-h bilateral ureteral obstruction (BUO) followed by 48-h release and treated with the COX-2 inhibitor parecoxib or saline. Control rats were sham-operated. Parecoxib treatment significantly reduced urine output 24 h after release of BUO whereas urine osmolality and solute-free water reabsorption was comparable between saline- and parecoxib-treated BUO rats. Immunoblotting revealed a significant decrease in AQP2 and pS256-AQP2 abundance to 20 and 23% of sham levels in parecoxib-treated BUO rats compared with 40 and 55% of sham levels in saline-treated BUO rats. Immunohistochemistry confirmed the exacerbated AQP2 and pS256-AQP2 downregulation in parecoxib-treated BUO rats. Finally, parecoxib treatment had no effect on V2R downregulation and the inhibited, vasopressin-stimulated cAMP generation in inner medullary membrane fractions from the postobstructed kidney. In conclusion, COX-2 inhibition exacerbates AQP2 and pS256-AQP2 downregulation 48 h after release of 24-h BUO independently of V2R abundance and vasopressin-stimulated cAMP generation. The results indicate that COX-2 inhibition does not mimic AT1R blockade-mediated effects and that AT1R-mediated AQP2 regulation in the postobstructed kidney collecting duct is independent of COX-2 induction.

Angiotensin II stimulates cyclooxygenase-2 mRNA expression in renal tissue from rats with kidney failure

We have shown increased cyclooxygenase-2 (COX-2) expression in rats with kidney failure. Increased angiotensin II concentration, hypertension, and renal mass reduction have been described during development of kidney failure. Thus we explored each of these mechanisms, because any one of them could be responsible for COX-2 induction. Kidney failure increased systolic blood pressure from 104 +/- 5 to 138 +/- 2 mmHg, urinary PGE(2) from 74 +/- 17 to 185 +/- 25 ng/24 h, and COX-2 expression from 0.06 +/- 0.04 to 0.17 +/- 0.03 arbitraty units (AU). Treatment of the rats with ramipril or losartan prevented the increase in blood pressure, urinary PGE(2), and COX-2 expression in the rats with kidney failure. Infusion of angiotensin II increased blood pressure from 101 +/- 6 to 132 +/- 6 mm Hg, urinary PGE(2) excretion from 62 +/- 15 to 155 +/- 17 ng/24 h, and COX-2 expression from 0.23 +/- 0.01 to 1.6 +/- 0.3 AU. When the angiotensin II-infused rats were treated with nitrendipine, blood pressure decreased from 132 +/- 6 to 115 +/- 2 mm Hg, and urinary PGE(2) excretion decreased from 152 +/- 18 to 97 +/- 12 ng/24 h, whereas COX-2 expression was 1.6 +/- 0.7 and 1.7 +/- 0.5 AU for rats with and without nitrendipine. Blood pressure of the rats with renal pole resection was similar to that in sham rats (97 +/- 7 and 91 +/- 4 mmHg, respectively), whereas COX-2 expression was increased in rats with renal pole resection, from 0.06 +/- 0.04 to 0.12 +/- 0.03 AU. We suggest that in kidney failure, the increase in angiotensin II concentration regulates COX-2 expression, thereby increasing prostaglandin synthesis, which contributes to the development of kidney failure.

Immunohistochemical and functional correlations of renal cyclooxygenase-2 in experimental diabetes

Prostaglandins (PGs) generated by the enzyme cyclooxygenase (COX) have been implicated in the pathological renal hemodynamics and structural alterations in diabetes mellitus, but the role of individual COX isoenzymes in diabetic nephropathy remains unknown. We explored COX-1 and COX-2 expression and hemodynamic responses to the COX-1 inhibitor valeryl salicylate (VS) or the COX-2 inhibitor NS398 in moderately hyperglycemic, streptozotocin-diabetic (D) and control (C) rats. Immunoreactive COX-2 was increased in D rats compared with C rats and normalized by improved glycemic control. Acute systemic administration of NS398 induced no significant changes in mean arterial pressure and renal plasma flow in either C or D rats but reduced glomerular filtration rate in D rats, resulting in a decrease in filtration fraction. VS had no effect on renal hemodynamics in D rats. Both inhibitors decreased urinary excretion of PGE(2). However, only NS398 reduced excretion of thromboxane A(2). In conclusion, we documented an increase in renal cortical COX-2 protein expression associated with a different renal hemodynamic response to selective systemic COX-2 inhibition in D as compared with C animals, indicating a role of COX-2-derived PG in pathological renal hemodynamic changes in diabetes.