Distribution of prostaglandins E2 and 6-keto-F1 alpha production in dog kidneys

Renal changes induced by a cyclooxygenase-2 inhibitor during normal and low sodium intake

Cyclooxygenase-2 (COX-2) has been identified in renal tissues under normal conditions, with its expression enhanced during sodium restriction. To evaluate the role of COX-2-derived metabolites in the regulation of renal function, we infused a selective inhibitor (nimesulide) in anesthetized dogs with normal or low sodium intake. The renal effects elicited by nimesulide and a non-isozyme-specific inhibitor (meclofenamate) were compared during normal sodium intake. In ex vivo assays, meclofenamate, but not nimesulide, prevented the platelet aggregation elicited by arachidonic acid. During normal sodium intake, nimesulide infusion (n=6) had no effects on arterial pressure or renal hemodynamics but did reduce urinary sodium excretion, urine flow rate, and fractional lithium excretion. In contrast, nimesulide administration increased arterial pressure and decreased renal blood flow, urine flow rate, and fractional lithium excretion during low sodium intake (n=6). COX-2 inhibition reduced urinary prostaglandin E(2) excretion in both groups but did not modify plasma renin activity in dogs with low (8.1+/-1.1 ng angiotensin I. mL(-1). h(-1)) or normal (1.8+/-0.4 ng angiotensin I. mL(-1). h(-1)) sodium intake. Meclofenamate infusion in dogs with normal sodium intake (n=8) induced a greater renal hemodynamic effect than nimesulide infusion. These results suggest that COX-2-derived metabolites (1) are involved in the regulation of sodium excretion in dogs with normal sodium intake, (2) play an important role in the regulation of renal hemodynamic and excretory function in dogs with low sodium intake, and (3) are not involved in the maintenance of the high renin levels during a long-term decrease in sodium intake.

Comparative effect of PGE2 and PGI2 on renal function

Rapid degradation of prostacyclin (PGI2) inherent to its molecular structure has long been a major limitation in assessing the natriuretic effect of this prostaglandin. The recent availability of the stable PGI2 analogue iloprost now allows for a comparative study with prostaglandin E2 (PGE2). In the present study conducted in six anesthetized dogs, the intrarenal effects of two consecutive doses (1 and 4 ng x kg(-1) x min(-1)) of PGE2 on renal blood flow, glomerular filtration rate, and urinary sodium excretion were compared with the effects of two identical doses of iloprost. The selected doses of PGE2 were those producing a maximal natriuretic and vasodilator response without affecting mean arterial pressure. A washout period was allowed between administration of PGE2 and iloprost. PGE2 infusion significantly increased fractional sodium excretion from 0.69+/-0.1 to 2.79+/-1.1% and 4.27+/-1.2%% (P<.05), respectively. These changes in fractional sodium excretion induced by PGE2 were associated with significant increases in renal blood flow from 151.1+/-62 to 185+/-64.3 and 185.6+/-64.3 mL/min (P<.05), respectively; however, no significant alterations were seen in glomerular filtration rate, from 29.5+/-9.4 to 35.2+/-12.2 and 32.7+/-7.8 mL/min (NS), and mean arterial pressure, from 117.6+/-26 to 113.9+/-24.1 and 112.3+/-24.1 mm Hg (NS) during control and PGE2 infusion. At identical doses, sequential infusion of PGI2 had no effect on renal blood floww and glomerular filtration rate, producing natriuresis only at the highest dose, a fractional sodium excretion from 0.69+/-0.1 to 0.8+/-0.28 mm Hg (NS) and 1.05+/-0.34% (P<.05), respectively. In conclusion, the present study confirms that PGE2 exerts a natriuretic effect during increases in renal blood flow. In contrast, PGI2 had no hemodynamic effect, and the natriuresis was markedly blunted.