Cyclooxygenase inhibitors increase Na-K-2Cl cotransporter abundance in thick ascending limb of Henle's loop

Cyclooxygenase inhibitors, such as indomethacin and diclofenac, have well-d escribed effects to enhance renal water reabsorption and urinary concentrat ing ability. Concentrating ability is regulated in part at the level of the thick ascending limb of Henle's loop, where active NaCl absorption drives the countercurrent multiplication mechanism. We used semiquantitative immun oblotting to test the effects of indomethacin and diclofenac, given over a 48-h period, on the expression levels of the ion transporters responsible f or active NaCl transport in the thick ascending limb. Both agents strongly increased the expression level of the apical Na-K-2Cl cotransporter in both outer medulla and cortex. Neither agent significantly altered outer medull ary expression levels of other thick ascending limb proteins, namely, the t ype 3 Na/H exchanger (NHE-3), Tamm-Horsfall protein, or alpha 1- or beta 1- subunits of the Na-K-ATPase. Administration of the EP3-selective PGE(2) ana log, misoprostol, to indomethacin-treated rats reversed the stimulatory eff ect of indomethacin on Na-K-2Cl cotransporter expression. We conclude that cyclooxygenase inhibitors enhance urinary concentrating ability in part thr ough effects to increase Na-K-2Cl cotransporter expression in the thick asc ending limb of Henle's loop. This action is most likely due to elimination of an EP3-receptor-mediated tonic inhibitory effect of PGE(2) on cAMP produ ction.