BRADYKININ B-2 RECEPTOR ANTAGONIST INCREASES CHLORIDE AND WATER-ABSORPTION IN RAT MEDULLARY COLLECTING DUCT

This study tested the hypothesis that intrarenal kinins play a regulat ory role in electrolyte excretion by altering Cl- absorption in the co llecting duct. We measured Cl- and inulin concentrations in tubular fl uid samples obtained from medullary collecting ducts (MCD) of Dahl/Rap p salt-resistant (SR/ Jr) rats by microcatheterization of ducts of Bel lini before and after treatment with the bradykinin receptor antagonis t HOE-140. Tubular fluid was obtained from paired terminal inner medul lary (t-IMCD) and outer medullary (OMCD) collecting duct sites of the left kidney. HOE-140 (n = 7) or vehicle (n = 5) was infused intravenou sly, and the collections were repeated. HOE-140 did not alter glomerul ar filtration rate but decreased urine flow rate (P < 0.05) and absolu te and fractional Cl- excretion (P < 0.01). HOE-140 did not alter the fraction of filtered Cl- delivered (FDCl) to the OMCD but decreased FD Cl to the t-IMCD from 2.3 +/- 0.3 to 1.3 +/- 0.3% (P < 0.05). The frac tion of filtered Cl- absorbed per millimeter between the collection si tes was increased from 0.2 +/- 0.1 to 0.6 +/- 0.1% (P < 0.05). Fractio nal absorption of water along the MCD was also increased (P < 0.05). N o changes in excretory function or tubular Cl- or water absorption wer e observed in vehicle-treated rats. These studies show that kinin B-2 receptor blockade enhances Cl- and water absorption in the MCD, a find ing that supports a role of renal kinins in the regulation of NaCl and water excretion.