Effect of bumetanide and furosemide on the thick ascending limb of Henle's loop of rabbits and rats perfused in vitro.

Direct effects of bumetanide and furosemide on the thick ascending limb of Henle's loop (TALH) were compared by using the isolated tubules of rabbits and rats perfused in vitro. Both drugs, applied to the lumen, reversibly suppressed the lumen positive potential (PDt) of the rabbit TALH. Bumetanide also suppressed the PDt in the absence of Na+ where the NaCl of the artificial solutions was replaced by choline chloride. The efflux of 36Cl was also reduced by the addition of bumetanide to the perfusate. The dose-response analysis disclosed that bumetanide was 14 times as potent as furosemide. The onset and duration of bumetanide action was significantly longer than that of furosemide. Bumetanide also suppressed the PDt of the rat TALH when it was added to the perfusate.