Site of action of torasemide in man

The effect of torasemide, a new orally and parenterally active diuretic agent, on the renal mechanisms of dilution and concentration was studied in 6 healthy volunteers. The experimental conditions included water and osmotic diuresis. Torasemide caused maximal chloruresis and natriuresis during the 20–40 min after administration. The effect was more pronounced under osmotic diuresis and persisted throughout the 100 min of those experiments. A distinct effect both on free water clearance ( \(CL_{H_2 0}\) ) during water diuresis and tubular reabsorption of solute free water ( \(T_{cH_2 0}\) ) during osmotic diuresis strongly suggests that the major site of action of torasemide is the ascending limb of the loop of Henle. Comparison with furosemide under osmotic diuresis indicates longer abolition of \(T_{cH_2 0}\) /GFR by torasemide in keeping with the fact that its half-life is 2- to 3-times longer than that of furosemide.