An examination of the site and mechanism of action of torasemide in man.

Acute clearance studies were performed in normal subjects to determine the site and mechanism of action of torasemide (isopropyl-1-methyl-3 phenylamino-4 pyridil-3 sulphonyl-3-urea), a new diuretic agent, in the human kidney. The drug caused no change in glomerular filtration rate or effective renal plasma flow. Sodium excretion rose to 16% of filtered load, whereas there was a chloriuresis of 23%. During maximal water diuresis, the drug caused an increase in urine flow rate and a decrease in solute-free water clearance. Administration of the drug during hypertonic saline infusion into hydropenic subjects resulted in a marked decrease in water reabsorption from the collecting duct. Torasemide caused no change in phosphate excretion or in the percentage of filtered bicarbonate excreted, nor was urinary pH or net hydrogen ion excretion affected by the drug. The data suggest that the primary site of action of torasemide is the medullary portion of the ascending limb of the loop of Henle.