Renal sites of action of azosemide.

Azosemide is a new monosulfamyl diuretic with potency and spectrum of effects similar to those of furosemide. Eight normal subjects were studied with clearance techniques during water loading and during hydropenia to assess azosemide's site of action. Solute free water reabsorption decreased from 3.1 +/- 0.3 to 0.5 +/- 0.9 ml/min after azosemide (p less than 0.05), indicating an effect of azosemide at the ascending limb of the loop of Henle. During water loading, despite significant 3.5-fold increases in fractional excretion of sodium and chloride, the per cent increase in free water formation, CH2O/CIN X 100 was not significantly changed by azosemide (10.4 +/- 1.4 control and 14.8 +/- 3.1 after azosemide). This unchanged CH2O/CIN X 100 occurred despite increased osmolal clearance after azosemide, from 2.6 +/- 0.4 to 3.8 +/- 0.4 ml/min (p less than 0.02), indicating that azosemide increased delivery of solute to the diluting segment. Evidence is discussed which implies that azosemide inhibits solute transport of the thick ascending limb of the loop of Henle, but may also affect more proximal sites.