Blunting of furosemide diuresis by aspirin in man.

Experiments were performed on humans to study the blunting on the diuretic action of furosemide by prostaglandin synthetase inhibitors. Maximal water diuresis was instituted. At the peak of urine flow, clearance periods were performed during baseline conditions and repeated after the injection of aspirin and, subsequently, of furosemide. Control subjects did not receive aspirin. Urine flow rate (V), Cosm, and Na excretion (UNa) . V were significantly lower when the administration of the diuretic had been preceded by that of aspirin. In the absence of furosemide, however, aspirin did not influence renal hemodynamics nor Na and water reabsorption. Therefore, the same experimental protocol was repeated in paired experiments where each normal subject served as his own control, being studied twice, in the presence and absence of aspirin, respectively. The average changes in water and Na excretion induced by furosemide were not different when the patients were pretreated with aspirin as compared with those measured in the absence of prostaglandin inhibition. Changes occurring in individual experiments were significantly correlated (r = 0.95, P less than 0.01) with those in calculated furosemide clearance. Since aspirin, indomethacin, and meclophenamate are secreted by the organic acid transport system of the proximal tubule, competition for a common secretory mechanism, rather than prostaglandin inhibition, could mediate the blunting of furosemide diuresis.