PROXIMAL TUBULAR REJECTION OF SODIUM BY FUROSEMIDE

¹ Renal-Hypertension-Electrolyte Division, Department of Internal Medicine, University of Iowa, and Medical Service, Veterans Administration Hospital, Iowa City, Iowa

In studies in acid-loaded dogs, we gave chlormerodrin for sodium reabsorption blockade in the loop of Henle and chlorothiazide to block sodium reabsorption in the cortical diluting segment of the nephron. After maximal diuresis was obtained with these drugs, furosemide was added in order to study the proximal effects of the drug. In antidiuretic animals, furosemide was administered after maximal chlormerodrin diuresis was achieved. Calculations of proximal and distal sodium reabsorption by an estimate of the sodium delivered to the distal tubule (loop of Henle and more distal portions of the nephron) indicate clearly that furosemide increases proximal sodium rejection in both the diuretic and antidiuretic state. If one uses the likely assumption that 70% of the filtered sodium is reabsorbed proximally in both of these preparations, these studies suggest that all three diuretics have proximal sites of action as well as their acknowledged distal ones.