RENAL EFFECT OF ETHACRYNIC ACID IN CHICKENS, A SPECIES WITH A SMALL COUNTERCURRENT SYSTEM

¹ Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, Florida

Since a prominent part of action of ethacrynic acid in the dog and in man is assigned to the inhibition of Na⁺ transport in the ascending loop of Henle, it was of interest to determine the effect of this drug in the chicken, a bird with poorly developed loops of Henle. Standard clearance methods were used. In the chicken, as in the dog, ethacrynic acid produces a large saluresis with the urine isosmotic with plasma. A single i.v. dose of 1 mg/kg is maximally effective, resulting in urinary excretion of 47% of filtered Cl^-. By comparison, the i.v. administration of mercaptomerin (4 mg/kg of Hg), hydrochlorothiazide (5 mg/kg) and aminophylline (27 mg/kg) causes an excretion of 9 to 11% of filtered Cl^-. Ouabain is the only agent tested that is as active as ethacrynic acid. Because in the presence of only a rudimentary counter-current multiplier system the contribution of the ascending limb of the loop of Henle to the reabsorption of filtrate should be relatively small, the major effect of ethacrynic acid responsible for the large urinary Na⁺ and Cl^-excretion should be located outside the loop of Henle.