EFFECTS OF ETHACRYNIC ACID ON OXIDATIVE METABOLISM IN ISOLATED GLOMERULI

¹ Department of Pharmacology, University of Arizona Medical Center, Tucson, Arizona

The effects of ethacrynic acid on oxidative metabolism were studied in preparations of pure isolated rat kidney glomeruli obtained with the use of magnetic iron oxide. Ethacrynic acid inhibited the oxidation of oleate, succinate, glucose, lactate, citrate, aspartate and glutamate at concentrations of drug of 1x10^-4 M or greater, as measured by the conversion of labeled substrates to ¹⁴CO₂. A small but significant stimulation of oleic acid oxidation was observed at ethacrynic acid concentrations of less than 2x10^-5 M. Ethacrynic acid markedly inhibited oleic acid oxidation at a concentration of 5x10^-4 M while ouabain and furosemide at this concentration caused little or no inhibition. Modification of the aliphatic carbon-carbon double bond of the ethacrynic acid molecule by treatment with H₂S, H₂O₂ or hydrogenation resulted in a marked reduction or loss of the inhibitory properties of the compound. The inhibition of oleic acid oxidation could be prevented by the presence during incubation of a number of sulfhydryl-containing compounds. Later addition of a sulfhydryl compound to the incubation could only delay somewhat, but not prevent or overcome, the inhibition induced by ethacrynic acid. Ethacrynic acid is therefore a potent inhibitor of oxidative metabolism in isolated glomeruli and requires an intact activated double bond for inhibition. The inhibition can be blocked by agents containing free sulfhydryl groups, but whether the metabolic inhibition induced by the drug is due to its reactivity with such groups is not known.