Abstract
Kidneys were removed from dogs 15 minutes to 2 hours after single i.v. injections of ethacrynic acid of 0.2, 1 or 5 mg/kg. The latter dose was determined by others to be maximally natriuretic in the dog. An adenosine triphosphatase (ATPase) fraction highly sensitive to ouabain in vivo, but with little sensitivity to ouabain in vitro, was prepared separately from cortex and outer medulla. Ethacrynic acid inhibited the ATPase activity from both portions of the kidney in a dose-dependent manner. The time of recovery of the enzyme activity was also dose dependent and was complete for the 5 mg/kg dose in 100 minutes. This correlates with the known short duration of diuresis induced by the drug. There was only little additional enzyme inhibition in kidneys pretreated with ouabain indicating that ethacrynic acid inhibited mainly the Na+ + K+ ATPase. This correlates with the previous observation that ethacrynic acid has no further natriuretic effect in a ouabain-inhibited kidney. In the rat treated with ethacrynic acid no enzyme inhibition was detected 15 to 25 minutes after doses of 1 or 5 mg/kg i.v.; similar doses are known to lack a diuretic effect in this species. Despite this fact, the enzyme preparation from rat kidneys was as sensitive to ethacrynic acid in vitro as was the preparation from dog kidney. The reversibility of Na+ + K+ ATPase inhibition by ethacrynic acid was tested in microsomal preparations which were highly sensitive to ouabain in vitro. In these preparations from the dog kidney, the inhibition by ethacrynic acid had irreversible characteristics according to Ackermann-Potter analysis, but the enzyme from rat kidneys behaved according to the kinetics of reversible inhibition, even after preincubation. We conclude that the natriuretic receptor for ethacrynic acid is likely to be the Na+ + K+ ATPase. The relative resistance of the rat to ethacrynic acid may be due to the reversible nature of the enzyme inhibition in this species.
Footnotes
- Received January 10, 1972.
- Accepted June 6, 1972.
- © 1972, by The Williams & Wilkins Company
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