Effect of Ethacrynic Acid on Plasma Renin Activity during Supine Exercise in Normal Subjects

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Abstract
Plasma renin activity, clearances of inulin(cin)and para‐aminohippuric acid(cpah), free water clearance(ch2o)and urinary excretion of sodium and potassium were measured in 6 normal subjects at rest and during exercise in the supine position on a bicycle ergometer. The mean work load was 667 kpm/min and the duration of exercise 45 min. Ethacrynic acid, 50 mg, was injected i.v. at the start of exercise. Ethacrynic acid did not influence the normally occurring decrease in Cpahand Cinduring exercise but abolished the renal concentration mechanism, indicating an inhibition of sodium reabsorption in the ascending loop of Henle. The urinary sodium cxcrction increased markedly, indicating an increased load of sodium in distal tubules. This was coincident with increased plasma renin activity. The findings indicate that changes in plasma sodium concentration or sodium load in the distal tubules are of minor importance for the increase in plasma renin activity during exercise.