Effect of acute potassium loading on plasma renin and on urinary aldosterone in rats

The disposition of aldosterone radiometabolites in rats has been studied following iv [3H]aldosterone administration. Of injected [3H]-aldosterone, 0.31% is recovered in 24 h urine as free aldosterone and 0.08% as acid-labile conjugate. A simple, sensitive and reliable radioimmunoassay of free aldosterone has been developed and the effect of acute oral potassium loading (171, 513 or 769 mueq of KCl/100 g body weight) on 4 h aldosterone excretion, plasma renin concentration and sodium and potassium balance has been investigated. There was a positive correlation between log urinary aldosterone and potassium load (r = 0.92, P less than 0.001). Potassium induced a natriuresis which was correlated directly with the dose of potassium administered (r = 0.89, P less than 0.001). Ptasssium loading also increased plasma renin concentration which was correlated with the sodium excretion rate (r = 0.64, P less than 0.01). Prevention of a negative sodium balance during the 769 mueq potassium load was obtained by administration of 513 mueq sodium. In this experiment, plasma renin concentration increased little, whereas the aldosterone excretion rate was as high as during the 769 mueq potassium load without sodium addition.