Effect of potassium loading on metabolism of aldosterone in rats

Abstract

Thirty minutes after subcutaneous injection of 3H-aldosterone, the distribution of 3H radioactivity in the liver, kidney, small intestine, and plasma of rats who had been potassium-loaded for 2 or 4 days was demonstrated to be significantly altered. The total radioactivity (disintegrations per minute per gram) in both the homogenate and cytosol fractions of both the liver and kidney were markedly increased in rats maintained on the high-potassium diet. Of marked interest, both the quantities and percentages of nonextractable polar derivatives of aldosterone were significantly increased in these tissues during the 4 days of potassium loading. However, significantly smaller quantities of 3H radioactivity were demonstrated to be present in the small intestine of the potassium-loaded rats. Total plasma radioactivity and the quantities of the polar metabolites of aldosterone in the plasma were also significantly elevated in the potassium-loaded rats. The percentage of nonextractable radioactivity in the plasma also increased from 42% to 54% by 4 days of potassium loading. Interestingly, the halflife for aldosterone in the plasma, 11 min, was not altered following the potassium loading. The rates of biliary excretion of radiometabolites of aldosterone were not different from those of the control rats. These preliminary findings suggest that the overall metabolism of aldosterone is altered in potassium-loaded rats, leading to increased quantities of the polar metabolites of aldosterone in the plasma, the liver, and particularly in the target tissue, the kidney. These findings might indicate a relationship between the alteration in the metabolism of aldosterone and the increased secretion of potassium ions by the kidney when adaptation to potassium loading occurs in rats.