Total body and serum electrolyte composition in heart failure: the effects of captopril

We compared the long-term effects of captopril and placebo on patients with heart failure in a double blind crossover fashion. Serum and total body electrolytes were measured and the response to 6 week periods of treatment with captopril determined. During the placebo phase of the study, total body potassium was low at 92 +/- 14% of predicted normal (P less than 0.05) and total body sodium was high at 104 + 7% of predicted normal (P less than 0.05). Total body chlorine did not differ from predicted normal (99 + 12%). In those patients with active plasma renin concentrations above the normal range (greater than 50 microU ml-1) total body potassium was even more markedly deplete (85 + 13% of predicted normal). This group was also characterized by lower serum potassium and sodium concentrations and lower blood pressure. Total body potassium increased significantly on captopril, and the rise was greatest in those with the highest plasma renin concentrations during the placebo phase of the study. However, captopril had no significant effect on total body sodium and chlorine or weight indicating that no long-term natriuresis had occurred.