Effects of Acute Changes in Acid-Base Balance on Renal Calcium Excretion in Dogs

Abstract

The effects of acute disturbances in acid-base balance on renal cation excretion were studied in dogs. Special attention was given to the excretory mechanism for calcium. Four different states were produced experimentally: respiratory acidosis, metabolic acidosis, metabolic alkalosis and compensated metabolic alkalosis. Additional experiments were carried out in normal and alkalotic animals subjected to calcium loading. Calcium reabsorption was found to vary directly with the filtered load of calcium. The increased excretion of calcium in acidosis appears to be due to an increase in filtered calcium. The percentage of reabsorption of filtered calcium was 98–99% in normal and acidotic dogs, but decreased to approximately 90% in animals made acutely alkalotic. However, the relative loss of water to calcium in the urine in acute alkalosis was decreased, resulting in an elevated renal threshold of retention of calcium in metabolic alkalosis. Data are included on the behavior of inorganic phosphate in the various states studied. Elevated carbon dioxide tension was associated with phosphate mobilization from the tissues regardless of whether or not the carbon dioxide excess was compensated for by extra alkali.