Metabolism of Citric Acid, Potassium Citrate, Sodium Citrate and Calcium Citrate in the Rat

Abstract

The metabolism of citric acid and potassium, sodium and calcium salts of citrate in rats was investigated by single-dose oral administration. The per capita daily intake of citric acid and its salts in Japanese was estimated to be 37.78mg/kg by Ito et al., so 37.78mg/kg was chosen as the low dose and 1, 889mg/kg (50 times more) as the high dose. The urinary excretion of citrate, expiratory carbon dioxide (CO2), and the blood concentration and tissue distribution of citrate and/or its metabolites were investigated in fasting rats. A large proportion of administered citric acid and its salts was excreted within 24 hours, i. e., 76.7 to 88.9% as expiratory CO2, 3.8 to 11.2% in urine, and only a small amount in feces. In the rats given the high dose of potassium or sodium citrate, the absorption rate of citrate decreased while the urinary excretion increased. The times at which the urinary excretion of citrate and the blood concentration of citrate and/or its metabolites reached the maximum were different for citric acid and its salts. The absorption rates of citric acid and its salts were considered to be in the following order: citric acid>potassium citrate≥sodium citrate>calcium citrate. The distribution in the gastrointestinal tract was 37.6 to 64.3% after 30 minutes but less than 2.7% after 24 hours. Therefore, it is clear that a large proportion of administered citric acid and its salts is absorbed, metabolized and excreted mainly as CO2, and that the difference in metabolism between citric acid and its alkaline salts is negligible.