| Abstract: | There exist altogether four stereoisomers of ascorbic acid. Erythorbic acid (D-isoascorbic acid) differs in the spatial configuration at carbon 5 and has less than 5 per cent of biological vitamin C activity. In guinea pigs, depending on an exogenous supply of ascorbic acid, a possible interaction of erythorbic acid with absorption, transport through the cell membranes at the tissue level, or with catabolism of ascorbic acid has been investigated. After oral administration, results suggest no difference in absorption of these two compounds from the intestine, whereas uptake by the tissues was approximately four to one in favour of ascorbic acid. Feeding experiments with erythorbic acid indicate the availability of ascorbic acid being diminished by 40-60% when administered together with erythorbic acid. Kinetic data on the catabolism of ascorbic acid showed a significant reduction in half-life (50% of the dose excreted) of the vitamin caused by administration of erythorbic acid. The results suggest the oxidative destruction of ascorbic acid in the liver being significantly accelerated. Thus, ingestion of erythorbic acid interacts with newly introduced ascorbic acid by enforcing the breakdown of ascorbic acid. Implications of these findings for the metabolism, availability and nutritional status of ascorbic acid in humans will be discussed. |
