Studies on the metabolic conversion of ascorbate.
In the intact animal guinea pigs metabolize (1-14C)ascorbic acid much faster to (14C)carbon dioxide (peak exhalation at 30 min) than rats (peak exhalation at 2 to 3 h) following single oral administration, but total excretion was comparable. This finding might be related to the differences in the absorption mechanism of ascorbic acid in these species. The large difference in retention capacity of ascorbic acid in the liver is suggested to be due to multiple recirculation of ascorbic acid in the guinea pig when compared to the rate. Homogenate preparations of rat stomach, small intestine or liver as well as cultured intestinal microbial flora did not cause metabolic degradation on incubation with (1-14C)ascorbic acid to (14C)carbon dioxide. It is therefore suggested that the observed excretion of (14C)carbon dioxide is due to spontaneous non-enzymatical reaction in liver and possible other tissues. Analysis of ascorbic acid metabolites formed on incubation by analytical isotachophoresis suggests that ascorbic acid is a rather stable substrate whereas dehydroascorbate and 2,3-diketogulonic acid are rapidly degraded. This allows the assumption that in vivo metabolism of ascorbic acid might not involve dehydroascorbic acid. Our data do not support the hypothesis that ascorbic acid undergoes presystemic metabolism to carbon dioxide in the intestinal wall.
D015083:2,3-Diketogulonic Acid / Q000378:metabolism; D000818:Animals; D001204:Ascorbate Oxidase / Q000378:metabolism; D001205:Ascorbic Acid / Q000378:metabolism*; D001419:Bacteria / Q000378:metabolism; D002245:Carbon Dioxide / Q000096:biosynthesis; D003683:Dehydroascorbic Acid / Q000378:metabolism; D005243:Feces / Q000032:analysis; D005753:Gastric Mucosa / Q000378:metabolism; D006168:Guinea Pigs; D007421:Intestine, Small / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
D002245:Carbon Dioxide; D015083:2,3-Diketogulonic Acid; D001204:Ascorbate Oxidase; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid