Ascorbic acid synthesis in normal and drug-treated rats, studied with L-ascorbic-1-C14 acid.

It is known that, of all animal species studied, only man, other Primates, and the guinea pig are unable to synthesize ascorbic acid. Results obtained in rats, with radioactive glucose, indicate that ascorbic acid is synthesized by a fairly direct route from glucose (l-3), but no information has been available concerning the rate of synthesis and metabolism of ascorbic acid. Such information would make possible a comparison between the amount of ascorbic acid available each day by synthesis in the rat with that required daily in the diet of those species which are unable to synthesize ascorbic acid. Furthermore, the information would furnish a better understanding of the manner by which various organic compounds, particularly drugs such as Chloretone, paraldehyde, and barbiturates, markedly increase the urinary excretion of ascorbic acid (4). This increase in urinary excretion has been attributed to acceleration of synthesis, since the amounts found in the urine after the administration of the various compounds were far in excess of body stores of ascorbic acid estimated from chemical analysis of rat tissues (4). No quantitative data have been available, however, on the effect of these compounds either on the body pool or on the turnover rate of ascorbic acid. In the present investigation L-ascorbic-l-C14 acid was used to determine the rate of synthesis and metabolism of ascorbic acid in normal rats and in those receiving Chloretone and pentobarbital. The body pools of ascorbic acid in these animals were labeled with L-ascorbic-l-C14 acid, and the specific activity of urinary ascorbic acid was determined over various time intervals. From these data it was possible to estimate the turnover rate and the magnitude of the miscible body pool of ascorbic acid. The results indicate that the amount of ascorbic acid synthesized daily in rats is about the same as the amount required each day in the diet of guinea