Catabolism and Tissue Levels of Ascorbic Acid following Long-term Massive Doses in the Guinea Pig

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Abstract
Young male guinea pigs were fed diets containing either 2 g (control) or 86 g (experimental) of ascorbic acid/kg of diet for 275 days. The growth rate of experimental guinea pigs was significantly retarded as compared to the growth rate of the control guinea pigs. L-Ascorbic-1-14C acid was then injected intraperitoneally into both experimental and control guinea pigs to study the catabolism and excretion of the vitamin. Catabolism of the labeled ascorbic acid to respiratory 14CO2 was increased in experimental guinea pigs. This increased catabolism of an administered dose of L-ascorbic-1-14C acid was evident even after the guinea pigs were subjected to either a diet containing a minimal quantity of ascorbic acid (3 mg of ascorbic acid/kg) for 68 days or a diet devoid of ascorbic acid for 44 days. The amount of radioactivity recovered in the urine and feces was similar for both groups except for an increased urinary excretion of the label in experimental animals subjected to the totally deficient diet. The experimental animals maintained higher tissue stores of ascorbic acid than the control animals. However, this difference was significant only in the testes. When subjected to a totally ascorbic acid deficient diet the experimental animals were depleted of ascorbic acid at a faster rate than the control animals. The results are in agreement with the hypothesis that the regular ingestion of massive doses of ascorbic acid leads to accelerated ascorbic acid catabolism, i.e., systemic conditioning. The accelerated catabolism was not reversible by subnormal intakes of the vitamin.