Ascorbic acid in thyroidectomized rats. I) Biosynthesis and catabolism

Thyroidectomized rats showed a decrease in ascorbic acid and dehydroascorbic acid, with almost no alterations in the diketogulonic acid in liver and kidney. Total ascorbic acid in urine was found to be increased, whereas glucuronic acid in urine decreased significantly. There were no significant changes in the activities of ascorbic acid synthesizing enzymes. Activities of the degrading enzymes were found to increase significantly in the liver, with no remarkable change in their activities in kidney. Daily administration of thyroxine for 10 days to thyroidectomized rats normalized the activities of dehydroascorbatase and 2,3 diketoaldonate decarboxylase in the liver, whereas single administration of thyroxine on the 7th day after thyroidectomy could not bring about such restoration. It seems that thyroxine has no direct role on ascorbic acid metabolism in rats.