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Tissue levels are decreased by virtually all forms of stress, which also stimulates the biosynthesis of the vitamin in those animals capable of synthesis.
In its metabolism, ascorbic acid is first converted to dehydroascorbate by several enzymes or nonenzymatic processes and can then be reduced back to ascorbic acid in cells (Johnston et al., 2007).
Absorbed vitamin C readily equilibrates with the body pool of the vitamin.
In experimental animals, highest concentrations of vitamin C are found in the pituitary and adrenal glands, and high levels are also found in the liver, spleen, brain and pancreas.
Vitamin C also tends to localize around healing wounds.
Bioavailability of vitamin C in feeds is limited, but apparently 80% to 90% appears to be absorbed (Kallner et al., 1977).
Site of absorption in the guinea pig is in the duodenal and proximal small intestine, whereas the rat showed highest absorption in the ileum (Hornig et al., 1984).
The L-isomer of ascorbic acid is biologically active; the D-isomer is not.
In nature, the reduced form of ascorbic acid may reversibly oxidize to the dehydroxidized form, the dehydroascorbic acid is irreversibly oxidized to the inactive diketogulonic acid.
Vitamin C is a white to yellow-tinged crystalline powder.
It crystallizes out of water as square or oblong crystals (Illus.