Tissue ascorbic acid

Yew, M.S. (1983). Effect of streptozotocin diabetes on tissue ascorbic acid and dehydroascorbic acid. Horm. Metab. Res. 15, 158. 

The turnover rates of ascorbic acid from tissues (afflux Tti) were larger than the afflux (see Table III, column headed "Tn/Ti/ ), suggesting either that the distribution equilibrium between labeled ascorbic acid and available tissue ascorbic acid has not been reached, or that part of the compartmental pool of ascorbic acid cannot be exchanged. Therefore, formal calculation of the total turnover of ascorbic acid using tissue data results in a turnover somewhat larger than that calculated using plasma data (mean value 12.5-8 mg/d). When calculated from the food intake, the turnover is 16 it 3 mg/d therefore, one must assume that the bioavailability of ascorbic acid present in the diet is not 100%. Studies on the absorption of ascorbic acid in humans have demonstrated... 

Biochemical changes in scurvy not associated with discrete enzymes have been reported. The ratio of RNA to DNA increased in spleen and adrenals (G6). The DNA content of a fibrosarcoma was decreased by scurvy, and glucoascorbic acid given to lower the tissue ascorbic acid levels in rats decreased the DNA in rat carcinoma (S21). Dinning et al. (D15) expected defects in the reactions where folic acid participates. 

C14. Collins, M., and Elvehjem, C. A., Ascorbic acid requirement of the guinea pig using growth and tissue ascorbic acid concentrations as criteria. /. Nutrition 64, 503-511 (1958). 

The influence of flavonoids on the accumulation and metabolism of tissue ascorbic acid. 

DIETARY FLAVONOIDS AND TISSUE ASCORBIC ACID Studies with guinea-pigs... 

Metabolic sparing of ascorbic acid by flavonoids. The fourth possible mechanism for the flavonoid-induced increases in tissue ascorbic acid is that flavonoids, by taking over some of the biological functions of the acid, thereby reduce the metabolic demand for the vitamin and permit its increased accumulation in the tissues. The inability of flavonoids to prolong the life of scorbutic guinea-pigs [43,46] implies that if substitution occurs then it must be in an area other than that normally associated with the development of scurvy — namely, the defective hydroxylation of the collagen molecule precursor. A possible corollary of this is that ascorbic acid is a multifunctional vitamin, with functional substitution by flavonoids possible only in certain metabolic areas. Such partial substitution is not unknown in nutrition the partial replacement in animals of the vitamin E function of tocopherols by antioxidants is a case in point. 

Vitamin C Vitamin C activity resides in two naturally occurring compounds ascorbic acid and its oxidation product, dehydroascorbic acid. In human tissues ascorbic acid predominates. Ascorbic acid is labile in most samples, oxidizing to dehydroascorbic acid and then degrading to 2,3-diketogluconic acid. Various reagents can be used to prevent this oxidation in plasma or whole blood samples. Extraction with 5% metaphosphoric or trichloroacetic acid is the usual initial preparation. Only ascorbic acid may be detected by UV spectrophotometry at 245-265 nm, the absorption maxima of dehydroascorbic acid being 210 nm. A similar problem exists with electrochemical detection where ascorbic acid oxidizes at +0.7V with carbon electrodes. Fluorescent derivatives may be formed with 2-4-din-itrophenylhydrazine or o-phenyldiamine. These derivatives can be assayed by reversed-phase HPLC. 

Dorr, P.E. and Nockels, C.F. (1971) Effects of aging and dietary ascorbic acid on tissue ascorbic acid in the domestic hen. Poult. Sci. 50, 1375-1382. 

In corneal tissue, ascorbic acid was able to inhibit the activity of lipoxygenase and reduce the production of 12-hydroxyeicosatetraeroic acid, the major lipoxygenase product produced by the cornea (Williams and Paterson, 1986). 

Mcllwain, H., Thomas, J., and Bell, J. L., 1956, The composition of isolated cerebral tissues Ascorbic acid and coenzymes, Biochem. J. 64 332-335. 

The eye is one of several organs in the body that maintains a high concentration of ascorbic acid. As in other tissues, ascorbic acid is thought to function as an antioxidant, as a factor involved in collagen synthesis, as a redox coupler involved... 

In liver tissue, ascorbic acid has been found to be stable without any stabilizing agent for many hours at +5°C (69). This is possibly due to the high levels of endogenous low-molecular-weight reductants, such as glutathione, which are highly concentrated in liver. 

Combined UV and electrochemical detection was used for determining ascorbic acid and DHA in small animal and brain tissues. Ascorbic acid was detected amperometrically and DHA at the wavelength of 215 nm in a single run. However, quantitative measurement of DHA might be difficult with this method, because of several interfering compounds absorbing at this wavelength (86). 

Ascorbic acid deficiency is thought to predispose to aspirin-induced gastrointestinal haemorrhage (see above), and aspirin depletes tissue ascorbic acid stores (98). 

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