Ascorbic acid renal transport

Sublethal effects in birds are similar to those in other species and include growth retardation, anemia, renal effects, and testicular damage (Hammons et al. 1978 Di Giulio et al. 1984 Blus et al. 1993). However, harmful damage effects were observed at higher concentrations when compared to aquatic biota. For example, Japanese quail (Coturnix japonica) fed 75 mg Cd/kg diet developed bone marrow hypoplasia, anemia, and hypertrophy of both heart ventricles at 6 weeks (Richardson et al. 1974). In zinc-deficient diets, effects were especially pronounced and included all of the signs mentioned plus testicular hypoplasia. A similar pattern was evident in cadmium-stressed quail on an iron-deficient diet. In all tests, 1% ascorbic acid in the diet prevented cadmium-induced effects in Japanese quail (Richardson et al. 1974). In studies with Japanese quail at environmentally relevant concentrations of 10 pg Cd/kg B W daily (for 4 days, administered per os), absorbed cadmium was transported in blood in a form that enhanced deposition in the kidney less than 0.7% of the total administered dose was recovered from liver plus kidneys plus duodenum (Scheuhammer 1988). 

There must also be a second mechanism of ascorbic acid transport through certain specialized cells, difierent from the diffusion of dehydro-ascorbic acid followed by intracellular reduction. There are no indications that dehydroascorbic acid is involved in the renal tubular absorption of ascorbic acid, and, contrary to earlier conclusions, it appears that the concentration of ascorbic acid into the aqueous humors of the eye occurs in the form of ascorbic acid itself. 

Bianchi, J. Rose, R. C. 1985. Transport of L-ascorbic acid and dehydro-L-ascorbic acid across renal cortical basolateral membrane vesicles. Biochim. Biophys. Acta 820(2) 265-273. Bode, A. M. Yavarow, C. R. 1993. Enzymatic basis for altered ascorbic acid and dehydro-ascorbic acid levels in diabetes. Biochem. Biophys. Res. Commun. 191 1347-1353. Biondi, C. Pavan, B. Dalpiaz, A. Medici, S. Lunghi, L. Vesce, F. 2007. Expression and characterization of vitamin C transporter in the human trophoblast cell line HTR-8/ SVneo Effect of steroids, flavonoids, and NSAIDs. Mol. Hum. Reprod 13(1) 77-83. Boyer, J. C. Campbell, C. E. Sigurdson, W. J. Kuo, S. M. 2005. Polarized localization of vitamin C transporters, SVCTl and SVCT2, in epithelial cells. Biochem. Biophys. Res. Commun. 334 150-156. 

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