Gastrointestinal oxalate absorption

Morozumi, M., Flossain, R. Z., Yamakawa, K., Hokama, S., Nishijima, S., Oshiro, Y., Uchida, A., Sugaya, K., and Ogawa, Y. (2006). Gastrointestinal oxalic acid absorption in calcium-treated rats. Urol. Res. 34,168-172. 

If the drug is insoluble in water, suspensions have to be administered. In such cases vehicles like sesame oil, hydroxy-methyl-cellulose or hydroxy-ethyl-cellulose can be used. The selection of the vehicle is a critical issue because of inherent toxicity of the vehicle used frequently for kinetic and metabolism studies (e.g. vehicles which form metabolically oxalic acid). Natural oils such as sesame or com oil can be used. However, it should be checked whether the use of oily vehicles alters the gastrointestinal absorption due to their laxative properties and whether oily vehicles can cause oil granulomas (reaction to oily vehicles in the reticulo-endothelial system) in case of parenteral administration. 

The nature of the anion making up the Cr(III) salt, as well as the gastrointestinal tract contents and the nutritional status of the animal, are important determinants of efficiency of absorption from the gastrointestinal tract. For example, oxalates are better absorbed than phytates (Chen et al. 1973). There is a suggestion that biologically active complexes of Cr(III) are even better absorbed, perhaps to the extent of 10%-25% (Mertz and Roginski 1971). Zinc status also influences chromium absorption (Hahn and Evans 1975). Both Cr(III) and Cr(VI) salts are better absorbed in the fasting than in the fed state (Mackenzie et al. 1959). 

Absorption of calcium is influenced by many factors. The maintenance of normal gastric acidity facilitates absorption, and vitamin D enhances it. Absorption is increased by protein, lactose, and citrates in the diet. Absorption is decreased by the presence of phytates (in cereals), oxalates, and fatty acids, since in each instance insoluble calcium salts are formed. The ratio of calcium to phosphorus in the diet influences absorption. Calcium enters the gastrointestinal tract not only in food but as a component of digestive secretions as much as 0.3 to 0.8 g. daily may be secreted into the gastrointestinal tract. Reabsorption of this calcium is influenced by the factors just enumerated. 

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