Effect of fermentable carbohydrates on volatile fatty acids, ammonia and mineral absorption in the rat caecum.

The effects of poorly digested carbohydrates in the small intestine on caecal digestion and absorption have been studied in the rat. Even in diets lacking these carbohydrates, there was a noticeable production of volatile fatty acids (VFA) in the caecum. Except for cellulose, the carbohydrates (bran, pectin, guar-gum, crude potato-starch, lactose, lactulose) favoured considerable development of the caecum and enhanced the quantities of VFA present there. On reaching the caecum, they increased ammonia absorption as a result of a higher uptake of blood urea, even if a greater part of the urea nitrogen was used in bacterial protein synthesis. Arteriovenous differences in the caecum showed a considerable absorption of various electrolytes. VFA absorption seemed to be accompanied by a release of Cl- into the caecal contents and by absorption of the main cations, Na+ being absorbed along an unfavourable gradient between the plasma and the caecal contents.