The absorption and metabolism of vitamin C and galactose by the small intestine
The absorption and metabolism of vitamin C by intestinal tissue was investigated using everted sacs from guinea pig small intestine. The two physiologically active forms of the vitamin, ascorbic acid and dehydroascorbic acid, were studied and it was concluded that the former is.translocated by a simple diffusion mechanism, in the jejunal region only, and the latter is transported across the small intestine by a facilitated translocation mechanism. Neither ascorbic acid nor dehydroascorbic acid was found to be metabolised by intestinal tissue.Galactose absorption was studied using everted intestinal sacs from rat small intestine and metabolism of the sugar by using everted sacs and sheets of isolated, intact, columnar absorptive cells. Galactose translocation was found to be Na+ dependent active transport, located in the jejunal region, and no intestinal metabolism of galactose was observed.The activities of the Leloir pathway enzymes for galactose metabolism were measured in homogenates of isolated columnar absorptive cells from rat jejunum. Galactokinase was located solely in a "mitochondrial fraction", and galactose-l-phosphate uridyl transferase and UDP galactose-4-epimerase predominantly in a "cdcrosomal fraction." Homogenates of isolated columnar absorptive cells from rat jejunum metabolised galactose, but the metabolic fate of the sugar is unknown.3Deprivation of food for 72 hours enhanced the activities of the Leloir pathway enzymes. Animals fed after the fasting regime did not have elevated intestinal activities of these enzymes.It was observed that the oxygen consumption rates of the isolated columnar. absorptive cells from rat jejunum were dependent on the strain and animal house environments of the rats. The common factor would appear to be a decrease in .respiration rate with. increasing excitability of the rat on handling prior to the experiment. This was probably triggered by adrenalin release.