Impairment of glycine absorption by glucose and galactose in man

Abstract

1. In order to investigate a possible competition for intestinal transport between amino acids and monosaccharides in man, iso-osmotic solutions containing (A) 100 m-mole glycine 1.(-1), (B) 100 m-mole glycine and 200 m-mole monosaccharide (glucose or galactose) 1.(-1), and (C) 200 m-mole monosaccharide 1.(-1), were successively perfused into the upper jejunum of twelve African Zambian patients. None had clinical evidence of malnutrition or small-intestinal disease. By using a double-lumen tube and by reference to a non-absorbable marker (polyethylene glycol, 4000), the rates of absorption of these substances have been calculated for a 30 cm jejunal segment.2. The presence of glucose and galactose produced a significant impairment (up to 50%) in the rate of absorption of glycine. There was also a significant decrease in the uptake of both monosaccharides from the solutions in which glycine was also present.3. If this observation also applies to other amino acids it could have a practical value in population groups living on high carbohydrate diets with a marginal concentration of some essential amino acids. It could have special importance when the jejunal mucosa is damaged in severe malnutrition or gastrointestinal infection. This impairment of amino acid uptake may explain the very high incidence of genetically determined lactase-deficiency in Africa.