Intestinal amino acid transport in mice is modulated by diabetes and diet

Diet is the cornerstone of diabetes management, but nutritional interventions in diabetes are still being developed; hence, it is important to understand the effects of diet on nutrient metabolism. Dietary sugars stimulate intestinal sugar absorption in diabetic mice, but the effect of dietary protein on amino acid absorption in diabetes is unknown. We fed streptozotocin-diabetic (>60 d diabetic) and nondiabetic mice high protein (70% casein) or low protein (15% casein) diets designed to elicit adaptation in amino acid uptake by the small intestine. A high protein diet significantly enhanced uptake per milligram of small intestine of the nonessential amino acids proline and aspartate in both diabetic and nondiabetic mice. Uptake per milligram of small intestine of the essential amino acids leucine and lysine and of the nonessential amino acid alanine which shares transporters with essential amino acids was independent of dietary protein. There was no effect of diabetes on uptake per milligram of any amino acid studied. Because weight per centimeter was greater in diabetic mice, uptake per centimeter of all amino acids tended to be greater in diabetics. Specific activity of alkaline phosphatase in the proximal and distal jejunum was independent of diabetes but varied with dietary protein. Changes in levels of dietary protein induce reversible adaptation of the intestinal uptake rate of nonessential but not of essential amino acids, an adaptive pattern typical of nondiabetics and apparently maintained in diabetics as well.