Effect of feeding a high protein diet on amino acid uptake into rat intestinal brush border membrane vesicles

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Abstract
Uptake of the neutral amino acidl-leucine into isolated rat intestinal brush border membrane (=BBM) vesicles and into a jejunal mucosa preparation as affected by the protein content of the diet was investigated. Adult rats fed either a high carbohydrate (HC) diet (11% protein) or a high protein (HP) diet (77% protein) for several weeks were used for the experiments. The time course ofl-leucine uptake into BBM vesicles prepared from the small intestine of HC-or HP-rats was studied under conditions of an inwardly directed Na+-gradient and under Na+-equilibrium conditions. Furthermore, in one series of experiments the Na+-equilibrium was replaced by a K+-equilibrium. l-leucine uptake under Na+-gradient conditions displayed the overshoot phenomenon typically associated with Na+-gradient-dependent active transport processes in BBM vesicles and the overshoot in group HP exceeded that in group HC significantly. Under both Na+-and K+-equilibrium conditionsl-leucine uptake into the BBM-vesicles also was faster in group HP. Finallyl-leucine uptake into jejunal mucosa in group HP exceeded that in group HC, too. The results therefore indicate that Na+-dependent and Na+-independent transport of neutral amino acids across the intestinal brush border membrane adapts to the dietary protein level.

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