Effects of a high-protein, low-carbohydrate diet on degradation of sucrase-isomaltase in rat jejunoileum.

During the degradation of intestinal sucrase-isomaltase by pancreatic proteinases, degradation of sucrase-active site precedes that of the isomaltase-active site in rats. In the present paper, we demonstrate that the extent of degradation of sucrase-isomaltase is altered by dietary manipulation in vivo. Adult rats were starved for 24 h and received either a standard diet (20 cal% protein, 55% carbohydrate) or an isocaloric high-protein, low-carbohydrate diet (70 cal% protein, 5% carbohydrate). Animals were killed 15 h after the refeeding. In rats fed a high-protein, low-carbohydrate diet, luminal trypsin activity was three times higher than controls, and sucrase activity in proximal ileum was significantly lower (P less than 0.001) than controls, whereas isomaltase activity was similar in both groups. In proximal jejunum, luminal trypsin activity was remarkably lower (P less than 0.01) than in proximal ileum in both groups; sucrase and isomaltase activity was similar in both groups. Crossed immunoelectrophoresis demonstrated that a degradation product of sucrase-isomaltase, i.e., isomaltase monomer, was present in a larger amount in rats fed a high-protein, low-carbohydrate diet. In rats with bypassed pancreatic ducts, the amount of this degradation product was decreased and effect of a high-protein, low-carbohydrate diet was abolished. Experiments with a sequential isolation of epithelial cells of proximal ileum revealed that sucrase activity was decreased along the entire height of the villus in animals fed a high-protein, low-carbohydrate diet.(ABSTRACT TRUNCATED AT 250 WORDS)