Abstract
This study was undertaken to investigate the response of sucrase (SA), alkaline phosphatase (ALP), and leucine aminopeptidase (LAP) activities localized in the brush border membrane of the small intestine to ingested nutrients. In rats previously meal-fed on carbohydrate-free diets, the maximal increase in SA activity after the administration of a 18 % casein and high sucrose diet (HSD) occurred 24 hr after the beginning of the 12-hr period of HSD-feeding, but ALP and LAP activities reached the maximal levels 12hr after the HSD administration and then rapidly declined. These changes in three enzyme activities were similar to those after HSD-feeding following a 2-day fast, but those were not observed after giving a carbohydrate-free and high fat diet. The increases in these enzyme activities after giving HSD were not observed entirely after giving HSD containing 0.5% concanavalin A, which was undigestible and preferentially bound mitotically active cells of the small intestine. From these findings, it can be suggested that the adaptive response of these enzyme activities to ingested nutrients, as sucrose and casein, was produced on the luminal surface of the small intestine, especially on the immature cells.
