Background & Aims: Dietary protein deficiency results in diminished capacity of the pancreas to secrete enzymes needed for macronutrient digestion. Previous work has suggested that modulation of the mammalian target of rapamycin (mTOR) pathway by the hormone cholecystokinin (CCK) plays an important role in normal digestive enzyme synthesis after feeding. The purpose of this study was to elucidate the role of mTOR in protein deficiency-induced pancreatic dysfunction. Methods: Wild-type and CCK-null mice were fed protein-deficient chow for 4 days and then allowed to recover on control chow in the presence or absence of the mTOR inhibitor rapamycin. Results: The size and secretory capacity of the pancreas rapidly decreased after feeding protein-deficient chow. Refeeding protein-replete chow reversed these changes in both wild-type and CCK-null mice. Changes in the size of the pancreas were paralleled by changes in the content and secretion of digestive enzymes, as well as the phosphorylation of downstream targets of mTOR. Administration of the mTOR inhibitor rapamycin decreased regrowth of the pancreas but did not affect digestive enzyme content or secretory capacity. Conclusions: These studies demonstrate that dietary protein modulates pancreatic growth, but not digestive enzyme synthesis, via CCK-independent activation of the mTOR pathway.
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