Stimulation of CCK and GLP-1 secretion and expression in STC-1 cells by human jejunal contents and in vitro gastrointestinal digests from casein and whey proteins

The present study evaluates casein and whey protein gastrointestinal digests as inducers of CCK and GLP-1 secretion and expression in STC-1 cells. In vitro digests were characterized regarding protein, peptide and free amino acid content. Digests from the intestinal phase containing small size peptides and free amino acids behaved as more potent CCK inducers than digests from the gastric phase. However, GLP-1 release was maximized with casein gastric digests and whey protein intestinal digests. Human jejunal digests from the same substrates showed a comparable response, except for casein jejunal digests which exerted a higher effect than in vitro casein gastrointestinal digests. The gene expression experiments also showed increased CCK and GLP-1 mRNA levels but the differences between the gastric and gastrointestinal phases were not as pronounced as observed by quantifying the secreted hormone. Our results demonstrate that the degree of protein hydrolysis during digestion plays an important role in CCK and GLP-1 secretion.