Abstract
To investigate the mechanism of oral fat-stimulated secretion of the two most potent incretin candidates, gastric inhibitory polypeptide (GIP) and truncated glucagon-like peptide-1 (tGLP-1), we studied changes in these peptides after fat ingestion using long-chain triglyceride (LCT) or medium chain triglyceride (MCT) in man.25g LCT was given orally to nine healthy volunteers and 25g MCT was given orally to six healthy volunteers.After LCT ingestion plasma levels of GIP peaked at 60 min and glucagon-like immunoreactivity (GLI) at 30 min, and both remained high up to 120 min, whereas plasma glucose, insulin and glucagon levels were unchanged.Plasma levels of GLP-1 NT, measured with antiserum R1043 (N-terminus directed), increased markedly.Estimated values of tGLP-1, obtained by the subtraction of GLP-1 NT values from those of GLP-1 CT, increased markedly within 30 min and declined rapidly within 60 min.However, after MCT ingestion, plasma levels of all of the above parameters remained unchanged.Plasma levels of triglyceride and chylomicron were increased by LCT ingestion, but only plasma very low density lipoproteins were increased by MCT ingestion.The results suggest that the absorption process, especially chylomicron formation, is an important determinant of fat stimulated tGLP-1 release, as in GIP release.
