The term incretin describes a hormone that is secretedfrom the gut that enhances the release of insulin inresponse to a meal. It had been known for many decadesthat oral glucose produced a greater insulin responsethan intravenous glucose, and in the 1960s MacIntyredemonstrated that intestinal factors were responsible forthis effect (described by the term enteroinsular axis).1The isolation of GIP (glucose-dependent insulinotropicpolypeptide or gastric inhibitory peptide) in 1970was followed in the 1980s by the recognition of GLP-1(glucagon-like peptide-1) a product of proglucagon, analoguesof which have been developed for treating type2 diabetes. GLP-1 is derived from L cells in the distalgut by cleavage of pre-proglucagon by prohormoneconvertase enzymes expressed within the gut.
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