Glucagon-like peptide-1 (GLP-1) is a neuropeptide and an incretin derived from the transcription product of the proglucagon gene.he known peripheral functions of GLP-1 include: 1  increases insulin secretion from the pancreas in a glucose-dependent manner. 2  increases insulin-sensitivity in both alpha cells and beta cells. 3  increases beta cells mass and insulin expression, PTM, and secretion.