Contents Enhanced glucagon-like peptide-1 secretion in a patient with glucagonoma: Implications for glucagon-like peptide-1 secretion from pancreatic α cells in vivo. Objective. Glucagon-like peptide-1(GLP-1) is secreted from gastrointestinal endocrine cells, and enhances insulin secretion from pancreatic β cells glucose-dependently. Recent studies suggest that GLP-1 is also secreted from pancreatic α cells, and may act on β cells in a paracrine fashion. However, it is not known whether GLP-1 is secreted from human pancreatic α cells in vivo. Research Design and Methods 53 year-old man, who had been diagnosed as multiple endocrine neoplasia type 1, underwent partial pancretectomy for glucagonoma and his GLP-1 secretion from the pancreas was evaluated by three approaches: 1) meal tolerance tests(480kcal, carbohydrate: protein: fat = 2.8:1:1) before and after the operation, 2) selective arterial injection of calcium gluconate, a novel technique to evaluate pancreatic GLP-1 secretion in vivo before operation, and 3) immunohistochemical analysis of the surgically resected pancreatic tissues. Results We found that 1) fasting GLP-1 level was much higher than control and the elevated fasting and postprandial levels of GLP-1 were near-normalized by the operation, 2) GLP-1 secretion in vivo from the pancreas was enhanced by the injection of calcium gluconate, and 3) both tumors and normal islets were positive for GLP-1 immunohistochemically. Conclusions Our analysis of this case of glucagonoma supports the notion that GLP-1 may be secreted from α cells in healthy human.