Summary of Somatostatin
A 45-year-old man comes to the clinic because of a recent weight loss of 4.5-kg (9.9-lb) and fatty stools. He has a history of diabetes mellitus and gallstones. Laboratory studies show decreased concentrations of pepsinogen, amylase, lipase, insulin, and glucagon. A CT scan shows a mass in the pancreas, Based on this patient's symptoms, which of the following substances might be secreted by this pancreatic tumor?