GIP and pancreatic insulinoma: Following the demonstration by Daniel Drucker that GLP-1 autonomously stimulates insulin secretion in rat islet insulinoma “RIN” 1046-38 cells [78], Bernhard Kreymann from Steve Bloom's laboratory then showed that physiological concentrations of GLP-1(7-36)NH2 enhances glucose-stimulated insulin secretion in humans [79], hence establishing GLP-1 as the second incretin hormone (Figure 1).