To our surprise, although AVP (100 nM) stimulated similar level of glucose-dependent insulin secretion from freshly isolated islets as GLP-1 (Fig. 1D), it failed to induce insulin release from INS-1E (rat insulinoma) or MIN6 (mouse insulinoma), two well-documented cell lines to study insulin secretion and β cell functions, while GLP-1 displayed significant stimulatory effect (Fig. 1E and F). Here, GCG is linked to pancreatic insulinoma.