The rat GIP receptor (rGIPR) was cloned in 1993 from cDNA libraries of rat cerebral cortex and rat insulinoma RINm5F cells [541] (Figure 1), characterizing GIPR as a seven-transmembrane G protein-coupled receptor (GPCR) of the class B (a.k.a. secretin receptor) family. Here, GIPR is linked to pancreatic insulinoma.