GCG and pancreatic insulinoma: The observation that GIP inhibits lipolysis by suppressing glucagon-stimulated cAMP production [769,770] is somewhat unexpected, given that GIP increases cAMP production in a variety of cells, including isolated pancreatic islets [48,636], mouse betaTC-3 cells [168], hamster In11 β-cells [637], rat insulinoma RINm5F cells [545], isolated rat α-cells [732], αTC1-cells [728], HEK293 cells transfected to express GIPR [548], human subcutaneous adipocytes [559] and also isolated rat adipocytes [769] and differentiated 3T3L1 adipocytes [597].