INS and obesity due to melanocortin 4 receptor deficiency: A recent study found that ex-vivo islet insulin secretion was comparable between WC C57BL/6 J mice and controls with obesity, whereas arterial insulin AUC during a hyperglycemic clamp was significantly reduced, suggesting that a leftward shift in GSIS does not exist in-vivo at least in C57BL/6 J mice [28].