INS and obesity due to melanocortin 4 receptor deficiency: In addition to confirming a significant insulin resistance in the conduit artery and in the skeletal and cardiac muscle microvasculature associated with obesity, the study convincingly demonstrated that the vasodilatory action of GLP-1 was blunted in the conduit artery but preserved in the skeletal and cardiac muscle microvasculature, as evaluated by contrast-enhanced echocardiography [221].