INS and metabolic syndrome: On the contrary, MetS was associated with a significant reduction in the endothelium-dependent relaxation measured as the vascular response of aortic rings to accumulative concentrations of Ach (p < 0.05; Figure 8B) or the vascular response of aorta segments to a single dose of insulin (p < 0.01; Figure 8D), indicating the presence of endothelial dysfunction.