In another study, metoprolol use in patients with type 2 diabetes mellitus was shown to be associated with a significant reduction in insulin-stimulated endothelial function where as this function was preserved with carvedilol use[12] One proposed mechanism for this was that selective β1 BB's such as atenolol and metoprolol may cause vasoconstriction, decreased peripheral blood flow and may exacerbate insulin resistance [13], whereas the α-adrenergic blocking effect of carvedilol may allow greater peripheral blood flow and hence increased utilization of glucose. This evidence concerns the gene INS and type 2 diabetes mellitus.