Insulin resistance is a uniform finding in type 2 diabetes, as are abnormalities in the microvascular and macrovascular circulations. These complications are associated with dysfunction of platelets and the neurovascular unit. Platelets are essential for hemostasis, and knowledge of their function is basic to understanding the pathophysiology of vascular disease in diabetes. Intact healthy vascular endothelium is central to the normal functioning of smooth muscle contractility as well as its normal interaction with platelets. What is not clear is the role of hyperglycemia in the functional and organic microvascular deficiencies and platelet hyperactivity in individuals with diabetes. The entire coagulation cascade is dysfunctional in diabetes. Increased levels of fibrinogen and plasminogen activator inhibitor 1 favor both thrombosis and defective dissolution of clots once formed. Platelets in type 2 diabetic individuals adhere to vascular endothelium and aggregate more readily than those in healthy people. Loss of sensitivity to the normal restraints exercised by prostacyclin (PGI 2 ) and nitric oxide (NO) generated by the vascular endothelium presents as the major defect in platelet function. Insulin is a natural antagonist of platelet hyperactivity. It sensitizes the platelet to PGI 2 and enhances endothelial generation of PGI 2 and NO. Thus, the defects in insulin action in diabetes create a milieu of disordered platelet activity conducive to macrovascular and microvascular events.
Diabetes Care 24:1476 -1485, 2001I nsulin resistance (IR) (i.e., resistance to insulin-stimulated glucose uptake) presents in a majority of individuals with type 2 diabetes; it appears to be a common precursor of both diabetes and macrovascular disease (1). IR is a multisystem disorder that is associated with multiple metabolic and cellular alterations. Factors that contribute to IR are genetics, obesity, physical inactivity, and advancing age (2). Metabolic disturbances that commonly occur in patients with IR are atherogenic dyslipidemia, hypertension, glucose intolerance, and a prothrombotic state (1,2).Atherogenic dyslipidemia is characterized by three lipoprotein abnormalities: elevated VLDL, small LDL particles, and decreased HDL cholesterol levels (the lipid triad), also named the atherogenic lipoprotein phenotype (2). This triad is the hallmark of people with diabetes and IR and appears to be an atherogenic phenotype independent of elevated levels of LDL cholesterol (2). As a corollary, most patients with IR have this phenotype even if they are not diabetic, and it may precede the development of diabetes by many years (2).Hypertension, a well-established risk factor for macrovascular events, is also associated with IR. In fact, a direct relationship between plasma insulin concentration and blood pressure has been noted (1). Although the list of multifactorial events that link hypertension and IR is growing (3), currently, the emphasis rests on the role of the endothelial cell.Hypertension is a component of the metabolic synd...