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...

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Treatment of platelets with a prostacyclin analogue, iloprost, decreased the cholera-toxin-induced ADP-ribosylation of membrane-bound Gs alpha (alpha-subunit of G-protein that stimulates adenylate cyclase; 42 kDa protein) and a cytosolic substrate (44 kDa protein) [Molina y Vedia, Reep & Lapetina (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 5899-5902]. This decrease is apparently not correlated with a significant change in the quantity of membrane Gs alpha, as detected by two Gs alpha-specific antisera. This finding contrasts with the suggestion in a previous report [Edwards, MacDermot & Wilkins (1987) Br. J. Pharmacol. 90, 501-510], indicating that iloprost caused a loss of Gs alpha from the membrane. Our evidence points to a modification in the ability of the 42 kDa protein to be ADP-ribosylated by cholera toxin. This modification of Gs alpha might be related to its ADP-ribosylation by endogenous ADP-ribosyltransferase activity. Here we present evidence showing that Gs alpha was ADP-ribosylated in platelets that had been electropermeabilized and incubated with [alpha-32P]NAD+. This endogenous ADP-ribosylation of Gs alpha is inhibited by nicotinamide and stimulated by iloprost.

The activity of phosphatidylinositol (PI) 3-kinase was examined in murine bone marrow-derived macrophages (BMM) stimulated with the haematopoietic growth factors colony stimulating factor-1 (CSF-1) and granulocyte/macrophage-CSF (GM-CSF). PI 3-kinase was immunoprecipitated from cell lysates using anti-phosphotyrosine antibody or an antibody directed against the 85K subunit of PI 3-kinase, and the activity assayed by the phosphorylation of PI in the presence of [gamma 32P]-ATP. The results demonstrate that CSF-1 increases the activity of PI 3-kinase, as compared to the non-stimulated control, in murine macrophages. Maximum activity was seen after 10 min of stimulation with CSF-1 at 3000-5000 U/ml. The dose-response of CSF-1 is consistent with other biochemical effects of CSF-1 seen in the BMM. GM-CSF also stimulated PI 3-kinase activity although to a lesser extent than CSF-1, correlating well with their degree of mitogenic activity on the BMM. Non-mitogenic macrophage activating agents, such as the phorbol myristate acetate, lipopolysaccharide, concanavalin A and formyl-methionyl-leucyl-phenylalanine, did not significantly increase the PI 3-kinase activity. Furthermore, CSF-1 failed to stimulate PI 3-kinase activity in resident peritoneal macrophages, a population of macrophages with poor proliferative capacity. These results suggest that the PI 3-kinase activity may be involved in the haemopoietic growth factor signalling pathways regulating macrophage growth.