Aims/hypothesis  

Type 2 diabetic patients have been shown to have reduced basal platelet nitric oxide synthase activity, which is a possible contributor to the vascular complications seen in the disease. We investigated platelet nitric oxide generation stimulated by -adrenoceptors and adenylyl cyclase in Type 2 diabetic patients and control subjects.

Methods  

Platelets isolated from blood taken from nine Type 2 diabetic patients and nine healthy control subjects of similar age were treated with isoproterenol 1 µmol/l, forskolin 1 µmol/l or vehicle. Platelet nitric oxide synthase activity was measured by L-[³H]-arginine to L-[³H]-citrulline conversion, cyclic GMP content by radioimmunoassay, and nitric oxide synthase type 3 expression by western blotting.

Results  

Basal platelet nitric oxide synthase activity was lower in diabetic patients than in control subjects (0.01±0.02 pmol L-citrulline/10⁸ platelets, compared with 0.12±0.05; p<0.05), although no corresponding difference was seen in basal platelet cyclic GMP (0.61±0.39 and 0.13±0.22 pmol cyclic GMP/10⁸ platelets respectively; p=0.37). In control subjects isoproterenol 1 µmol/l and forskolin 1 µmol/l increased platelet nitric oxide synthase activity (to 0.27±0.08 and 0.27±0.07 pmol L-citrulline/10⁸ platelets respectively; p<0.05 for each in comparison with basal) and cyclic GMP (to 1.84±0.41 and 1.86±0.48; p<0.05 for each in comparison with basal). This effect was not achieved in diabetic patients. Isoproterenol- and forskolin-stimulated cyclic GMP correlated inversely with plasma glucose and HbA_1c. Platelet nitric oxide synthase type 3 expression was not different in control and diabetic subjects and was not changed by acute exposure of platelets to isoproterenol.

Conclusions/interpretation  

Nitric oxide generation stimulated by -adrenoceptors and adenylyl cyclase is impaired in platelets of people with Type 2 diabetes mellitus, with no corresponding change in nitric oxide synthase type 3 expression. It is possible that this impairment contributes to the thrombotic and atherosclerotic complications of Type 2 diabetes.