Nitric oxide generation mediated by beta-adrenoceptors is impaired in platelets from patients with Type 2 diabetes mellitus.
OBJECTIVE
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 beta-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 micro mol/l, forskolin 1 micro mol/l or vehicle. Platelet nitric oxide synthase activity was measured by L-[(3)H]-arginine to L-[(3)H]-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/10(8) 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/10(8) platelets respectively; p=0.37). In control subjects isoproterenol 1 micro mol/l and forskolin 1 micro mol/l increased platelet nitric oxide synthase activity (to 0.27+/-0.08 and 0.27+/-0.07 pmol L-citrulline/10(8) 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
Nitric oxide generation stimulated by beta-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.
GKT School of Medicine (Cardiovascular Division), King's College London, London, UK. lindsay.queen@kcl.ac.uk
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Queen
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Ji
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Goubareva
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Ferro
D000806:Angiotensin-Converting Enzyme Inhibitors / Q000627:therapeutic use; D001786:Blood Glucose / Q000378:metabolism; D001792:Blood Platelets / Q000502:physiology*; D002784:Cholesterol / Q000097:blood; D006152:Cyclic GMP / Q000097:blood; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000188:drug therapy; D005260:Female; D005905:Glyburide / Q000627:therapeutic use; D006442:Glycated Hemoglobin / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use; D008297:Male; D008687:Metformin / Q000627:therapeutic use; D008875:Middle Aged; D009569:Nitric Oxide / Q000097:blood*; D019001:Nitric Oxide Synthase / Q000097:blood; D011943:Receptors, Adrenergic, beta / Q000097:blood*; D012044:Regression Analysis; D014280:Triglycerides / Q000097:blood
D000806:Angiotensin-Converting Enzyme Inhibitors; D001786:Blood Glucose; D002784:Cholesterol; D006152:Cyclic GMP; D005905:Glyburide; D006442:Glycated Hemoglobin; D007004:Hypoglycemic Agents; D008687:Metformin; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D011943:Receptors, Adrenergic, beta; D014280:Triglycerides