['The purpose of this study was to examine vasomotor responses mediated by platelets from patients with diabetes mellitus.', 'Diabetes mellitus is associated with increased cardiovascular morbidity and mortality, which in part may be due to a variety of abnormalities reported in diabetic platelets. However, the effects of diabetic platelets on vasomotor tone have not been characterized.', 'We compared platelet-mediated vasodilation elicited by platelets isolated from 30 healthy volunteers and 29 patients with diabetes mellitus as they were perfused through a preconstricted normal rabbit carotid artery.', 'Platelets from the diabetic patients mediated an impaired dilatory response in comparison with normal platelets: 2.7 +/- 2% versus 15.8 +/- 3.4% (p < 0.001) and 4.1 +/- 2.7% versus 32.7 +/- 3.3% (p < 0.001) (mean +/- SEM) increase in vessel diameter, for 5 X 10(7) and 1 X 10(8) platelets per milliliter perfused, respectively. The degree of impairment was similar for type I (insulin-dependent) and type II (non-insulin-dependent) diabetes mellitus. Normal platelets incubated in high D-glucose concentrations lost their ability to mediate dilation in a concentration-dependent and time-dependent manner. This was not true for incubation of normal platelets in high concentrations of L-glucose or insulin. However, there was not a significant correlation between glucose control in the diabetic patients and the ability of their platelets to mediate vasodilation.'] Do platelets from patients with diabetes mellitus have impaired ability to mediate vasodilation?