Reduced membrane fluidity in platelets from diabetic patients.
 Platelets from diabetic patients are hypersensitive to agonists in vitro.
 Membrane fluidity modulates cell function, and reduced membrane fluidity in cholesterol-enriched platelets is associated with platelet hypersensitivity to agonists, including thrombin.
 Decreased membrane fluidity of these platelets is attributed to an increased cholesterol-phospholipid molar ratio in platelet membranes.
 We examined the response of platelets from diabetic subjects to thrombin, platelet membrane fluidity, and platelet cholesterol-phospholipid molar ratio.
 Twelve poorly controlled diabetic subjects were compared with 12 age- and sex-matched control subjects.
 In response to a low concentration of thrombin, mean values for release of [14C]serotonin from washed prelabeled platelets were not significantly different between diabetic and control subjects, but in 8 of 12 diabetic subjects, the release response was greater than in their paired control subjects.
 Mean steady-state fluorescence polarization values in 1,6-diphenyl-1,3,5-hexatriene-labeled platelets prepared from diabetic subjects were significantly greater than in control subjects; this indicates a decreased membrane fluidity in platelets from diabetic subjects.
 Total or very-low-density (VLDL), low-density (LDL), or high-density (HDL2, HDL3) lipoprotein cholesterol concentrations in plasma were not significantly different between groups; however, the ratio of VLDL + LDL to HDL2 + HDL3 was significantly greater in diabetic than in control subjects.
 There was no difference in the total platelet cholesterol-phospholipid molar ratio between groups.
