Sex differences in platelet adherence to subendothelium: relationship to platelet function tests and hematologic variables.

Men have significantly more atherosclerotic disease than women. Platelet-mediated thrombosis plays a role in the initiation of myocardial infarction and stroke. Citrated whole blood from male and female donors was perfused through an annular system over everted human umbilical artery segments. Comparisons were made between platelet adherence and thrombus formation on subendothelium, platelet aggregation in citrated whole blood, hematologic variables, and the bleeding time. Platelet spreading and adherence were approximately 22% greater with male blood (P < 0.001), whereas thrombus formation on subendothelium and collagen- and arachidonic acid-induced platelet aggregation did not show sex-related differences. Platelet aggregation with adenosine diphosphate was greater in women, related to their lower hematocrit values. By contrast, in women hematocrit values showed a slight but significant positive correlation with platelet adherence on subendothelium. Fibrinogen was significantly correlated with collagen- and adenosine-diphosphate-induced platelet aggregation and with platelet adherence, spreading, and thrombus formation on subendothelium. The mean bleeding time was slightly longer in women than in men (P = 0.118). Platelet aggregation was not associated with the bleeding time except for collagen-induced platelet aggregation in males; the latter was significantly correlated with platelet adherence and spreading in both sexes, while arachidonic acid-induced platelet aggregation predicted platelet adherence and spreading in males. Male blood shows enhanced primary hemostatic activity; this may predispose men to atherosclerosis.

Whole-blood platelet aggregation predicts in vitro and in vivo primary hemostatic function in the elderly.

Increased platelet aggregation is associated with higher coronary artery disease mortality. Enhanced platelet aggregation in platelet-rich plasma has also been described in the elderly. To define age-related changes in primary hemostasis, we studied 37 elderly and 31 young blood donors. There were no significant age-related differences in whole-blood platelet aggregation, platelet adherence and thrombus formation on human umbilical artery segments, or bleeding time. Plasma fibrinogen was significantly higher in elderly men and women, whereas activated factor VII was elevated only in elderly women. Collagen-induced platelet aggregation was significantly correlated with platelet adherence to the subendothelium in elderly (r = .488, P = .002) but not in young donors. Accordingly, collagen-induced platelet aggregation showed a significant inverse correlation with bleeding time only in the elderly (r = -.401, P = .014). Arachidonic acid-induced platelet aggregation was significantly associated with platelet adherence to the subendothelium (r = .658, P = .003) and bleeding time (r = -.540, P = .021) only in elderly men. In young donors, ADP-induced platelet aggregation was significantly correlated with platelet adherence to the thrombogenic adventitial surface (r = .395, P = .031); in the elderly this association only approached significance (r = .315, P = .058). Whole-blood platelet aggregation in response to collagen and arachidonic acid may be more useful in predicting primary hemostatic function in the elderly than in the young. Furthermore, in the elderly, the correlation between platelet aggregation in whole blood and platelet-arterial wall interactions in vitro and in vivo may contribute to the ability of this test to predict coronary risk.