Deficient platelet-derived nitric oxide and enhanced hemostasis in mice lacking the NOSIII gene

Endothelial nitric oxide synthase (eNOS) has been identified inhuman platel ets. Although platelet-derived nitric oxide (NO) has been shown to inhibit platelet recruitment in vitro, its role in the regulation of the hemostatic ;response in vivo has not been characterized. To define the role of platel et-derived NO in vivo, we studied mice that lacked a functional eNOS gene ( NOSIII). Surface P-selectin expression in platelets from eNOS-deficient mic e was not significantly altered; however, bleeding times were markedly decr eased in eNOS-deficient versus wild-type mice (77.2+/-3 versus 133.4+/-3 se conds, P<0.00005). To determine the contribution of endothelium- versus pla telet-derived NO to the bleeding time, isolated platelets from either eNOS- deficient or wild-type mice were transfused into a thrombocytopenic eNOS-de ficient mouse and the bleeding time was measured. The bleeding times in mic e transfused with eNOS-deficient platelets were significantly decreased com pared with mice transfused with wild-type platelets (Delta bleeding time, - 24.6 +/- 9.1 and -3.4+/-5.3 seconds, respectively; P<0.04). Platelet recrui tment was studied by measuring serotonin release from a second recruitable population of platelets that were added to stimulated platelets at the peak of NO production. There was 40.3+/-3.7% and 52.0+/-2.1% serotonin release for platelets added to wild-type or eNOS-deficient platelets, respectively (P<0.05). In summary, mice that lacked eNOS had markedly decreased bleeding times even after endothelial NO production was controlled. These data sugg est that the lack of platelet-derived NO alters in vivo hemostatic response by increasing platelet recruitment. Thus, these data support a role for pl atelet-derived NO production in the regulation of hemostasis.