Relationship of thrombohemorrhagic complications to endothelial cell function in patients with chronic myeloproliferative disorders.

Thrombotic and hemorrhagic disorders are common complications of the myeloproliferative disorders. Endothelial cells release both procoagulant and profibrinolytic factors, which may contribute to these hemorrhagic or thrombotic complications. The pre- and postvenous stasis levels of the procoagulant and profibrinolytic factors produced by endothelial cells were correlated with the occurrence of complications in polycythemia rubra vera (PRV) patients (n = 29) and essential thrombocythemia (ET) patients (n = 17) compared with normal patients (n = 17). Tissue plasminogen activator (tPA) activity, plasminogen activator inhibitor (PAI) activity, von Willebrand's factor (vWF) activity and antigen (vWF:Ag), and factor VIII activity were measured. The resting tPA activity was significantly higher in the two disease groups compared with normal controls, but no difference between the levels of tPA and either complication within the disease groups was observed. Significantly elevated tPA following venous stasis was observed in the patients of both disease groups who had bleeding complications. Significant decreases, compared with the normal group, in both resting and postvenous stasis levels of PAI were observed in the disease groups regardless of complication history. The subjects from both disease groups with thrombotic complications had significantly elevated resting vWF and both resting and postvenous stasis vWF:Ag levels compared with normal controls. The endothelial cell is likely to be responding to abnormal hemostasis rather than being primarily involved in the genesis of a hyper- or hypocoaguable state.