Hassan S, Sainz IM, Khan MM, Bradford HN, Isordia-Salas I, Kashem SW, Sartor RB, Colman RW. Antithrombotic activity of kininogen is mediated by inhibitory effects of domain 3 during arterial injury in vivo. Am J Physiol Heart Circ Physiol 292: H2959 -H2965, 2007. First published February 9, 2007 doi:10.1152/ajpheart.00730.2006.-High-molecular-weight kininogen (HK) and its domain 3 (D3) exhibit anticoagulant properties and inhibit platelet activation at low thrombin concentration in vitro. We hypothesized that the rapid occlusive thrombosis in HK-deficient (HKd) rats following endothelial injury of the aorta results from enhanced platelet aggregation by thrombin. The effects of D3 (G235-M357) or D3-derived peptides on thrombosis in vivo were tested. D3 and its exon 7C terminal peptide (E7CP, K270-Q292), expressed as glutathione S-transferase (GST) fusion proteins (GST-D3, GST-E7CP), or GST alone, as well as cleaved HK (HKa) or synthetic peptide E7CP, were infused intravenously 10 min before endothelial injury. Blood flow was reduced down to 10% of baseline flow within 28 Ϯ 5.2 min by a platelet-fibrin thrombus in GST-treated HKd rats compared with Ͼ240 min in GST-treated normal HK rats (wild type). GST-D3, GST-E7CP, HKa, or E7CP infusion prolonged the flow time to 233, Ͼ240, 223, and Ͼ240 min, respectively, in HKd rats. When GST-E7CP was infused 10 min after the injury, blood flow was maintained for Ͼ240 min. Thrombin-antithrombin concentrations were elevated by injury in HKd rats receiving GST from 35 to 55 g/l and decreased with GST-E7CP, HKa, or E7CP reconstitution to 40, 15, and 9 g/l, respectively. We conclude that HKd rats are prothrombotic and that HKa, kininogen D3, and its fragment E7CP modulate arterial thrombosis after endothelial injury. arterial thrombosis; endothelial injury; kininogen-deficient rat HIGH-MOLECULAR-WEIGHT KININOGEN (HK) and low-molecularweight kininogen (LK) are multifunctional plasma proteins that are substrates for plasma kallikrein and tissue kallikrein yielding bradykinin and kallidin, respectively. The remaining cleaved HK (HKa), lacking bradykinin, exhibits antiadhesive (26) and antiangiogenic (5) activity as well as enhancing cell-associated fibrinolysis (6) and releasing cytokines and chemokines to enhance inflammation (15). Although deficiency of HK results in vitro in a prolonged activated partial thromboplastin time, patients with plasma HK deficiency do not have a hemorrhagic diathesis (4). Whether individuals with total kininogen deficiency are thrombophilic has not been determined because of the rarity of the disorder. However, both kininogens bind to platelets (9,19,25) and selectively inhibit the high-affinity thrombin binding to platelet glycoprotein (GP)Ib (14, 16). Therefore, animal models are the only modality currently available to resolve this issue.Kininogens are proteins composed of multiple domains (Fig. 1A), each with associated functional activities. The heavy chain, domain (D)1-D3, and bradykinin contained in D4 are common to both HK and LK, while the lig...