SummaryTissue factor (TF) and its specific inhibitor TF pathway inhibitor (TFPI) are produced by vascular smooth muscle cells (SMCs) in vitro and are increased in vivo in atherosclerotic compared to normal vessels. Besides local regulation of the hemostatic balance, this may be related to non-hemostatic TF/protease dependent functions such as SMC proliferation, adhesion and migration. The aim of the study was to compare the expression of both proteins between the contractile (normal adult) and synthetic (neo-intimal) SMC phenotypes.Primary cultures of SMCs isolated from rat thoracic aorta before and 10 days after balloon injury displayed stable characteristics of the contractile and synthetic phenotype, respectively. Synthetic SMCs expressed more TF mRNA than contractile SMCs, but released excess TF in the conditioned medium, so that the cell-associated TF activity measured by a factor Xa generating assay remained similar in the two subtypes. Accordingly, cell surface thrombogenicity measured under blood flow conditions was also similar. The production and release of functional TFPI was enhanced by a factor 3 to 6 (p < 0.01) in synthetic SMCs.A difference in the quantitative expression of TF and TFPI is a new distinctive feature of SMC phenotypes. Matrix-associated TFPI derived from synthetic SMCs may serve as an anchorage for their migration and regulate protease-activated processes during neo-intima formation.

Summary. Active site-inhibited factor VIIa (FFR-rFVIIa) competes with factor VIIa (FVIIa) for binding to tissue factor (TF) and exerts an anti-thrombotic effect. We report an evaluation of the anti-thrombotic properties of FFRrFVIIa in a model of thrombosis involving two thrombogenic surfaces. Uncoated glass capillaries or glass capillaries coated with TF were incorporated into an arterioarterial shunt in the rat and the occlusion time (OT) of the shunt was determined. An anti-thrombotic activity of FFR-rFVIIa was shown only on the TF-coated surface: the OT of the shunt was significantly prolonged, from 167^34 s in control animals to 312^42 s after i.v. bolus administration of 4 mg/kg FFR-rFVIIa. This OT was similar to those observed with the uncoated shunts in untreated animals (353^84 s). In vitro preincubation of the TF-coated shunt with FFR-rFVIIa significantly prolonged the OT to 245^45 s in the absence of detectable amounts of FFRrFVIIa in the plasma. rFFR-rFVIIa weakly prolonged the tail template bleeding time by a factor of 1´5. This effect was more pronounced in animals pretreated with heparin. The anti-thrombotic and prohaemorrhagic effects of FFR-rFVIIa were totally reversed by administration of an equidose of rFVIIa. These results provide new information on the pharmacological properties of FFR-rFVIIa that will be useful for its clinical development.

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