Type 1 plasminogen activator inhibitor binds to fibrin via vitronectin.

Type 1 plasminogen activator inhibitor (PAI-1), the primary inhibitor of tissue-type plasminogen activator (t-PA), circulates as a complex with the abundant plasma glycoprotein, vitronectin. This interaction stabilizes the inhibitor in its active conformation In this report, the effects of vitronectin on the interactions of PAI-1 with fibrin clots were studied. Confocal microscopic imaging of platelet-poor plasma clots reveals that essentially all fibrin-associated PAI-1 colocalizes with fibrin-bound vitronectin. Moreover, formation of platelet-poor plasma clots in the presence of polyclonal antibodies specific for vitronectin attenuated the inhibitory effects of PAI-1 on t-PA-mediated fibrinolysis. Addition of vitronectin during clot formation markedly potentiates PAI-1-mediated inhibition of lysis of (125)I-labeled fibrin clots by t-PA. This effect is dependent on direct binding interactions of vitronectin with fibrin. There is no significant effect of fibrin-associated vitronectin on fibrinolysis in the absence of PAI-1. The binding of PAI-1 to fibrin clots formed in the absence of vitronectin was characterized by a low affinity (K(d) approximately 3.5 micrometer) and rapid loss of PAI-1 inhibitory activity over time. In contrast, a high affinity and stabilization of PAI-1 activity characterized the cooperative binding of PAI-1 to fibrin formed in the presence of vitronectin. These findings indicate that plasma PAI-1.vitronectin complexes can be localized to the surface of fibrin clots; by this localization, they may modulate fibrinolysis and clot reorganization.

NK1 and NK2 receptors mediate tachykinin and resiniferatoxin-induced bronchospasm in guinea pigs.

The present study characterized neurokinin receptor-mediated bronchoconstrictor responses in anesthetized guinea pigs. Thus, we have compared the actions of the selective neurokinin 1 (NK1) (CP-99,994) and neurokinin 2 (NK2) (SR-48,968) receptor antagonists against dose-response curves (DRC) induced by intravenously administered substance P (SP), neurokinin A (NKA), neurokinin B (NKB), beta Ala8-NKA (4-10),Sar9-Met(O2)11SP, and single dose (intravenous) challenge with resiniferatoxin (RTX), a capsaicin-like sensory neurotoxin, leukotriene D4 (LTD4) and antigen. The rank order of potency of the neurokinins for inducing bronchoconstriction was beta Ala8-NKA(4-10) > NKA > Sar9-Met(O2)11Sp > SP >> NKB. The DRC to the selective NK1 agonist Sar9-Met(O2)11SP was shifted to the right 10-fold by the selective NK1 antagonist, CP-99,994 (1 mg/kg, intravenously), but was not shifted by SR-48,968 (3 mg/kg, intravenously). The DRC to the selective NK2 agonist beta-Ala8-NKA(4-10) was shifted to the right 82-fold by the NK2 antagonist, SR-48,968 (1 mg/kg), but was not shifted by CP-99,994 (3 mg/kg, intravenously). SR-48,968 (1 mg/kg) also blocked NKA (3-fold shift) but did not block SP. CP-99,994 failed to produce a significant rightward shift of the DRC to either SP or NKA. However, the combination of 1 mg/kg CP-99,994 and 1 mg/kg SR-48,968 produced significant shifts of the DRCs to SP (> 5-fold) and NKA (> 300-fold). Hypotension induced by NKA and SP was also blocked by this combination.(ABSTRACT TRUNCATED AT 250 WORDS)