Pulmonary vasoconstrictor response to soluble fibrin in isolated lungs: possible role of thromboxane generation

The blood coagulation system is activated regularly in severe forms of shock, polytrauma, and sepsis. Arising thrombin cleaves the fibrinopeptides A and B from fibrinogen, and it generates monomers of fibrin, which are initially kept in solution by the remaining excess fibrinogen. The effects of soluble fibrin (fibrin monomer/oligomer-fibrinogen complexes) and fibrinopeptides A and B were investigated in blood-free perfused, isolated rabbit lungs. Urea Tris buffer-dissolved fibrin monomers were injected into the pulmonary artery in the presence of circulating excess fibrinogen. In doses above 5 mg, the monomers consistently provoked a sharp rise in pulmonary artery pressure, which was followed by an elevated pressure plateau. Changing to fresh perfusate devoid of soluble fibrin did not restore the pressure to baseline, and a second administration of the soluble fibrin caused a pressor response larger than the first. Only a modest increase in lung weight (less than 2 g) was observed, and lung inflation pressure was not altered. The pressor responses were accompanied by a rapid release of thromboxane A2 and a more delayed release of prostaglandin I2 into the perfusion fluid. A significant correlation between the height of the fibrin-induced pressure rise and the amount of thromboxane release was noted. Inhibition of cyclooxygenase (indomethacin) suppressed the generation of both prostanoids, whereas inhibition of thromboxane synthetase (OKY-046 and imidazole) selectively blocked the liberation of thromboxane. All three inhibitors caused an immediate decline in pulmonary artery pressure, which had been previously elevated due to administration of soluble fibrin, and markedly reduced the pressor response evoked by a subsequent fibrin application in the same lung.(ABSTRACT TRUNCATED AT 250 WORDS)