Abrogation of thrombin-induced increase in pulmonary microvascular permeability in PAR-1 knockout mice

We investigated the function of proteinase-activated receptor-1 (PAR-1) in the regulation of pulmonary microvascular permeability in response to throm bin challenge using PAR-1 knockout mice (-/-). Lungs were isolated and perf used with albumin (5 g/100 ml)-Krebs solution at constant flow (2 ml/min). Lung wet weight and pulmonary artery pressure (P-pa) were continuously moni tored. We determined the capillary filtration coefficient (K-fc) and I-125- labeled albumin (BSA) permeability-surface area product (PS) to assess chan ges in pulmonary microvessel permeability to liquid and albumin, respective ly. Normal and PAR-1-null lung preparations received in the perfusate: 1) t hrombin or 2) selective PAR-1 agonist peptide (TFLLRN-PNDK-NH2). In control PAR-1 (+/+) mouse lungs, I-125-albumin PS and K-fc were significantly incr eased over baseline (by similar to7- and 1.5-fold, respectively) within 20 min of alpha -thrombin (100 nM) challenge. PAR-1 agonist peptide (5 muM) ga ve similar results, whereas control peptide (5 mM; FTLLRN-PNDK-NH2) was ine ffective. At relatively high concentrations, thrombin (500 nM) or PAR-1 ago nist peptide (10 muM) also induced increases in P-pa and lung wet weight. A ll effects of thrombin (100 or 500 nM) or PAR-1 agonist peptide (5 or 10 mM ) were prevented in PAR-1-null lung preparations. Baseline measures of micr ovessel permeability and Ppa in the PAR-1-null preparations were indistingu ishable from those in normal lungs. Moreover, PAR-1-null preparations gave normal vasoconstrictor response to thromboxane analog, U-46619 (100 nM). Th e results indicate that the PAR-1 receptor is critical in mediating the per meability-increasing and vasoconstrictor effects of thrombin in pulmonary m icrovessels.