THROMBIN RECEPTOR ACTIVATION PEPTIDE INDUCES PULMONARY VASOCONSTRICTION

We investigated the involvement of the 11-residue thrombin receptor ac tivating peptide SFLLRNPNDKYEPF (TRAP-14) in mediating the pulmonary v asoconstriction in response to alpha-thrombin. Isolated guinea pig lun gs were uniformly perfused with Ringer-albumin solution at a constant flow of 28 ml/min. Addition of TRAP-14 or human alpha-thrombin to the perfusate caused dose-dependent increases of pulmonary arterial pressu re within 1 min. TRAP-14 at 1 mu M increased pulmonary arterial pressu re to a similar extent as 10 nM alpha-thrombin (i.e., increase of 7.7 +/- 0.8 and 7.4 +/- 0.9 cmH(2)O from baseline, respectively). The incr eases in pulmonary venous resistance induced by TRAP-14 and alpha-thro mbin were two- to fivefold greater than the increases in pulmonary art erial resistance, indicating that both agonists mediated pulmonary hyp ertension secondary to pulmonary venoconstriction. Stimulation of cult ured guinea pig pulmonary artery smooth muscle cells with 100 mu M TRA P-14 or 10 nM alpha-thrombin increased cytosolic Ca2+ concentration ab out five- to sevenfold over baseline. The increase in cytosolic Ca2+ c oncentration in smooth muscle cells was not observed with a subsequent challenge with either agonist, indicating desensitization. In the per fused lungs, an initial stimulation with alpha-thrombin or TRAP-14 des ensitized the lungs to either agonist. The alpha-thrombin-desensitized lungs remained refractile to alpha-thrombin after 1 h of perfusion wi th fresh Ringer solution, whereas the TRAP-14-desensitized lungs recov ered 79% of the vasoconstrictor response by 10 min and 93% of the resp onse by 30 min. Therefore pulmonary vasoconstriction mediated by alpha -thrombin is the result of cleavage of the thrombin receptor, producin g a new NH2-terminal ''tethered ligand'' that contains the receptor ac tivating sequence SFLLRNPNDKYEPF. Furthermore, pulmonary vasoconstrict ion induced by alpha-thrombin involves direct activation of the thromb in receptor on smooth muscle cells.