TRYPSIN-INDUCED AND SLIGRL-INDUCED VASCULAR RELAXATION AND THE INHIBITION BY BENZAMIDINE DERIVATIVES

Serine proteinases are involved in several physiological processes and elicit profound cellular effects in a variety of tissues. Besides the thrombin receptor a second receptor, activated by trypsin, the protei nase-activated receptor 2 (PAR-2), was cloned and characterized. Both enzymes generate a new extracellular N-terminus by limited proteolytic cleavage which functions as tethered ligand to activate the receptor. Synthetic peptides corresponding to the sequences of the newly genera ted N-terminus are able to mimic the effects of the enzymes. In porcin e pulmonary arteries trypsin and the receptor-derived peptide SLIGRL e licited an endothelium-dependent transient relaxation of PGF(2 alpha)- precontracted vessels. The EC50 values for trypsin and SLIGRL amounted to I.1 +/- 0.2 nM and 5.4 +/- 0.6 mu M, respectively. Trypsin and SLI GRL caused a homologous desensitization but thrombin and the thrombin receptor-activating peptide SFLLRN were still able to elicit pronounce d relaxant effects. The trypsin-and SLIGRL-induced relaxant responses were markedly diminished after blockade of the nitric oxide synthesis by N-G-nitro-L-arginine methyl ester (200 mu M) and were absent in end othelium-denuded vessels. Indomethacin and hirudin did not influence t he relaxant effects. The effect of trypsin but not that of SLIGRL was blocked by the proteinase inhibitor aprotinin suggesting that only pro teolytically active trypsin activates the receptor. Benzamidine deriva tives of the 3-amidinophenylalanine type with different affinity for t rypsin and thrombin inhibited the vascular effects of trypsin (IC50 0. 007-0.7 mu M) correlating with its antitrypsin activity. The data sugg est that the vascular effects of trypsin and SLIGRL are mediated throu gh activation of PAR-2 which differs from the thrombin receptor.