Basal nitric oxide modulates vascular effects of a peptide activating protease-activated receptor 2.

Objectives: Protease-activated receptor 2 (PAR2) is a G-protein-coupled receptor proteolytically activated by trypsin, tryptase or factor Xa. Alternatively, PAR2 can be activated by synthetic peptides whose sequence mimics the tethered ligand exposed after receptor cleavage. It is known that PAR2 modulates vascular reactivity, both in vitro and in vivo. The present study was designed to investigate the role of basal nitric oxide and cyclic nucleotides, adenosine 3'5'cyclic monophosphate (cAMP) and guanosine 3'5' cyclic monophosphate (cGMP), in the vasorelaxation induced by a PAR2-activating peptide (PAR2-AP; SLIGRL-NH(2)) on rat aorta in vitro.

Methods: A concentration-response curve to PAR2-AP was performed on rat thoracic aorta with or without a functional endothelium, and the effect of inhibitors was evaluated. The effect of PAR2-AP (10(-7)-3 x 10(-5) M) on endothelium-denuded aorta was also evaluated after tissue incubation with sodium nitroprusside.

Results: PAR2-AP (10(-7)-3 x 10(-5) M) caused an endothelium-dependent relaxation abolished by N(omega)-nitro-L-arginine methyl ester, L-NAME, and by the guanylyl cyclase inhibitor, 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ), but unaffected by geldanamycin. Vasorelaxant effect of PAR2-AP was only partially inhibited by the adenylyl cyclase inhibitor, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536), and it was increased by tissue incubation with the phosphodiesterase inhibitor, rolipram. On tissue without endothelium, PAR2-AP did not cause vasorelaxation, up to a concentration of 10(-4) M. However, after tissue incubation with sodium nitroprusside (SNP, 3 x 10(-9) M), the vasorelaxant effect of PAR2-AP was restored. Following tissue incubation with PAR2-AP, cAMP levels were significantly increased compared to control values.

Conclusions: Our results suggest that vasorelaxation induced by PAR2-AP is modulated by basal nitric oxide with an involvement of both cyclic nucleotides, cGMP and cAMP.