Endothelial-dependent vasorelaxation in freshly isolated aortic rings. Rings from the thoracic aorta of wild-type (n = 5), Par1–/– (n = 5), Par4–/– (n = 4), Par1–/–;Par4–/– (n = 4) mice were tested for vasorelaxation in response to 100 nM thrombin (“Materials and methods”). Data are means ± SE expressed as percentage of relaxation to 100 μM acetylcholine.