Thrombin receptor agonist peptide (TRAP-14) is a 14-amino acid peptide agonist of the α-thrombin receptor. It induces aggregation of washed platelets as well as platelets in citrated and hirudin plasma. TRAP-14 (100 μM) increases the cytosolic calcium concentration in isolated guinea pig pulmonary smooth muscle cells 5-fold over baseline. It increases pulmonary arterial pressure in isolated guinea pig lung when used at a concentration of 1 μM, which is comparable to the effect induced by 10 nM α-thrombin. TRAP-14 also induces contraction of isolated rat aortic rings and increases endothelin-1 (ET-1) levels in a dose-dependent manner, an effect that is reversed by the ETA antagonist BQ-123 and the nitric oxide synthase (NOS) inhibitor L-NNA .