MAPK3 and pulmonary arterial hypertension: After sustained hypoxic exposure, the expression of 12-LO metabolite, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], was obviously elevated, resulting in enhanced proliferation of PASMCs of rats via inducing ERK1/2 phosphorylation but not p38 (Fig. 6, middle, hormonal responses).335 These findings indicate the potential contribution of 12-LO- ERK1/2 pathway to the development of HPVR and subsequent pulmonary hypertension.