Citrulline, a biomarker of intestinal mass and absorptive function, has demonstrated efficacy in ameliorating chronic hypoxia-induced pulmonary hypertension [28] and celiac artery obstruction-induced increases in lipid peroxidation, MPO, and inducible nitric oxide synthase (NOS) activity in the stomach [29]. Here, MPO is linked to pulmonary arterial hypertension.