ODC1 and pulmonary arterial hypertension: Metabolomic analysis has reported increased ornithine and PUT in lung tissues from patients with PAH42 and elevated plasma 4-acetamidobutanoate and N-acetyl-PUT have been reported in patients with idiopathic/heritable PAH.43 Recently, ODC mRNA expression was shown to negatively correlate with mPAP in patients with PAH.44 Although abnormal polyamine levels are observed in PAH, it is unclear whether this represents changes in the intracellular or extracellular environment and whether various cell types may exhibit different responses.