NNMT and pulmonary arterial hypertension: As the NNMT activity in the lungs was approximately 80-fold lower than in the liver, the major source of MNA release responsible for the nearly 4-fold increase in plasma MNA concentration seen in advanced PAH may be most likely ascribed to the activation of the NMMT-MNA pathway in the liver, despite the fact that NNMT is also present in other tissues [1, 2].