NOS2 and myocardial infarction: In summary, the mechanism of PO for treatment of MI may be that PO activates the MAPK/ERK signaling pathway, downregulating the expression of such apoptosis-related proteins as bax, caspase3 and caspase9; improving myocardial inflammation; increasing the NOS activity and NO level in serum to dilate blood vessels and increase the myocardial blood flow and oxygen supply.