At low concentrations, it functions physiologically as a neurotransmitter and hormone that causes vasodilation
At high concentrations, it combines with O2 or O2- to form additional reactive and toxic species that contain both nitrogen and oxygen (RNOS)
RNOS involved in neurodegenerative diseases (e.g. Parkinson disease) and in chronic inflammatory diseases (e.g. Rheumatoid arthritis)