Nitric oxide is produced from?

ANSWER: (A) EndotheliumREF: Guyton's physiology 22nd edition page 199Nitric oxide should not be confused with nitrous oxide (N2O), an anesthetic and greenhouse gas, or with nitrogen dioxide (NO2), a brown toxic gas and a major air pollutant.Nitric oxide, known as the endothelium-derived relaxing factor, or 'EDRF', is biosynthesized endogenously from L-arginine, oxygen and NAD PH by various nitric oxide synthase (NOS) enzymes. Reduction of inorganic nitrate may also serve to make nitric oxide. The endothelium (inner lining) of blood vessels uses nitric oxide to signal the surrounding smooth muscle to relax, thus resulting in vasodilation and increasing blood flow.