FIGURE 6.

In mammals, there are three isotypes of nitric oxide synthase (NOS) (eNOS, iNOS, and nNOS). ENOS is the most important source of NO in endothelial cells. The shear stress of blood flow on the vascular wall is the main mechanism by which eNOS produces NO. INOS can be induced in a variety of cell types. LPS as a proinflammatory medium can induce the expression of iNOS. At the same time, the transcription factors NF-κB and STAT-1α are believed to be necessary for iNOS transcription in most cells. nNOS is highly expressed mainly in peripheral nerve fibers and is thought to have a protective effect on atherosclerosis. The release of L-Glutamate (L-Glu) from baroreceptors activates nNOS and promotes the production of NO. Although the expression mechanisms of the three isotypes are different, all of them can generate NO and L-Citrulline (L-CCP) as the substrate.