Nitric oxide (NO) is a signaling molecule produced in the body through the metabolism of the amino acid arginine. The enzyme nitric oxide synthase (NOS) catalyzes this process, converting arginine into NO and citrulline. This production occurs in various tissues, including the endothelium, where NO plays a crucial role in regulating blood flow and vascular tone. Once produced, NO diffuses quickly across cell membranes and interacts with various targets, including guanylate cyclase, which leads to the production of cyclic GMP (cGMP). This signaling pathway is essential for numerous physiological processes, such as neurotransmission, immune response, and smooth muscle relaxation.