Nitric oxide signaling system (NO signaling system)

The Nitric Oxide (NO) signaling system is a fundamental biological pathway that regulates a wide array of physiological processes, most notably vascular tone, neurotransmission, and immune function (Wikipedia, 2024). It is initiated by the synthesis of NO from L-arginine by nitric oxide synthase (NOS) enzymes, including endothelial (eNOS), neuronal (nNOS), and inducible (iNOS) isoforms (MDPI, 2024). Once produced, NO diffuses into target cells and binds to its primary receptor, soluble guanylate cyclase (sGC), which catalyzes the conversion of GTP to cyclic guanosine monophosphate (cGMP) (NIH, 2022). This second messenger then activates protein kinase G (PKG) and other effectors to mediate effects such as smooth muscle relaxation, inhibition of platelet aggregation, and modulation of synaptic plasticity (Cusabio, 2024). Dysregulation of this system, often characterized by reduced NO bioavailability or impaired sGC sensitivity, is a hallmark of cardiovascular diseases like hypertension and heart failure, as well as erectile dysfunction (NIH, 2025). Conversely, excessive NO production during inflammation can lead to tissue damage and hypotension in septic shock (NIH, 2005). Pharmacological agents target this system at multiple levels, including NO donors, sGC stimulators, and PDE5 inhibitors, to restore or enhance signaling for therapeutic benefit (Abcam, 2024).

Other names

NO-sGC-cGMP pathwayNitric oxide pathwayL-arginine-NO pathwayNitric oxide signaling pathway

The system is modulated through several mechanisms: NO donors (e.g., nitroglycerin) release nitric oxide to supplement endogenous levels; soluble guanylate cyclase (sGC) stimulators (e.g., riociguat) and activators (e.g., cinaciguat) increase cGMP production; and phosphodiesterase 5 (PDE5) inhibitors (e.g., sildenafil) prevent the degradation of cGMP, thereby prolonging its signaling effects (Bryan et al., 2009; Abcam, 2024).