The Significance of Nitric Oxide: What makes nitric oxide such an important molecule?

Before 1987, the role of nitric oxide (NO) in human health was thought to be primarily as an irritant in air pollution. This view changed dramatically that year with the discovery of the production of NO in the body and the identification of the molecule's key role in biological signaling. In the years since its discovery, over 29,000 scientific papers on NO have been published, which attests to the intensity of research interest devoted to this molecule. In recognition of the medical significance of the molecule, in 1998 the Nobel Prize in Physiology was awarded to the scientists who discovered the role of NO as a biological messenger.

NO is a small gaseous molecule with chemical properties that make it uniquely suitable as both an intra- and intercellular messenger. Because it possesses an unpaired election, NO reacts with other molecules with unpaired electrons, especially superoxide, which can combine with NO to form peroxynitrite, a highly reactive and toxic radical. As a neutral gaseous molecule, NO can diffuse over several cell lengths from its source to exert control over certain enzymes and regulate key cellular functions. Also, because of its reactivity, NO is used as an effector molecule to kill tumors and pathogens. The combined properties of its ability to regulate enzymes across long distances as well as its high reactivity with other molecules give NO its unique dual role as both a powerful signaling molecule and lethal effector molecule.

Because of these powerful functions, the production of this pivotal mediator is tightly regulated and there is ample literature to show that too little or too much NO production contributes to numerous human diseases and disorders. Decreased NO generation in the penis, for example, results in impotence. On the other hand, many other diseases and conditions such as intradialytic hypotension, hemorrhagic shock, tissue rejection, rheumatoid arthritis, and diabetes are associated with the overproduction of NO.