Nitric oxide is a fairly reactive, colorless gas which is often associated with photochemical smog. It is formed when it combines with oxygen in automobile engines.
The Lewis dot structure of NO is given below. Note the unpaired electron on nitrogen making this molecule a free radical.
Until recently this gas was considered an irritating byproduct of industrial processes. Today, thanks to the Nobel Prize winning work of Robert F. Furchgott, Ferid Murad, and Louis J. Ignarro, we know that nitric oxide is essential in signal pathways of our cardiovascular system.
"In 1977, Murad found that nitroglycerin and related drugs induce nitric oxide (NO) formation and that this gas relaxes the muscle cells that narrow and dilate blood vessels. Around 1980, Furchgott found that endothelial cells, which line the interior of blood vessels, produce a signaling molecule that causes nearby muscle cells to relax, thus regulating blood pressure."
The two discoveries where not connected at first because nitric oxide was not considered to have a natural biological role due to its highly reactive nature. It is considered a free radical and as such is known to be very destructive to stable molecules involved in cell metabolism.
"But as Furchgott and Ignarro, working independently, analyzed the nature of the endothelium's relaxing factor, the gas became a prime candidate. At a conference in 1986, each laid out a compelling case that nitric oxide was indeed the factor."
Subsequent research has implicated nitric oxide in a number of physiological roles including:
"Some brain cells communicate using the gas, and immune cells let loose bursts of nitric oxide to kill infectious organisms or cancer cells. By increasing blood flow, nitric oxide even plays a role in penile erections; the celebrated drug Viagra amplifies the actions of the gas."
Physicians administer NO to premature babies whose lungs are not fully developed to help increase blood flow. Nitric oxide reduces the need for oxygen treatment which can damage the infants eyes.
"The NO field has outgrown its original discovery," says Jonathan S. Stamler of the Duke University Medical Center in Durham, N.C., who studies nitric oxide's interactions with hemoglobin. "The impact has been truly remarkable. The ramifications apply to every organ system and cellular response. You name it...and nitric oxide has been implicated."
From diabetes to hypertension, cancer to drug addiction, stroke to intestinal motility, memory and learning disorders to septic shock, sunburn to anorexia, male impotence to tuberculosis, there is probably no pathological condition where nitric oxide does not play an important role. Only recently (within the last 12 years) discovered as a product of enzymatic synthesis in mammals, in 1999 alone there are already nearly 2600 scientific papers dealing with this remarkable molecule and a total of nearly 24,000 in the last five years. Jack R. Lancaster
Considering that too much nitric oxide can damage cells, "it's astounding nature chose it to perform so many functions," adds Lancaster
The molecule even has its own Journal dedicated to the latest developments in its research.