What are the effects of nitric oxide in the body?

Nitric oxide (NO), also called nitrogen monoxide, is an important natural component of the biochemistry of mammals, including humans. In normal, healthy mammalian biochemistry, nitric oxide's primary role is as a chemical messenger. Healthy levels of nitric oxide are important for the nervous, circulatory, and immune systems. Although the effects of nitric oxide are essential to human life, excessive levels, either due to endogenous production or environmental exposure, can be toxic.

When the body needs to increase blood flow through the circulatory system, the inner lining of the blood vessels releases nitric oxide into the surrounding smooth muscle tissue in the blood vessel walls. This causes the smooth muscle to relax and induces vasodilation, or widening of the blood vessels. This helps regulate blood flow and blood pressure and allows people to adapt to low-oxygen conditions, such as high altitudes. It also causes penile erection during sexual arousal by increasing blood flow to the genitals in response to sexual stimulation. In addition to affecting smooth muscle, it can also affect cardiac muscle tissue in the heart to slow the heart rate.

In the nervous system, nitric oxide functions as a neurotransmitter to carry messages between neurons and is part of the memory formation and learning process. It is also produced in the stomach, through reactions between stomach acid and nitrate in swallowed saliva, to maintain blood flow to the stomach and sterilize food as it is digested. In the immune system, a type of white blood cell called macrophages produce nitric oxide to poison and kill bacteria.

The effects of nitric oxide can be detrimental to health at excessive levels. It can aggravate sepsis, as the release of large amounts of the chemical by the immune system in an attempt to kill infectious bacteria can cause the amount to increase to cytotoxic levels, damaging the body's own cells. As one of the effects of nitric oxide is vasodilation, excessive levels can cause blood pressure to drop to dangerously low levels, causing the body to go into shock.

Nitric oxide can also be harmful when absorbed into the body from the outside environment, and is a common industrial pollutant. Contact causes irritation of the eyes, skin and mucous membranes. Inhalation can interfere with breathing by causing coughing and shortness of breath, as well as nausea and burning pain in the chest and throat. In addition to initial breathing difficulties, the effects of nitric oxide when inhaled can also include potentially dangerous conditions such as pulmonary edema, the buildup of excess fluid in the lungs, and the blood disorder methemoglobinemia.

Go up