The Role of Nitric Oxide


Nitric oxide plays an important role in our body.  Research is still ongoing as we learn more and more about this molecule. Here are some of the actions of nitric oxide to help you understand the importance of having optimal levels of it. 

Nitric oxide (NO) is a free radical produced in our body, mainly in endothelial cells of the blood vessels. The endothelium is the inner lining of our blood vessels. Nitric oxide is also produced in many other cells such as neurons (nerve cells), heart muscle cells, kidney cells, and certain immune cells such as macrophages (1). 

Nitric oxide was formerly known as ‘endothelial-derived relaxing factor’ because it relaxes the smooth muscles in the blood vessels, allowing them to dilate (expand). That means it can regulate blood pressure through the relaxation of blood vessels. It has protective effects, helping prevent atherosclerosis (cholesterol and fat buildup along arteries) and cardiovascular disease. Apart from this important function, nitric oxide is known to play other major roles in our body. 

Nitric oxide helps smooth muscle of blood vessel to help with circulation.
Visual of smooth muscle not relaxed and in relaxed states with Nitric Oxide

How is NO regulated in our bodies?

Nitric oxide (NO) release is increased by dietary factors like arginine, citrulline, and vitamin C. Nitric oxide is produced in our bodies by the NOS pathway, where nitric oxide synthase converts l-arginine into nitric oxide (10).

This pathway is activated by numerous stimuli, such as hormones and stress.

When you consume a diet high in saturated fats, nitric oxide production can become impaired. 

The bioavailability of nitric oxide is reduced by oxidation. Oxidation is a chemical reaction that takes place when a substance comes into contact with oxygen. Nitric oxide is a free radical, an unstable molecule due to its uneven number of electrons. This causes it to react easily with other molecules, particularly oxygen. Antioxidants may protect nitric oxide from destruction, allowing it to act longer or more strongly. Antioxidants are molecules that can donate electrons to free radicals. This would stabilize the free radical and prevent its oxidation and, thus, its destruction. 

What are the benefits of NO for our body functions?

Nitric oxide plays an important role in our body. However, as with any molecule, too much nitric oxide also has negative attributes. Research is still ongoing as we learn more and more about this molecule. Here are some of the actions of nitric oxide to help you understand the importance of having optimal levels of it. 

  • Vasodilator action

Nitric oxide relaxes the smooth muscles in the wall of blood vessels, making them expand. This is known as vasodilation. 

  • Reducing blood pressure

Dilatation of blood vessels reduces blood pressure. How is this possible? When nitric oxide causes vasodilation, it results in the widening of our blood vessels, which causes a decrease in systemic vascular resistance. Systemic vascular resistance (SVR) is the amount of force exerted on the circulating blood by the blood vessels in the body. When the blood vessels widen (increase in diameter), SVR falls. This decrease, along with the increase in blood flow, leads to a reduction in our blood pressure (4). In short, a smaller diameter increases resistance and, consequently, the pressure, whereas dilation by nitric oxide causes expansion, less resistance, and lower pressure.

  • Improving blood flow 

When our blood vessels dilate due to the action of nitric oxide, the blood flow increases. This allows the blood to flow freely to each part of the body. The cells get oxygen and nutrients from the blood. Therefore when the blood flow improves, the oxygen and nutrient supply to all organ systems and their cells also improve. 

Nitric oxide will enhance blood flow to areas in our body that may lack oxygen and nutrients. When our tissues need more oxygen or nutrients (for example – during exercise), the tissues release vasodilators like nitric oxide. It will act on the smooth muscles of the walls of blood vessels, making them widen, thus improving blood flow.

  • Benefits for the heart

Nitric oxide is produced in heart muscle cells. Therefore, it plays a role in regulating our heart function. It regulates the tone of the coronary arteries (blood vessels that supply blood to the heart). Nitric oxide controls thrombogenicity. Thrombogenicity means the tendency of a material to be in contact with the blood to form a clot (6). 

Nitric oxide helps control the contractility of the heart and the heart rate. When nitric oxide dilates the blood vessels, the blood pressure reduces. This takes the strain off our hearts and improves the cardiac output. Following a heart attack, some muscles of the heart die due to ischemia (restricted or reduced blood flow). Nitric oxide plays a role in protecting the heart as it prevents problems that can occur with cardiac remodeling, which happens after a myocardial infarction (heart attack) (5).

  • Neurotransmitter action 

Nitric oxide is a crucial signaling molecule for many biological processes. It acts as a neurotransmitter that transmits signals in the nervous system, both centrally, in the brain, and peripherally, on the motor neurons that control muscles. 

Nitric oxide helps with normal functioning of our brains. Apart from transmitting signals, it improves immunity and the survival of nerve cells. Nitric oxide also positively affects synaptic plasticity, which is the formation and strengthening of connections between brain cells. This means that nitric oxide is involved in brain development and memory formation. It regulates many physiological processes in the brain, which affects our behavior and cognitive function. Nitric oxide also helps control blood flow to our brain and new blood vessel formation (2).

  • Platelet aggregation

Nitric oxide can regulate platelet function. It inhibits platelet adhesion and aggregation, thus reducing clot formation. Nitric oxide released by the endothelium prevents the adhesion of platelets to the blood vessel wall and inhibits the recruitment of platelets to a growing thrombus (clot) (8). 

  • Improves immunity 

Nitric oxide is produced in high amounts by monocytes and macrophages in our blood and body tissues. It is toxic to many germs, such as bacteria, viruses, and other parasites, leading to their destruction. Nitric oxide helps to protect us from various infections and has an anti-inflammatory effect. 

  • Benefit for kidneys

Nitric oxide, being a vasodilator, plays a significant role in our kidneys for the excretory function. Research has found impaired nitric oxide production in patients with chronic renal failure (13).

  • Stimulate the release of growth hormone

Research shows that nitric oxide may increase growth hormone levels by stimulating the secretion of growth hormone-releasing hormone (GHRH). However, its role in growth hormone regulation is not clear (11).

  • Bronchodilator action

Nitric oxide can relax the smooth muscles of airways. This is known as bronchodilation. Research has shown that bronchodilation occurs in guinea pigs with inhaled nitric oxide (12). It can also increase mucus secretion in the airways. 

Now you know how important Nitric oxide is to our body; it plays a vital role in sustaining life. Therefore, it is important to maintain optimal levels of nitric oxide in our bodies.

How can we boost the natural production of nitric oxide in the body?

  • Consuming a diet rich in nitrates 

Nitrates are available in vegetables, dairy products, and meats. Vegetables rich in nitrates include celery, lettuce, beetroot, spinach, and cress. Be aware that nitrates from processed meats can be harmful if consumed excessively for a long period as it produces nitrosamines that can cause cancer. 

  • Antioxidant intake to increase stability of nitric oxide 

Ex: Vitamin C, E, niacin, glutathione, and polyphenols. 

Foods rich in antioxidants include berries, plums, prunes, vegetables like beetroot, carrot, kale, broccoli, and dark chocolate.

  • By taking supplements like Arginine and Citrulline 

These help to produce nitric oxide in the body.

  • Exercise 

Regular exercise improves the endothelial function of blood vessels and increases nitric oxide production. 

In addition, nitric oxide is used in the diagnosis and treatment of various diseases, such as certain cancers, asthma, and chronic inflammation.

Where else can nitric oxide be found?

Nitric oxide is a gas used in ventilators. It is also used to treat newborn babies with respiratory failure due to pulmonary hypertension. When this gas is inhaled by the nose and mouth, it relaxes the smooth muscles of the airways and blood vessels in the lungs. However, nitric oxide is also found in pollution. Too much nitric oxide has negative effects on the body as well.

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