Structural Biochemistry/Nitric Oxide
Nitric oxide is a unique gas that serves as a chemical messenger in the human body. In contrast to proteins and neurotransmitters, nitric oxide is rather difficult to analyze due to its volatile nature (Proteins and neurotransmitters are readily extracted and remain intact for hours; whereas, nitric oxide vanishes in seconds).
NO In The Body
Nitric oxide is very important in the physiological aspects of the body, including cell to cell communication in the nervous system, as well as functioning in the immune system. It is particularly important in the physiology of the brain.  The role of Nitric Oxide in cells is as a chemical messenger. NO, however, vanishes in seconds, such volatility renders NO a molecule with extraordinary diversity. Because of its nature, nitric oxide can perform specific functions such as open blood vessels, help pass electrical signals between nerves, and most importantly, fight off infections. For example, nitric oxide is the active substance in INOmax, a drug that is delivered by inhalation. The drug is a pulmonary vasodilator, meaning it will increase the flow of blood in the lungs by relaxing the muscles and opening the blood vessels wider.
The production of this gas is primarily controlled by an enzyme called nitric oxide synthase (NOS). Tiny and hard to study in the laboratory, NO eluded scientists for many other years because other molecular messenger such as neurotransmitters and larger proteins can be relatively easily extracted from body fluids and studied where they can remain intact for minutes or even hours. Scientists and researchers used X-ray crystallography to understand the shape and structure of NOS, and how it binds to specific substrates.
From this, they were able to determine how to boost or inhibit the activity of nitric oxide. However, the production of nitric oxide must be controlled in order for it to be most effective. For instance, opening the blood vessels too widely can result in a deadly shock in which there is not enough blood flowing through to fill the organs. At high levels it can cause neurological stress as well as cell death. This shows that NO can also be a foe, too much or too little of this gas can be harmful. An overactive immune response, fired up by NO, can produce a painful syndrome called inflammatory bowel disease. With all this at stake, the body works hard to stringently control production of this powerful gas. . Fatal symptoms can also include hypertension, irregular heart beatings, and drop in blood pressure. .
NO As A Supplemental Drug
Nitric oxide has become an extremely popular drug in the bodybuilding world. Taking nitric oxide supplements leads to increased blood flow to the muscles, which will let a greater amount of nutrients be delivered to the muscles while working out. Taking nitric oxide also affects the endocrine system's gonadotroptin releasing hormone, as well as the release of adrenaline. Nitric oxide supplements usually contain the amino acid Arginine. Taking too much of arginine can lead to weakness, diarrhea, nausea, and feelings of tiredness. It is important to monitor the amount of nitric oxide supplements being taken in order not to overdose. 
- Jelena Bašić, et al. "Nitric Oxide - Mediated Signalization And Nitrosative Stress In Neuropathology." Journal Of Medical Biochemistry 31.4 (2012): 295-300.
- Berg, Jeremy M., ed. (2002), Biochemistry (6th ed.) New York City, NY: W.H. Freeman and Company,
- U.S. Department of Health and Human Services. Chemistry of Health. October 2006.<http://www.nigms.nih.gov>.