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Arginine and Nitric Oxide

Dr. Karol M.D Article by: Dr. Karol M.D
Date: Feb 26, 2014 · Posted in: Cardiovascular Health, Immunity, Reproductive Health
Arginine and Nitric Oxide

Arginine and Nitric Oxide

In the year 1992 the molecule Nitric Oxide was called the molecule of the year by the scientific community. The reason for this is that it plays an extremely vital role in regulating blood pressure as well as the functionality of the immune system. Furthermore it plays a fundamental role in male (and female) erections. If you are wondering what I mean by female erections, the explanation is that the female clitoris is developmentally equivalent to the male penis (both are derived from the same developmental structure in early neonatal development). And just like the penis gets bigger and erected during arousal so does the clitoris. The mechanism responsible for both of these phenomena are the same. Namely nitric oxide acting on smooth muscle in a relaxatory fashion


The penis, the clitoris as well as the wall of arteries are primarily composed of smooth muscle. Smooth muscle is not under voluntary control like skeletal muscle (i.e. the muscles like the biceps or the quadriceps). When nitric oxide binds to such muscle it causes relaxation. Such relaxation dilates blood vessels. In the heart arteries and in arteries all over the body this means a drop in blood pressure and more blood flow. This is something desirable as more blood means more oxygen and nutrients to the tissues that the arteries supply. In the penis and the clitoris the increased blood flow means that more blood crosses from the arteries into the erectile tissues of these organs. The reason for this is that the blood vessels in these organs are perforated allowing blood to escape from the inside of the blood vessel to the outside into the erectile tissue. This is what cases these organs to get engorged with blood making them hard, erect and more sensitive to touch.


From what I have just stated we can say that nitric oxide is great. It decreases blood pressure, increases blood flow, protects the heart from heart attacks, the brain from strokes and causes harder erections. The catch is that, for one, we can not supplement with nitric oxide. It’s a free radical gas that becomes toxic when in contact with air. Fortunately we can supplement with the precursor of nitric oxide. This molecule, or actually an amino acid, is called Arginine. It can be supplemented in the form of capsules or provided in Arginine rich food like almonds for example.


The other important point is that the capability to synthesize nitric oxide decreases with age, as well as in most chronic disease states like diabetes or hypertension (both very common in our society). This  is also one of the reasons why erectile capability decreases in men as they age (as well as in diabetes and hypertension). Thus it makes utmost sense to supplement with Arginine as we age, especially past the age of 40, and certainly in chronic medical conditions, most of which decrease the capability to produce nitric oxide.


Arginine, which in supplement form is actually L-Arginine, is only absorbed in very small proportions. A much more efficient way to supplement it is to supplement with L-Citrulline. Both molecules are part of the Urea metabolic cycle. Citrulline is absorbed to a much greater degree and after absorption it is easily converted to L-Arginine.


One final point is that the popular (although not always safe) prescription medications like Viagra or Cialis work by prolonging the action of nitric oxide. For the readers of my blogs which may be interested in this mechanism here it is. Nitric oxide enters the cells freely by passing through the plasma membrane. Inside in the cytosol (i.e. the fluid portion of the smooth muscle cell) it stimulates an enzyme called Guanylate Cyclase which upon stimulation produced cyclic GMP (i.e. cyclic guanosine mono-phosphate). This molecule eventually cases the opening of calcium channels in the plasma membrane. The calcium enters the cell and in order to keep a neutral electric charge inside the cell, potassium leaves. The calcium binds to the structural components of the muscle cell responsible for muscle contraction and prevents their functioning. Thus the cell is unable to contract. The consequence is that the cell relaxes and the blood vessel wall (which is composed of these muscle cells) relaxes. Blood rushes in and causes an erection. Drugs like Viagra work by inhibiting the enzyme that degrades cyclic GMP, making it last longer and thus making it cause its effect much longer and in a more intense fashion. This enzyme by the way is called Phosphodiesterase.