Arginine’s Anabolic Connection

Most bodybuilders are familiar with the amino acid L-arginine because it’s often touted as a “growth hormone” releaser. Various forms of arginine have recently played a starring role in sports supplements used to boost nitric oxide. Since arginine is the main dietary precursor of nitric oxide, it makes sense for NO-boosting supplements to feature it. Increasing NO may boost vasodilation, resulting in an increased muscle pump during training. As I pointed out recently in IRON MAN, NO does a number of other things that are beneficial to health and training.

Arginine is classified as a conditionally essential amino acid. That means the nutritional requirement for arginine rises under certain conditions. Among other functions, arginine is involved in the detoxification of ammonia, which is produced as a result of the metabolism of amino acids. With the participation of arginine, potentially toxic ammonia is converted into urea, which is excreted from the kidneys. 

Arginine is also a glucogenic amino acid, meaning that it can be converted into glucose, the circulating form of sugar in the blood. That process happens in the liver and is called gluconeogenesis. Arginine is involved in the synthesis of various important body compounds, such as creatine, polyamines, ornithine and citrulline. Adding arginine to creatine supplements does not offer any benefits, because the limiting factor in the conversion of arginine into creatine is an enzyme rather than arginine itself.

The most overlooked aspect of arginine is its effect on muscle protein synthesis. While the branched-chain amino acids, particularly leucine, are most associated with muscle protein synthesis, all essential amino acids are actively involved in the process. More recent evidence shows that arginine mimics many of the effects of BCAAs in regard to muscle protein synthesis.

One recent study used rabbits as subjects. The authors note that under severe catabolic conditions, such as burn injuries, the requirement for arginine rises. Past studies show that arginine greatly aids wound healing. At first, the effect was attributed to increased growth hormone release. Later, when arginine was identified as the primary source of NO, the increased blood circulation fostered by NO was thought to be the cornerstone of arginine’s healing effects. The most recent studies indicate that the source of arginine’s healing power is its involvement in stimulating protein synthesis. BCAAs are involved in the same thing.

The rabbit study involved wounds to the animals’ skin and muscle. One focus was whether the healing effect of arginine involved increased NO release in the wound area. The researchers gave the animals a chemical that blocks NO production. That had no effect on the increased muscle protein synthesis that occurred after the animals were given arginine, although the blood flow to the wounded area was markedly reduced, confirming that NO was blocked. The researchers also ruled out increased insulin release, since plasma glucose didn’t decrease, as would have occurred with upgraded insulin release. What they found was that arginine stimulated the movement of amino acids from blood into muscle. That increased amino acid availability and, consequently, muscle protein synthesis.

The downside is that while you can duplicate the results of the experiment in humans, it would require an intake of arginine of 3.1 grams per hour for several hours. A possible side effect would be excess production of NO, resulting in a drop in blood pressure. The main point, however, is that arginine spurs muscle protein synthesis independent of NO—one more aspect of a versatile amino acid. Also consider that the dose suggested above is about what many bodybuilders take anyway in various protein or NO supplements. The muscle protein synthesis effect is a bonus of getting a lot of arginine. IM

 

Zhang, X.J., et al. (2008). The anabolic effect of arginine on proteins in skin wound and muscle is independent of nitric oxide production. Clin Nutr. In press.