The amino acid L- Arginine, is a semi-essential amino acid that plays an important role in cell division. It helps support the immune system, growth hormone and sperm production, ammonia detoxification and fat metabolism. It also maintains the body's normal physiology to recover from wounds and build muscle. It is an important factor in muscle metabolism and works to transport, store and excrete nitrogen. It is a precursor for nitric oxide, which promotes increased circulation by relaxed blood vessels.
L-Arginine as a sports supplement...
As with most sport supplements, there have been only a few properly designed studies to evaluate the effects of arginine on performance. In some of these trials, a significant increase in strength has been observed. Some earlier studies were conducted which were unable to demonstrate an effect of oral arginine on growth hormone. It is clear however from the studies that under some circumstances oral arginine can influence the secretion of growth hormone. The doses required will be of the order of 30 grams per day in an adult.
An increase in energy about 15 to 20 minutes after taking preparations containing significant levels of arginine is a common observation which athletes have noticed. The basis of this effect is probably through increases in blood glucose and increased uptake of glucose into the cell. The possible mechanisms for this include the use of arginine as an alternative energy source through transamination, an increase in excretion rate of insulin without a concomitant inhibition in glucagon activity and a decrease in plasma ammonia levels through stimulation of urea production.
Arginine, since it is a major precursor of creatine, would be expected to cause elevated levels of creatine in muscles. Preparations containing arginine in combination with methionine and glycine the other creatine precursors have been used to provide energy - these products might be expected to work via the two mechanisms set out above - namely increased plasma glucose levels and increased muscle creatine concentration. The recent findings that the protein synthesis rate in muscles post exercise is dependant on elevating amino acid supply to the muscle may point to another use for arginine in relation to sport and another reason for the effects that have been anecdotally reported by many different athletes.
Arginine has been shown in many of the studies to increase peripheral circulation, thus, if it is given in conjunction with other preparations which can elevate the plasma levels of amino acids, it will maximise the beneficial effects of exercise on increasing muscle size.
Arginine as a precursor for nitric oxide (NO)...
Perhaps the most important function of arginine is to act as a precursor for nitric oxide (NO). Arginine is converted to citrulline under the influence of NO synthase with the resulting production of NO. The effects of NO in the body are widely varied and have implications in many major diseases.
The amino acid is essential for the conversion of ammonia, a toxic product of protein metabolism, to the non-toxic and easily excreted compound urea. It can also act as a precursor for the synthesis of GABA, a neurotransmitter in the brain. Arginine can increase the secretion of insulin, glucagon and growth hormone. Arginine can also increase the secretion of gastrin, a hormone which, in turn causes the secretion of gastric acid and pepsin, essential for normal digestion. In the immune system, it has been demonstrated that arginine can enhance T-lymphocyte response in humans, while anti-tumour effects have been observed in animals.
Arginine is also a precursor in the synthesis of the polyamines spermine and spermidine. An increase in sperm count has been observed in subjects with oligospermia (low sperm count) when arginine intake has been increased.
