<amino acid>

<biochemistry> An essential amino acid, a major component of proteins and contains the guanido group that has a pKa of greater than 12, so that it carries a permanent positive charge at physiological pH. It becomes an essential amino acid when the body is under stress or is in an injured state.

Depressed growth results from lack of dietary arginine. Arginine deficiency syndrome is observed in human babies born with a phosphate synthetase deficiency. Normal growth and development in these infants are achieved by adding arginine to their diet. Arginine deficiency leads to carbamyl phosphate overproduction in the mitochondria due to inadequate ornithine supply. Arginine-deficient diets in males causes decreased sperm counts. Free and bound arginine are found in abundance in human male sperm and arginine has been found to stimulate sperm motility.

There are two sources of arginine, arginine in the food chain and free-form arginine from supplements. Food-source arginine is found in abundance in turkey, chicken and other meats. Nonfood-source arginine is called L-arginine and is created through a fermentation process which separates arginine from all other proteins. In the presence of food and other amino acids, L-arginine will act like food-source arginine but when L-arginine is separated from its nutrient boundaries by the removal of all other amino acids, then L-arginine undertakes a different role, becoming capable of crossing the blood-brain barrier and stimulating growth hormone release secreted by the anterior pituitary.

Growth hormone serum levels peak during adolescence and begin to drop after age 23. Aging reduces natural growth hormone production, which results in added body fat, reduced muscle tissue, slowed healing, lack of elasticity in the skin and reduced immune function. Human pituitary growth hormone secretion is evidenced in human males, females and children following intravenous administration of 30 grams of arginine (in 30 minutes) in adults and 0.5 grams/kilogram of bodyweight in children. Female response is somewhat higher than male response. Oral administration of L-arginine also results in the release of Human Growth Hormone.

Tumour suppression is evidenced in the presence of L-arginine. In the Barbul study, tumours recurred in 100% of the control animals. But in the arginine-supplemented group, only about 60% of the tumours recurred and the animals with tumours survived longer. Supplementation of arginine in the diet inhibits development and increase in size of cancerous tumours, both chemically induced and naturally occurring.

Insulin can block growth hormone release, so high serum insulin levels are counterproductive to GH release. Insulin itself is capable of stimulating muscle growth, but it also strongly stimulates fat storage. Muscle growth stimulation from insulin is minuscule compared to muscle growth stimulated by growth hormone.

(13 Nov 1997)