L-arginine is classified as a conditionally essential amino acid because its endogenous synthesis may not be sufficient to meet metabolic demands in preterm infants and some cases of critical illness

L-Arginine is classified as a conditionally essential amino acid because its endogenous synthesis may not be sufficient to meet metabolic demands in preterm infants and some cases of critical illness. Arginine is required for synthesis of proteins and is a precursor for synthesis of numerous biologically important substances (Fig. 1).

Current interest in L-arginine is focused mainly on its role in biosynthesis of nitric oxide and its stimulatory role in the secretion of insulin and growth hormone. Considerable literature exists from human and animal studies attesting to the fact that L-arginine may lower blood pressure, reduce blood clots and strokes, lower cholesterol and triglycerides, and improve diabetes and sexual functions via its role as a precursor for endothelium-derived nitric oxide.

There is no standard dose of arginine. A common dosage is 2 to 3 grams three times a day. Of the available human studies, doses up to 20 g/day have been generally well tolerated. Many healthy people believe that enhanced intake of arginine has no health risk and they consume chronically arginine 1-3 times daily.

However, excessive consumption of an individual amino acid exerts adverse effects on distribution and metabolism of other amino acids. We evaluated the effect of chronic intake of arginine on amino acid concentrations in blood plasma, liver, kidneys, and muscles of rats fed a standard diet or a high-arginine diet (HAD) for two months. HAD increased blood plasma concentrations of urea, creatinine, arginine, and ornithine and decreased most other amino acids. Arginine and ornithine also increased in muscles and kidneys; an increase of lysine was observed in muscles. Methionine, phenylalanine, threonine, asparagine, glycine, serine, and taurine decreased in most tissues of HAD fed animals.

It is concluded that chronically enhanced arginine intake leads to marked alterations in aminoacidemia in both the blood and tissues. This may impair availability of some amino acids in a number of biochemical pathways and cellular functions, resulting in unexpected responses to various physiological and pathological conditions, such as starvation, exercise, trauma, infection, and cancer development.