| |
Arginine |
|
| Arginine is one of the 20 most common natural amino acids. Arginine, like most amino acids, can have one of two forms, called the L-form and the D-form. These two forms are mirror images of each other, with the L-form molecule rotating in a spiral to the left and
the D-form spiralling to the right. The L-form of arginine (and most other amino acids) is more compatible with human biochemistry, such that L-arginine is the only form recommended. L-arginine is a protein amino acid present in the proteins of all life forms. It is classified as a semi-essential or conditionally essential amino acid. This means that under normal circumstances the body can synthesize sufficient L-arginine to meet physiological demands. Even so, arginine is often classed as one of the 10 essential amino acids, it is usually considered essential to the diet of children for the maintenance of normal rates of growth. Arginine is involved in numerous areas of human biochemistry, including ammonia detoxification, hormone secretion, and immune modulation. Arginine is the direct metabolic precursor of urea, the dominant nitrogenous waste product of most mammals. Arginine is synthesized in mammals from glutamine via pyrroline 5-carboxylate (P5C) synthetase and proline oxidase in a multi-step metabolic conversion. In adults, most endogenous arginine is derived from citrulline, a by-product of glutamine metabolism in the gut or liver. Citrulline is released into the circulation and taken up primarily by the kidney for conversion into arginine. Arginine can be decarboxylated, yielding agmatine. Conversion by nitric oxide synthase to citrulline also yields the vasoactive mediator nitric oxide. Dietary intake remains the primary determinant of plasma arginine levels, since the rate of arginine biosynthesis does not increase to compensate for depletion or inadequate supply. Arginine contains four nitrogen atoms per molecule, making it the most abundant nitrogen carrier in humans and animals. Arginine has a number of functions in the body such as assisting in wound healing, hormone production, immune function and removal of excess ammonia. |
| |
Arginine functions, uses, and health benefits |
|
| Arginine is involved in multiple areas of human physiology and metabolism. Arginine plays an important role in cell division, the healing of wounds, removing ammonia from the body, immune function, and the release of hormones. L-arginine, is an immune system enhancer. It stimulates the thymus gland, boosts white blood cell production and stimulates release of growth hormone. L-arginine is used by the immune system to help regulate the activity of the thymus gland, which is responsible for manufacturing T
lymphocytes. Arginine is needed to increase protein synthesis, which can in turn increase cellular replication. Therefore, arginine may help people with inadequate numbers of certain cells. Although it is not a major inter-organ shuttle of nitrogen, arginine nevertheless plays an important role in nitrogen metabolism as an intermediate in the urea cycle, making it essential for ammonia detoxification.
The body uses arginine to produce nitric oxide. Nitric oxide is an endogenous messenger molecule involved in a variety of endothelium-dependent physiological effects in the cardiovascular system. Nitric oxide is an important regulator of vasomotor function in the gut. Inadequate concentration of nitric oxide leads to vasoconstriction of the intestinal vessels, which might lead to ischemia and a predisposition to NEC. Secondly, nitric oxide acts as a neurotransmitter for enteric non-adrenergic non-cholinergic neurons that regulate peristalsis. Lack or inadequacy of nitric oxide can alter intestinal motility. Nitric oxide inhibits leucocyte adherence and modulates the inflammatory responses in the intestine to various insults. Because of arginine's nitric oxide-stimulating effects, it can be utilized in therapeutic regimens for angina pectoris, congestive heart failure, hypertension, coronary heart disease, preeclampsia, intermittent claudication, and erectile dysfunction.
Arginine may be of benefit in individuals with human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS). Patients with congestive heart failure (CHF) have reduced peripheral blood flow at rest, during exercise, and in response to endothelium-dependent vasodilators. Nitric oxide formed from arginine metabolism in endothelial cells contributes to regulation of blood flow under these conditions. Arginine supplements appear to reduce mildly elevated blood pressure by enhancing the synthesis of nitric oxide (a gas) in the cells that line the blood vessels. This helps dilate vessel walls and improve blood flow around the heart. Arginine supplementation may reduce the risk of atherosclerosis. Arginine has been found to increase blood flow to the heart and improve the chest pains caused by angina in some patients. Arginine may help stimulate the activity and increase the size of the thymus gland, which begins to decrease in size after puberty. Arginine is known to stimulate growth hormone release and has been said to increase muscle mass and fat loss. Human growth hormone is secreted by a gland in the brain and has a direct effect on metabolism by increasing the levels of fat and glucose burnt for energy. |
| |
Dietary sources of arginine |
|
There are two sources of arginine, arginine in the food chain and free-form arginine from supplements. Dairy products, meat, poultry and dish are all excellent sources of arginine. Many nuts and chocolate also contain significant amounts of arginine. It is available in powder, tablet or capsule form, and is sold either alone or in conjunction with other amino acids. Nonfood-source arginine is called l-arginine and is created through a fermentation process which separates arginine from all other proteins 1000.
|
| |
Arginine dosage, intake |
|
Most people do not need to take extra arginine. Normally, the body makes enough arginine, even when it is lacking in the diet. Most studies on arginine have used between 2-30 grams per day. Arginine is also sometimes combined with arginine prior to physical activity. Most research on cardiovascular disease has used between 6 and 20 grams per day. Optimal intakes remain unknown and are likely to vary depending upon the individual. Each person has biochemical individuality, and significantly differing needs for amino acid supplements, appropriate amounts must be determined by a doctor. |
| |
Arginine deficiency |
|
Because arginine is produced naturally by the body, most people do not need to take extra supplements. However, during times of unusual stress or injury, the body may not be able to produce the necessary amount of arginine. Deficiency produces symptoms of muscle weakness, similar to muscular dystrophy. Arginine-deficiency impairs insulin production, glucose production, and liver lipid metabolism. Conditional deficiencies of arginine or ornithine are associated with the presence of excessive ammonia in the blood, excessive lysine, rapid growth, pregnancy, trauma, or protein deficiency and malnutrition. Arginine deficiency is also associated with rash, hair loss and hair breakage, poor wound healing, constipation, fatty liver, hepatic cirrhosis, and hepatic coma.
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 is found in abundance in human male sperm and arginine has been found to stimulate sperm motility. |
| |
Toxicity, side effects, interactions, and contraindications |
|
Arginine has so far appeared to be free of obvious side effects. There are no known signs of toxicity from arginine. The most common adverse reactions of higher doses (from 15 to 30 grams daily) are nausea, abdominal cramps and diarrhea. Some may experience these symptoms at lower doses. However if administered too rapidly, flushing, nausea, vomiting, numbness, headache and local venous irritation may occur. Arginine is contraindicated in patients with allergic tendencies and hyperchloraemic acidosis. Oestrogens and progestin-oestrogen combination oral contraceptives may eleviate growth hormone response. Medroxyprogesterone acetate may reduce growth hormone response. Norethindrone may reduce insulin response. |
|
|
|
|
