A Conditionally-Essential Amino Acid Arginine is essential in humans during the early phase of active growth. Sometime after the infancy and early childhood, the body develops the ability to manufacture arginine from the amino acid citrulline through a process which requires aspartic and glutamic acid.
Under conditions of elevated physical stress, such as during tissue repair, the pathway to the body's synthesis of arginine may not keep up with demand. In such times, additional arginine must come from the diet for optimal health. For this reason, arginine is sometimes called a "conditionally essential" amino acid. The body uses arginine to produce additional citrulline and glutamic acid. Arginine is found in meat, eggs, milk products, and in nuts and seeds, such as peanuts, cashew nuts, pecans and almonds. Ornithine is plentiful in dairy products, meat, and fowl. Little of either amino acid is supplied by cereal grains. One reason that very low protein diets are often associated with less than optimal immune functioning is that, unless such diets are very carefully selected, they will tend to be poor sources of arginine and ornithine. The 1-2 Punch for Protein and Creatine Synthesis Much of the present knowledge regarding arginine and ornithine comes from experiments in which it was discovered that supplemental arginine reduced the weight loss associated with the trauma of large wounds, surgery and burns. Recovery from injury and physical trauma was shown to place a large demand upon the available sources of arginine.
An interesting finding which linked arginine to immune functioning was the discovery that in both injured and uninjured animals, supplemental arginine increased both the size and the activity of the thymus gland. Various researchers subsequently came to view arginine as being a safe nutritional support for immune function, healing and thymic support, particularly under conditions of stress. Under such conditions, there is a greater rate of protein turnover in the body, and therefore there is also a greater need for arginine and ornithine to support protein synthesis. Another nutritional use for arginine and ornithine is to support the interaction of the hypothalamus and the pituitary in the role of these organs in producing and releasing growth hormone (GH). As a GH compound which helps to improve the release of GH, ornithine is roughly twice as effective as arginine. Probably more important to athletes is the fact that the liver naturally produced the short-term energy molecule creatine from arginine and glycine. Creatine must constantly be replenished in muscle, and therefore having on hand adequate amounts of arginine is crucial to reducing recovery time and maximizing gains from training. Other high-energy compounds found in muscle, including guanidophosphate and phosphoarginine also depend upon and are derived from arginine. Support for Sexual Health Arginine has both old and new roles in promoting the sexual health of both men and women. In men, adequate arginine levels long ago were discovered to be supportive of the health and motility of sperm. Similarly, dietary experiments with female animals demonstrated that arginine is important for proper ovarian weights and normal ovulation. Arginine, in other words, supports fertility in both sexes. More recently, the focus of research has shifted to how arginine acts as a building block for the production of the chemical known as nitric oxide (NO). Nitric oxide is intimately involved in the regulation of blood pressure, the control of muscle activity and in regulating erections in males. Nitric oxide has a place in the woman's sexual response as well. Supplemental arginine allows the body to respond fully to physiologic signals which control sexual arousal. In light of this information, it is interesting that arginine exists in a free state in garlic and ginseng, two famous sexual tonics. Liver Detoxification In the detoxification pathway known as the urea cycle, ornithine, like arginine, is essential. Arginine is required to stimulate the activity of the first enzyme of the cycle (carbamyl phosphate) and thus start the cycle. The whole cycle is required to remove excess ammonia - a byproduct of protein metabolism - from the tissues. Ammonia is toxic to the brain and the liver and must be excreted from the body in the urine. The urea cycle more generally controls the transport, storage and excretion of nitrogen. Because of this, arginine and ornithine exert influence over how the other amino acids are used physiologically. Heart Health Some evidence links arginine to proper cholesterol and insulin metabolism. The most notable benefit is with regard to support of blood pressure regulation by means of improved nutritional support for nitric oxide production. This may be especially important to circulation within the brain. Source: Jarrow Formulas
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Scientific References Anderson HL, Soon Cho E, Krause PA, Hanson KC, Krause GF, Wixom RL. Effects of dietary histidine and arginine on nitrogen retention of men. J Nutr. 1977 Nov; 107(11):2067-77. Barbul A, Rettura G, Levenson SM, Seifter E. Arginine: a thymotropic and wound-healing promoting agent. Surg Forum. 1977;28:101-3. Bratusch-Marrain P, Bjorkman O, Hagenfeldt L, Waldhausl W, Wahren J. Influence of arginine on splanchnic glucose metabolism in man. Diabetes. 1979 Feb;28(2): 126-31 Guoyao WU, Morris M. Arginine metabolism: nitric oxide and beyond. J Biochem 1998;336:1-17. Jungling ML, Bunge RG. The treatment of spermatogenic arrest with arginine. Fertil Steril. 1976 Mar;27(3)282-3. Keller DW, Polakoski KL. L-arginine stimulation of human sperm motility on vitro. Biol Reprod. 1975 Sep;13(2):154-7. Morris JG, Rogers QR. Ammonia intoxication in the near-adult cat has a result of a dietary deficientcy of arginine. Science. 1978 Jan 27;199(4327):431-2. Sugano M, Ishiwaki N, Nakashima K. Dietary protein-dependent modification of serum cholesterol level in rats. Significance of the arginine/lysine ratio. Ann Nutr Metab. 1984;28(3):192-9 Zieve L. Conditional deficiencies of ornithine or arginine. J Am Coll Nutr. 1986;5(2):167-76.
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