L-Ornithine is a nonprotein amino acid. It is used in the body in the biosynthesis of L-arginine, L-proline and polyamines. L-Ornithine is a basic amino acid, positively charged at physiological pH. It is also known as alpha,delta-diaminovaleric acid and 2,5-diaminopentanoic acid. The molecular formula of L-ornithine is C5H12N2O2, and its molecular weight is 132.16 daltons. The structural formula is:
L-Ornithine is used as a nutritional supplement principally for its putative anabolic activity. There is little evidence to support this use. However, a derivative of L-ornithine called ornithine alpha-ketoglutarate or OKG (see Ornithine Alpha-Ketoglutarate) may, under certain conditions, have immunomodulatory and anticatabolic and/or anabolic actions.
Actions & Pharmacology
L-Ornithine has putative anabolic, immunomodulatory and wound-healing activities.
Mechanism of Action
L-Ornithine may at very high doses—around 30 grams—stimulate the pituitary release of growth hormone by virtue of its metabolism to L-arginine (see L-Arginine).
Burn injury and other traumas affect the status of L-arginine in the various tissues of the body. De novo synthesis of L-arginine during these conditions is probably not sufficient for normal immune function, nor for normal protein synthesis. Under these conditions, L-ornithine may have immunomodulatory and wound-healing activities, again, by virtue of its metabolism to L-arginine.
Following ingestion, L-ornithine is absorbed from the small intestine via a sodium-dependent active transport process. The transport system for L-ornithine is shared with L-arginine, L-lysine and L-cystine. L-ornithine is transported via the portal circulation to the liver where it undergoes extensive metabolism to L-arginine, polyamines and proline, among other metabolites. L-Ornithine that is not metabolized in the liver is distributed by the systemic circulation to the various cells of the body.
Indications & Usage
It is claimed that ornithine has anabolic effects and improves athletic performance, that it has wound-healing effects and is immuno-enhancing. There is little support for these claims. There is at least preliminary evidence, however, that the better-studied ornithine alpha-ketoglutarate may have some of these activities. Inasmuch as ornithine is metabolized to arginine, which also demonstrates some of these effects, it is possible that ornithine, when more thoroughly studied, might exhibit some similar effects. See Arginine and Ornithine Alpha-Ketoglutarate.
Those who use L-ornithine take doses of 500 milligrams to 2 grams, usually before bedtime and on an empty stomach. Some combine L-ornithine with similar doses of L-arginine.
LiteratureBarbul A. Arginine: biochemistry, physiology, and therapeutic implications. J Parenter Enteral Nutr. 1986; 10:227-238.Bucci L, Hickson JF Jr, et al. Ornithine ingestion and growth hormone release in bodybuilders. Nutr Res. 1990; 10:239-245.Bucci LR, Hickson JF Jr, Wolinsky I, Pivarnik JM. Ornithine supplementation and insulin release in bodybuilders. Int J Sport Nut. 1992; 2:289-291.DeBandt J-P, Coudray-Lucas C, Lioret N, et al. A randomized controlled trial of the influence of the mode of enteral ornithine alpha-ketoglutarate administration in burn patients. J Nutr. 1998; 128:563-569.Elam RP, Hardin DH, Sutton RA, Hagen L. Effects of arginine and ornithine on strength, lean body mass and urinary hydroxyproline in adult males. J Sports Med Phys Fitness. 1989; 29:52-56.Fogelholm GM, Naveri HK, Kiilavuori KT, Harkoner MH. Low-dose amino acid supplementation: no effects on serum human growth hormone and insulin in male weightlifters. Int J Sport Nutr. 1993; 3:290-297.Iwasaki K, Mano K, Ishihara M, et al. Effects of ornithine or arginine administration on serum amino acid levels. Biochem Int. 1987; 14:971-976.Jeevanandam M, Holaday NJ, Petersen SR. Ornithine alpha-ketoglutarate (OKG) supplementation is more effective than its component salts in traumatized rats. J Nutr. 1996; 126:2141-2150.Lambert MI, Hefer JA, Millar RP, Macfarlane PW. Failure of commercial oral amino acid supplements to increase serum growth hormone concentrations in male body builders. Int J Sport Med. 1993; 3:298-305.Torre PM, Ronnenberg AG, Hartman WJ, Prior RL. Supplemental arginine and ornithine do not affect splenocyte proliferation in surgically treated rats. J Parenter Enteral Nut. 1993; 17:532-536.
Research & Summary
In one double-blind, placebo-controlled study, a combination of 1 gram of arginine and 1 gram of ornithine daily, used in conjunction with a high-intensity strength-training program over a five-week period, increased total strength and lean body mass in adult males, compared with controls. Most trials using ornithine alone, however, have reported no significant anabolic effects. Most of these studies have failed to show that ornithine supplementation has any significant effect on insulin secretion or human growth hormone levels in bodybuilders. There is apparently only one study reporting that ornithine increased growth hormone levels in bodybuilders, and this study used a very high dose of the supplement (13 grams daily). Numerous gastrointestinal side effects were associated with this dosage.
Contraindications, Precautions & Adverse Reactions
L-Ornithine is contraindicated in those with a deficiency of ornithine-delta-aminotransferase. This is a genetic disorder resulting in gyrate atrophy of the choroid and retina and progressive blinding chorioretinal degeneration. It is rare.
L-Ornithine is also contraindicated in those hypersensitive to any component of an ornithine-containing supplement.
Pregnant women and nursing mothers should avoid L-ornithine supplementation.
Doses higher than 10 grams daily may cause such gastrointestinal symptoms as nausea, abdominal cramps and diarrhea.