In adults, L-arginine and L-ornithine are "non-essential" Amino Acids which means the body can make its own supply of them. However a dietary supply of L-arginine is thought to be essential for children because not enough can be made by the juvenile body for the requirements of growth.
Like most other Amino Acids, L-arginine is a component of body proteins. However, L-ornithine is unusual in that it is not incorporated into proteins.
L-arginine and L-ornithine both play an important part in the urea cycle, which detoxifies ammonia (1). The liver, which contains all the relevant enzymes in proper proportions, is by far the most important site of urea cycle reactions.
L-arginine and L-ornithine also have the physiological role of stimulating the pituitary gland to release growth hormone (2). Growth hormone is very important in the growth and development of children and in the addition of muscle in adults. It also has the effect of improving the immune function of the thymus gland and stimulating Wound healing.
L-arginine is the precursor of two substances found in sperm called spemidine and spermine. The amino acid is an extremely rich component of seminal fluid, making up 80% of this substance.
Several studies have reported the treatment of male Infertility with arginine supplements. L-arginine may help to alleviate male infertility, improving sperm production and motility (2).
Wound healing may also be speeded up by supplementing with L-arginine and/or L-ornithine (3,4). It appears that these two Amino Acids stimulate the formation of collagen - the important connective tissue in Skin.
The theory that oral supplements of L-arginine and L-ornithine can help to "slenderise" the body through burning fat and stimulating muscle formation is not borne out by research (2). For any effect in this area, high levels of
L-arginine and L-ornithine would be needed intravenously.
L-arginine improves the bioavailability of nitric oxide (a powerful vasodilator) and therefore has a potential role in heart health and circulation (5).
Up to 6g daily of L-ornithine or L-arginine has been used safely on a short-term basis, and up to 40g has been administered as a one-off without side effects. However 500-2000 mg is the normally accepted level for safe self-administration.
INTERACTIONS AND CONTRA-INDICATIONS
L-arginine supplements should be avoided by those that have a tendency to suffer from herpes simplex (cold sores), as this amino acid can exacerbate the condition. (Consumption of L-arginine rich foods such as chocolate, milk, meat, cheese, nuts, popcorn and peas should be reduced as well).
L-ornithine does not have the same stimulating effect on herpes simplex.
Neither L-ornithine nor L-arginine should be taken by schizophrenics.
N.B. L-ornithine is an unstable nutrient and has to be present in the form of L-ornithine hydrochloride (HCl) in supplements.
1. Gebhardt R, et al. Treatment of cirrhotic rats with L-ornithine-L-aspartate enhances urea synthesis and lowers serum ammonia levels. .J Pharmacol Exp Ther, 283;1:1-6 1997.
2. The Healing Nutrients Within, E R Braverman & C C Pfeiffer, Keats, 1987.
3. Ulland AE, et al. Altered Wound arginine metabolism by corticosterone and retinoic acid. J Surg Res, 70;1:84-88 1997.
4. Albina JE, Abate JA, Mastrofrancesco B. Role of ornithine as a proline precursor in healing wounds. J Surg Res, 55;1:97-102 1993.
5. Chowienczyk P, Ritter J. Arginine: NO more than a simple aminoacid? The Lancet, 350;9082:901-902 1997.