Arginine is a precursor for nitric oxide, which has been shown to lower blood pressure, reduce blood clotting and protect against myocardial infarction and strokes.
Researchers from the ARS, Texas A&M University, the University of Nevada, and Oklahoma State University, have reported that blood arginine levels increased by 22 per cent after three weeks of drinking watermelon juice with every meal.
“Some studies have reported that high oral doses of arginine were associated with nausea, gastrointestinal discomfort, and diarrhoea in humans. A solution to this potentially severe problem may be the alternative use of l-citrulline, an effective precursor for arginine synthesis,” explained lead author Julie Collins in the journal Nutrition.
Indeed, L-citrulline is a neutral amine acid, meaning it does not compete with basic amino acids for transport by cells. Conversion of L-citrulline to arginine consumes ammonia, said Collins, meaning the amino acid could be useful for people with elevated ammonia levels, arginine transport problems, or enhanced intestinal arginine breakdown, as is found in people with stress and infection.
The researchers recruited healthy volunteers (between 12 and 23 per intervention group) and assigned them to receive 0, 780, or 1560 grams of watermelon juice per day, providing a daily L-citrulline dose of 0, 1 or 2 grams. The interventions lasted three weeks and subjects were later crossed over after washout periods of two to four weeks.
Arginine plays an important role in cell division, the healing of wounds, removing ammonia from the body, immune function, and the release of hormones. Arginine, taken in combination with pycnogenol or yohimbine, has also been reported to improve erectile dysfunction significantly.
The geometry, charge distribution and ability to form multiple H-bonds make arginine ideal for binding negatively charged groups. For this reason arginine prefers to be on the outside of the proteins where it can interact with the polar environment. Incorporated in proteins, arginine can also be converted to citrulline by PAD enzymes. In addition, arginine can be methylated by protein methyltransferases.
As a precursor
Arginine is the immediate precursor of NO, urea, ornithine and agmatine; is necessary for the synthesis of creatine; and can be used for the synthesis of polyamines (mainly through ornithine and to a lesser degree through agmatine), citrulline, and glutamate. For being a precursor of NO, (relaxes blood vessels), arginine is used in many conditions where vasodilation is required. The presence of asymmetric dimethylarginine (ADMA), a close relative, inhibits the nitric oxide reaction; therefore, ADMA is considered a marker for vascular disease, just as L-arginine is considered a sign of a healthy endothelium.