L-arginine is an essential amino acid found naturally in meat, dairy, poultry and fish, It is also available as an herbal supplement and is often marketed as a 'natural Viagra'.
Nitric oxide (NO) is produced by all tissues in the body and plays a crucial role in smooth muscle relaxation. NO is formed from L-arginine using the enzyme nitric oxide synthetase (NOS).
It is well known that ED is commonly found in men with ischaemic heart disease. Vasculogenic ED may be a manifestation of atherosclerosis, and thus the L-arginine-NO pathway is hypothesized as an explanation for the association. There are only a few human studies evaluating the role of L-arginine in ED, and these have yielded mixed results.
One study investigated the effects of L-arginine in 32 patients (mean age 51.6 years) with mixed-type ED in a randomized, placebo-controlled, crossover trial . Patients were administered 3 x 500 mg L-arginine/d or placebo for two 17-d courses. After a 7-d washout period, patients who initially received the placebo for 17 d were switched to L-arginine and vice versa.
Five patients (17%) reported a significant improvement in their sexual performance as measured by a validated questionnaire after the L-arginine phase, compared to 6 patients (20%) who reported a benefit after the placebo period. There was no statistically significant difference between improvements with L-arginine compared to placebo (56% vs. 43%). They concluded that L-arginine at 3 x 500 mg per day dose was no better for ED than placebo .
Other studies have shown positive results but have tended to use larger doses of L-arginine. One group conducted a double-blind trial in 50 men with ED . Patients were given L-arginine (5 g per day) or a matching placebo for 6 weeks.
At the end of the study, 9 of the 29 arginine group reported a significant subjective improvement compared to only 2 of the 17 placebo group .
Another study administered Pycnogenol orally, which is known to increase the production of NO by stimulating activity of NOS, together with L-arginine as a substrate for NOS .
The group consisted of 40 men with ED who were given three ampoules of Sargenor a day for the first month. This is a drinkable solution of the dipeptide arginyl aspartate (equivalent to 1.7 g of L-arginine per day). During the second month, patients were additionally supplemented with 40 mg of Pycnogenol twice a day, and during the third month the daily dosage was increased to three 40-mg Pycnogenol tablets.
At the end of the first month with L-arginine alone, a statistically non-significant number of 2 patients (5%) experienced a normal erection. At the end of the second month of receiving a combination of L-arginine and Pycnogenol, the number of men with restored sexual ability increased to 80%. After the 3-month trial period, 92.5% of the men experienced a normal erection. These men also experienced a decrease in time for an erection to develop after stimulation and an extended duration of erection. The authors concluded that oral administration of L-arginine in combination with Pycnogenol causes a significant improvement in sexual function in men with ED without any side effects .
Although none of the studies reported side effects of receiving regular L-arginine, high doses of the drug can stimulate the production of gastrin, resulting in increased gastric acid production. Hence, it may cause gastro-intestinal problems and has been reported to induce necrotizing pancreatitis in rats .
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