From everything I read, L-citrulline is the way to go. It is one of three amino acids in the urea cycle along with L-arginine and L-ornithine. It is often used as a sports performance enhancer and cardiovascular health supplement. It results in less fatigue and improves endurance for aerobic and anaerobic exercise.
It also has benefits for men seeking relief from erectile dysfunction, especially if caused by or in conjunction with high blood pressure. Apparently after consumption L-citrulline is converted into arginine in the kidneys. Taking L-arginine alone provides a spike of L-arginine in the plasma while supplemental L-citrulline provides this benefit over a longer period of time.
While supplementing with high doses of L-arginine and L-orthithine can cause diarrhea, taking L-citrulline does not have this side effect and increases plasma levels of all three amino acids. For ED and circulatory benefits taking 3000 mg daily has shown great improvement.
Citrulline can be purchased in tablets, or in powder form from a variety of on-line companies and apparently is relatively safe without side effects in reasonable doses.
Watermelon is a good food source of Citrulline. Other food sources include cantaloupe, cucumbers, eggs, milk fish, nuts and red meat.
SEE LINKS for more detailed information:
ONE LAST LINK AND PERHAPS THE BEST EXPLANATION I HAVE SEEN ON CITRULLINE, HEART DISEASE AND ED IN MEN. YOU CAN OPEN LINK AND READ IT IN ITS ENTIRETY BELOW: