L-Citrulline / Citrulline is an amino acid that supports the body in optimizing blood flow through its conversion to L-arginine and then nitric oxide. Nitric oxide is involved in vasodilatation, and low levels are associated with mental and physical fatigue and sexual dysfunction.Citrulline, which is considered a non-essential amino acid synthesized in the intestinal tract from Glutamine, converts to Arginine in the endothelial cells. This biochemical process involves L-Aspartate and the enzymes Argininosuccinate Synthetase and Argininosuccinate Lyase, in the presence of ATP. Arginine is important for Nitric Oxide production for cardiovascular health; however, most Arginine is utilized in the liver and kidneys, and only a fraction is available for this purpose. Since Citrulline is a precursor to Arginine, it allows for increased and sustained Nitric Oxide production in the endothelium for support of circulatory function.