L-Arganine - L-arginine is an amino acid naturally found in red meat, poultry, fish, and dairy. It is necessary for making proteins and is commonly used for circulation. L-arginine is converted in the body into a chemical called nitric oxide. Nitric oxide causes blood vessels to open wider for improved blood flow. L-arginine also stimulates the release of growth hormone, insulin, and other substances in the body. L-arginine can help increase muscle mass and boost endurance.