Arginine is a non-essential amino acid that the body can produce in the liver. In times of stress or injuries arginine becomes an essential amino acid. Arginine occurs naturally in the L(+) form, available as the glutamate and hydrochloride. . Arginine is vital for the production of protein. Only the L form of amino acids are constituents of protein. Arginine crosses the blood-brain barrier, is a precursor for nitric oxide and is responsible for the secretion of hormones such as growth hormone,