Arginine is a “semi-essential” amino acid, which means that its endogenous synthesis is mostly sufficient to meet physiological demands.
The average dietary intake of Arginine is 5-7 g/day. However, under certain conditions, such as periods of traumatic or metabolic stress, the production of arginine might be insufficient to meet physiological demands.
Arginine is involved in the production of several enzymes, hormones and structural proteins, and is also involved in the synthesis of Growth Hormone (GH), Insulin, Glucagon, and Prolactin. It is a component of the hormone vasopressin, synthesised by the pituitary gland, and is the physiological precursor of several biological compounds, such as Nitric Oxide, Polyamines, Proline, Glutamate, Creatine, Agmatine and Urea.
Arginine and the mechanism of action in sports:
1) Stimulates the secretion of hormones involved in growth and metabolism: insulin and growth hormone
• Inhibits the secretion of somatostatin, which exerts inhibitory effects on the secretion of Growth Hormone and Insulin and acts directly on the pituitary gland to stimulate the synthesis/secretion of GH, leading to a muscle mass increase.
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• The stimulation of GH synthesis also stimulates IGF-I synthesis in most tissues. Somatropin – together with IGF1 – exerts significant effects on carbohydrate metabolism and insulin sensitivity regulation. IGF-1 increases this sensitivity, promoting the transport of glucose into cells and its utilization essentially by muscle tissue, which in turn promotes hypoglycaemia. This means a greater use of glucose in the muscle.
• Directly stimulates the release of insulin by β-pancreatic cells. However, when this occurs, L-arginine increases the release of SST from δ-pancreatic cells, which leads to a suppression of insulin increase. Therefore, in addition to its vasodilator action, arginine increases glucose uptake into the musculoskeletal system and other peripheral tissues sensitive to insulin (action dependent on the NO synthase).
2) It is a precursor of Nitric Oxide
Arginine is converted to L-citrulline through the action of Nitric Oxide Synthase (NOS). The conversion of Arginine by NOS enzymes, produces Nitric Oxide as the most relevant by-product and Citrulline is considered a by-product. It is therefore a precursor of Nitric Oxide, and:
• Intervenes in GH secretion. The NO-producing enzyme is expressed in several tissues, including pituitary cells. Potent stimulators of GH secretion, such as GHRH, also exert their effects on somatotrophs through the induction of NOS activity and, consequently, NO production.
• Increases the influx of calcium into pituitary cells, which also contributes to GH secretion.
• NO is involved in important functions such as vasodilation. NO is a direct-acting vasodilator of the muscle. As such, it increases blood flow into muscle tissue, thereby increasing the transport capacity of essential nutrients such as glucose and oxygen for metabolism and protein synthesis, and improves the removal of waste from the body.
By Carla Santos, Pharmaceutical