The amino acid L-arginine appears to reduce blood pressure and other risk factors for heart disease. The finding, reported in the current issue of the Journal of Clinical Investigation, may help explain why overweight people and some diabetics are at high risk for the disease.
The body converts L-arginine into nitric oxide, a potent chemical that helps regulate blood pressure. Probing this link further, Dario Giugliano and his colleagues at the Second University of Naples in Italy infused L-arginine into 10 healthy volunteers and kept track of several risk factors for cardiovascular disease: blood pressure, blood viscosity, and clumping of platelets--the cells that form blood clots. The researchers found that all three risk factors improved between 10% and 20% in response to the amino acid, and the subjects' heart rates and blood flow in their legs increased. When the scientists repeated the experiment but blocked the subjects' production of the hormone insulin, which controls blood-sugar levels, L-arginine's beneficial effects were reduced by half. When they infused insulin along with the amino acid, the effects were restored.
The study is the first to show that insulin enhances L-arginine's effects in people, Giugliano says, and it may help explain why overweight diabetics--who often have faulty insulin receptors--are also at risk for cardiovascular disease. But not all researchers are convinced of the link. "They show an interesting phenomenon," says Michael Quon, who studies the connections between insulin, nitric oxide, and L-arginine at the National Heart, Lung, and Blood Institute in Bethesda, Maryland. "But the effect is small."