GPLC increases nitric oxide levels in bodybuilders

Nitric oxide (NO) is a chemical secreted by the inner lining of blood vessels that helps control blood flow in muscles and other types of tissue (e.g. the penis). An increase in nitric oxide release could improve blood flow to muscles during exercise in bodybuilders. Some athletes use supplements designed to increase nitric oxide production, but these products have no proven benefits to date.
A study conducted at the University of Memphis under the direction of Richard Bloomer showed that Glycine-propionyl-L-carnitine (GPLC) supplements (GlycoCarn: 3 grams per day in combination with 1,044 milligrams of glycine over four weeks) increased nitric oxide production in men training with weights. The scientists restricted the blood supply to the arm using a cuff for 6 minutes and then released the cuff. This caused a reflex increase in muscle blood flow to the arm, which was partly due to nitric oxide release through the blood vessels. Blood samples taken after the cuff was released showed that nitric oxide levels (as measured by the indirect markers nitrite and nitrate) were highest when GPLC was ingested. We do not know whether increasing nitric oxide levels promotes muscle growth in bodybuilders.
(Journal International Society Sports Nutrition, 4: 22, 2007, published online)