Acute ingestion of 6 g or 12 g citrulline malate does not significantly improve flow-mediated dilation of the brachial artery in healthy young males at rest within 120 minutes, despite increasing serum concentrations of citrulline, arginine, and ornithine.

When citrulline is taken by mouth, it turns into arginine in the kidneys, and arginine is used by blood vessel lining cells to make nitric oxide. Nitric oxide tells the muscle around blood vessels to relax, which should make the vessels wider. But even though more arginine and nitric oxide precursors are present, the blood vessels do not get wider in healthy young men at rest, because the system is already operating at its maximum capacity and cannot respond further without additional demand like exercise.