Figure 1. Schematic representation of the l-arginine pathway in the cutaneous vasculature.

l-Arginine (l-Arg) is the common substrate for both nitric oxide synthase (NOS) and arginase. Arginase catalyses the conversion of l-Arg to urea and l-ornithine, which is the precursor to proline and is important in cell growth and repair. NOS catalyses the conversion of l-Arg to l-citrulline and nitric oxide (NO). NO is required for full expression of reflex cutaneous vasodilatation.