Citrulline

Citrulline is a non-protein amino acid generated in the urea cycle and as a by-product of nitric oxide (NO) synthesis from arginine, and an efficient precursor for endogenous arginine and NO regeneration. Salivary citrulline reflects NO-pathway flux and ammonia handling relevant to vasodilation, substrate delivery, and fatigue resistance during exercise. Gonzalez and Trexler (2020) reviewed citrulline's role in enhancing NO bioavailability and exercise performance.