N-Methylarginine is an inhibitor of nitric oxide synthase.[1][2] Chemically, it is a methyl derivative of the amino acid arginine. It is used as a biochemical tool in the study of physiological role of nitric oxide.
The inhibiting effect of N-methylarginine on vasodilation is lower in hypertensive patients than in normal subjects, indicating endothelial dysfunction.[3] The inhibiting effect of N-methylarginine on vasodilation declines progressively with age, but has been restored with vitamin C in the oldest subjects.[3]
Up to the age of 60 years, despite the evident decline in endothelium-dependent vasodilation, vitamin C did not modify the response to acetylcholine. In contrast, in the oldest individuals (age >60 years) characterized by a profound alteration in NO availability, vitamin C not only enhanced the response to the endothelial agonist but also restored the inhibiting effect of L-NMMA on vasodilation to acetylcholine.