L-NMMA (citrate) is a relatively non-selective inhibitor of all NOS isoforms [1].
Nitric oxide synthases (NOSs) belong to a family of enzymes involved in catalyzing the production of nitric oxide (NO) from L-arginine. As an important cellular signaling molecule, NO has been implicated in modulating vascular tone, insulin secretion, airway tone, and peristalsis, angiogenesis and neural development. Until now, three isozymes of NOS have been identified: eNOS (endothelial NOS), nNOS (neuronal NOS), and iNOS (inducible NOS). The eNOS plays a critical role in embryonic heart development and morphogenesis of coronary arteries and cardiac valves. The nNOS functions as a retrograde neurotransmitter important in long term potentiation and has been involved in the development of nervous system. The iNOS produces large amounts of NO as a defense mechanism and is an important factor in the response of the body to attack by parasites, bacterial infection, and tumor growth [2].
L-NMMA inhibited the activity of NOS with the Ki values of approximately 0.18, 0.4, and 6 μM for nNOS (rat), eNOS (human), and iNOS (mouse), respectively [1]. In perfused dog mesenteric artery segments, treatment with L-NMMA increased the vasoconstriction induced by adrenergic nerve stimulation. In dog cerebral artery strips, L-NMMA suppressed the relaxant response to transmural nerve stimulation [3]. In patients with cardiogenic shock, L-NMMA administration is safe and has favorable clinical and hemodynamic effects [4].
References:
[1] Frey C, Narayanan K, McMillan K, et al. L-thiocitrulline. A stereospecific, heme-binding inhibitor of nitric-oxide synthases[J]. Journal of Biological Chemistry, 1994, 269(42): 26083-26091.
[2] Stuehr D J, Griffith O W. Mammalian nitric oxide synthases[J]. Advances in Enzymology and Related Areas of Molecular Biology, Volume 65, 2006: 287-346.
[3] TODA N, OKAMURA T. Modification by L-NG-monomethyl arginine (L-NMMA) of the response to nerve stimulation in isolated dog mesenteric and cerebral arteries[J]. The Japanese Journal of Pharmacology, 1990, 52(1): 170-173.
[4] Cotter G, Kaluski E, Blatt A, et al. L-NMMA (a nitric oxide synthase inhibitor) is effective in the treatment of cardiogenic shock[J]. Circulation, 2000, 101(12): 1358-1361.