Nonspecific blockade of vascular free radical signals by methylated arginine analogues

Abstract

Methylated arginine analogues are often used as probes of the effect of nitric oxide; however, their specificity is unclear and seems to be frequently overestimated. This study analyzed the effects of N Gmethyl-L-arginine (L-NMMA) on the endothelium-dependent release of vascular superoxide radicals triggered by increased flow. Plasma ascorbyl radical signals measured by direct electron paramagnetic resonance spectroscopy in 25 rabbits increased by 3.8 ± 0.7 nmol/l vs baseline (28.7 ± 1.4 nmol/l, P<0.001) in response to papaverineinduced flow increases of 121 ± 12%. In contrast, after similar papaverine-induced flow increases simultaneously with L-NMMA infusions, ascorbyl levels were not significantly changed compared to baseline. Similar results were obtained in isolated rabbit aortas perfused ex vivo with the spin trap α-phenyl-N-tert-butylnitrone (N = 22). However, in both preparations, this complete blockade was not reversed by co-infusion of excess L-arginine and was also obtained by N-methyl-D-arginine, thus indicating that it is not related to nitric oxide synthase. L-arginine alone was ineffective, as previously demonstrated for N G -methyl-L-arginine ester (L-NAME). In vitro, neither L-arginine nor its analogues scavenged superoxide radicals. This nonspecific activity of methylated arginine analogues underscores the need for careful controls in order to assess nitric oxide effects, particularly those related to interactions with active oxygen species.

Glucose uptake during contraction in isolated skeletal muscles from neuronal nitric oxide synthase μ knockout mice

“…It was reported that the vasoconstrictor effect of L-NMMA involved superoxide production (50, 60) via activation of cyclooxygenase with the resultant increased production of superoxide inactivating endothelium-derived relaxing factor (NO) (50). On the other hand, L-NMMA inhibited endotheliumdependent release of superoxide induced by increased blood flow (44). Any nonspecific effect of L-NMMA remains to be further established.…”

Mechanisms of β-adrenergic receptor–mediated venodilation in humans

“…Several mechanisms may be responsible for the L ‐NMMA–induced venodilation: First, activation of α 1 ‐adrenergic receptors stimulates the production of reactive oxygen species, 36 , 37 which contribute to vasoconstriction. Because L ‐NMMA is a scavenger of reactive oxygen species, 38 , 39 it could induce a reversal of venoconstriction. Second, the NO synthase inhibitors L ‐NMMA and N ω ‐nitro‐ L ‐arginine methyl ester ( L ‐NAME) are able to directly block the mammalian nicotinic acetylcholine receptor channels, 13 suggesting blunted in vivo activity of the sympathetic nerve terminals.…”