NG-nitro L-arginine methyl ester and other alkyl esters of arginine are muscarinic receptor antagonists.

Abstract

Analogues of L-arginine with modifications at the terminal guanidino nitrogen and/or the carboxyl terminus of the molecule have been widely used for their ability to inhibit the production of nitric oxide and are thought to be competitive antagonists of nitric oxide synthase. The present studies were designed to test the possibility that these agents are also muscarinic receptor antagonists. Acetylcholine produced concentration-dependent contraction of endothelium-denuded rabbit coronary artery as well as isolated strips of canine colonic smooth muscle. The arginine analogue NG-nitro L-arginine methyl ester (L-NAME, 100 p,M) but not NG-monomethyl L-arginine (L-NMMA, 100 ,uM) significantly shifted these contractile relations to the right, an effect that was not reversed by addition of 1 mM L-arginine. In radioligand binding studies using the muscarinic radioligand [3H]quinuclidinyl benzilate and tissues known to contain differing contributions of Ml, M2, and M3 muscarinic receptors, addition of increasing concentrations of L-NAME resulted in a monophasic competition of binding with affinities (K1) ranging from 68 juM in endothelium to 317 ,M in whole aorta. Addition of the hydrolysis-resistant guanosine 5'-triphosphate analogue GTPyS (100 gM) had no effect on L-NAME competition of [3H]quinuclidinyl benzilate binding. Addition of L-NAME in radioligand binding competition studies using the agonist carbachol did not result in an alteration of the receptor's affinity for agonist, confirming the competitive nature of the interaction of L-NAME with the muscarinic receptor. Several L-arginine analogues with alkyl ester modifications at the carboxyl end of the molecule as well as those without this modification were evaluated as muscarinic antagonists in radioligand binding experiments. Only those arginine compounds with a modified carboxyl group were able to compete for radioligand binding to the muscarinic receptor. Our results indicate that alkyl esters of L-arginine are muscarinic antagonists and suggest that these compounds are poor choices as nitric oxide synthase inhibitors in studies in which muscarinic receptors are not blocked. (Circulation Research 1993;72:387-395 macrophages and may play a role in signaling in the immune system.2Numerous congeners of arginine that block the action of nitric oxide synthetase (NOS) in several tissues including endothelium, nerve, and smooth muscle have been described.2 The simplest of these compounds, N0-nitro L-arginine (L-NA), is an inhibitor of NOS both in vivo and in vitro5 and is widely used as its methyl ester analogue NG-nitro L-arginine methyl ester (L-NAME), which is more lipophilic and therefore useful for experiments in vivo.6 In studies designed to elucidate the role of NO in the gastrointestinal tract, an inhibitory effect of L-NAME on cholinergic neural responses was sometimes observed. This inhibitory effect would be consistent with an action of L-NAME at the muscarinic receptor. Indeed, although differences in the actions of NOS inhibitors such as L-NAME in vivo...

Nitric oxide modulation of the hypothalamo-neurohypophyseal system

“…Similar results are observed when the availability of NO is reduced by the NO scavenger, carboxy PTIO (Summy-Long JY and Bui V, unpublished data). This is an important comparison to interpret NO's effects on hormone secretion because it has been shown that, in addition to inhibiting NOS activity, L-NAME also has antimuscarinic effects (30). Thus, our studies indicate that NO is tonically produced in the forebrain during euvolemic isosmotic conditions to inhibit secretion of both hormones from the magnocellular system.…”

Blockade of Nitric Oxide Synthesis Inhibits Hippocampal Hyperemia in Kainic Acid-Induced Seizures

“…Before reaching conclusions about the role of NO in the cerebrovascular reactions under study, some discussion about the effects of L-NAME not attributable to NOS inhibition is needed, since L-NAME has been shown to be a muscarinic antag onist (Buxton et a!., 1993). However, the seizures induced by KA mostly involve glutamatergic path ways rather than cholinergic pathways, and in the present experiments, the seizure intensity (electro graphic and behavioral events) was not reduced by L-NAME.…”

Asymmetric Dimethylarginine Produces Vascular Lesions in Endothelial Nitric Oxide Synthase–Deficient Mice

“…14 It is therefore possible that nonspecific vascular effects may not be limited to ADMA in particular but may also be extended to L-arginine analogues in general. Multiple actions of L-arginine analogues have been reported, which include inhibition of cytochrome c reduction, 13 endothelial generation of superoxide anions, 40 antagonism of muscarinic acetylcholine receptors, 12 impairment of urea cycle in which L-arginine is a substrate, 41 and inhibition of the endothelium-independent relaxation induced by amiloride (an inhibitor of Na ϩ -H ϩ exchange) and dibutyryl cAMP (a membranepermeable cAMP analogue). 42 Thus, multiple mechanisms other than simple inhibition of endothelial NO synthesis appear to be involved in the long-term vascular effects of L-arginine analogues.…”

“…8,9 See cover However, it is controversial whether these vascular effects of L-NAME are caused primarily by the inhibition of endothelial NO synthesis for the following reasons: first, the importance of endothelium-derived NO decreases as the vessel size becomes smaller, 10 whereas L-NAME-induced vascular lesions are prominent at microvascular levels; 8 second, long-term treatment with L-NAME does not reduce eNOS activity; 11 third, multiple actions of L-NAME other than simple inhibition of NO synthesis have been reported. 12,13 The most appropriate way to address this issue is to use mice that are deficient in the eNOS gene and to examine whether long-term treatment with L-NAME causes coronary vascular lesions in those mice. We have recently shown that treatment with L-NAME causes a comparable extent of coronary arteriosclerotic lesions in wild-type and eNOS-KO mice.…”