Inhibition of nitric oxide synthesis by N^G‐nitro‐L‐arginine methyl ester (L‐NAME): requirement for bioactivation to the free acid, N^G‐nitro‐L‐arginine

Abstract

1 The L-arginine derivatives N0-nitro-L-arginine (L-NOARG) and NG-nitro-L-arginine methyl ester (L-NAME) have been widely used to inhibit constitutive NO synthase (NOS) in different biological systems. This work was carried out to investigate whether L-NAME is a direct inhibitor of NOS or requires preceding hydrolytic bioactivation to L-NOARG for inhibition of the enzyme. 2 A bolus of L-NAME and L-NOARG (0.25 Mmol) increased coronary perfusion pressure of rat isolated hearts to the same extent (21 +0.8 mmHg; n = 5), but the effect developed more rapidly following addition of L-NOARG than L-NAME (mean half-time: 0.7 vs. 4.2 min). The time-dependent onset of the inhibitory effect of L-NAME was paralleled by the appearance of L-NOARG in the coronary effluent. 3 Freshly dissolved L-NAME was a 50 fold less potent inhibitor of purified brain NOS (mean IC50 = 70 gM) than L-NOARG (IC50= 1.4 giM), but the apparent inhibitory potency of L-NAME approached that of L-NOARG upon prolonged incubation at neutral or alkaline pH. H.p.l.c. analyses revealed that NOS inhibition by L-NAME closely correlated with hydrolysis of the drug to L-NOARG. 4 Freshly dissolved L-NAME contained 2% of L-NOARG and was hydrolyzed with a half-life of 365 + 11.2 min in buffer (pH 7.4), 207 ± 1.7 min in human plasma, and 29 + 2.2 min in whole blood (n = 3 in each case). When L-NAME was preincubated in plasma or buffer, inhibition of NOS was proportional to formation of L-NOARG, but in blood the inhibition was much less than expected from the rates of L-NAME hydrolysis. This was explained by accumulation of L-NOARG in blood cells. 5 These results suggest that L-NAME represents a prodrug lacking NOS inhibitory activity unless it is hydrolyzed to L-NOARG. Bioactivation of L-NAME proceeds at moderate rates in physiological buffers, but is markedly accelerated in tissues such as blood or vascular endothelium.

Endothelium-Dependent Relaxation in Pulmonary Arteries of L-NAME-Treated Wistar and Stroke-Prone Spontaneously Hypertensive Rats.

“…L-NAME has been shown to inhibit the synthesis of NO in the endothelium (Rees et al, 1990;Pfeiffer et al, 1996), and such inhibition has been reported to enhance vascular smooth muscle contraction (Martin et al, 1986;Alosachie and Godfraind, 1988;Osugi et al, 1990;Kaneko and Sunano, 1993). We have also observed that EDR of the aorta and of the carotid and iliac arteries from L-NAME-treated rats was impaired (Sekiguchi et al, 2001).…”

A role for asymmetric dimethylarginine in the pathophysiology of portal hypertension in rats with biliary cirrhosis†‡

“…The effect of ADMA was similar to that of L-NAME, a known inhibitor of NOS. 21 ADMA induced a decrease in NOx levels, suggesting that ADMA induces intrahepatic endothelial dysfunction by inhibiting NOS. When ADMA was administrated together with L-NAME, a synergistic increase in perfusion pressure-or paradoxical vasoconstriction-occurred, which was associated with a further decrease in NOx levels.…”

“…L-NAME is an inactive prodrug that upon hydrolization is bioactivated to N G -nitro-L-arginine, a direct inhibitor of NOS. 21 The response to cumulative doses of acetylcholine was expressed as percent change in perfusion pressure, as previously described. 5,7 Determination of Dimethylarginines and NOx.…”

NO Synthase Inhibition Increases Aldosterone in Humans

“…As in previous studies, the blood pressure effect persisted after discontinuation of L-NAME, consistent with conversion of L-NAME to a long-acting active metabolite L-N G -nitro-Larginine. 22 L-NAME decreased heart rate, most likely because of stimulation of the baroreflex. Interestingly, although 1 month of pretreatment with oral L-arginine attenuated the peak blood pressure response to L-NAME, it did not abolish this pressor response.…”