L-arginine inhibits neutrophil adherence and coronary artery dysfunction

Nitric oxide (NO) attenuates neutrophil (PMN)-mediated damage, partly by inhibiting superoxide anion (O-2(-)) generation and adherence to the coronary artery endothelium. L-Arginine is the endogenous substrate for production of NO via the NO synthase pathway. This study tested the hypothesis that the endogenous NO precursor L-arginine (L-Arg) would reduce PMN-induced coronary artery dysfunction by attenuating O-2(-) production and neutrophil adherence. Methods: Neutrophils and left anterior descending (LAD) coronary artery segments were isolated from normal, anesthetised (30 mg/kg i.v. pentobarbitone) dogs. LAD segments were either cut into 2-3 mm rings and mounted in organ chambers to measure vascular tone responses to acetylcholine (endothelium-receptor-dependent) and acidified NaNO2 (smooth muscle), or cut into segments to measure adherence of fluorescently labeled neutrophils by epifluorescence microscopy. Results: L-Arg had no direct inhibitory effect on O-2(-) production (cytochrome c reduction) by PMN activated with platelet activating factor (PAF) (34.6 +/- 4.8 nmol vs. 34.2 +/- 4.1 nmol). L-Arg (10 mmol) reduced adherence of fluorescently labeled PMN to isolated canine coronary artery endothelium activated by 100 nM PAF from 187 +/- 11 to 41 +/- 6 PMN/mm(2), P < 0.05. This inhibition of adherence was reversed by N-<(omega)over bar>-nitro-L-arginine (L-NA, 1 mmol) (175 +/- 20 PMN/mm(2)) and by the NO scavenger, carboxy-PTIO (600 mu M, 157 +/- 23 PMN/mm(2)). D-arginine, the nonmetabolised enantiomer of L-arginine, (D-Arg, 10 mmol) did not reduce adherence (162 +/- 20 PMN/mm(2)). To determine the effect of PMN on coronary artery endothelial function, canine coronary artery rings were transiently incubated with activated PMNs in organ chambers to induce dysfunction. After washout of PMN, the EC(50) (- log M) derived from post-injury concentration-relaxation responses to acetylcholine was significantly less in 10 mmol L-Arg (6.94 +/- 0.08) than untreated rings (6.47 +/- 0.06). In contrast, 10 mmol D-Arg could not reverse this dysfunction (6.48 +/- 0.11). Conclusions: L-Arg reduces PMN-induced coronary endothelial dysfunction by inhibition of adherence via the L-arginine-NO pathway.