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 th e coronary artery endothelium. L-Arginine is the endogenous substrate for production of NO via the NO synthase pathway. This study tested th e 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 ant erior descending (LAD) coronary artery segments were isolated from nor mal, anesthetised (30 mg/kg i.v. pentobarbitone) dogs. LAD segments we re either cut into 2-3 mm rings and mounted in organ chambers to measu re vascular tone responses to acetylcholine (endothelium-receptor-depe ndent) and acidified NaNO2 (smooth muscle), or cut into segments to me asure adherence of fluorescently labeled neutrophils by epifluorescenc e microscopy. Results: L-Arg had no direct inhibitory effect on O-2(-) production (cytochrome c reduction) by PMN activated with platelet ac tivating 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-arg inine, (D-Arg, 10 mmol) did not reduce adherence (162 +/- 20 PMN/mm(2) ). To determine the effect of PMN on coronary artery endothelial funct ion, canine coronary artery rings were transiently incubated with acti vated PMNs in organ chambers to induce dysfunction. After washout of P MN, the EC(50) (- log M) derived from post-injury concentration-relaxa tion responses to acetylcholine was significantly less in 10 mmol L-Ar g (6.94 +/- 0.08) than untreated rings (6.47 +/- 0.06). In contrast, 1 0 mmol D-Arg could not reverse this dysfunction (6.48 +/- 0.11). Concl usions: L-Arg reduces PMN-induced coronary endothelial dysfunction by inhibition of adherence via the L-arginine-NO pathway.