The nitric oxide precursor L-arginine reduces expression of hyaluronan synthase in experimental vein bypass grafts.

BACKGROUND: The success of vascular bypass procedures is limited by the development of intimal hyperplasia (IH). The nitric oxide (NO) precursor, L-arginine (L-ARG) significantly reduces IH in both arteries and experimental vein grafts; however, the precise mechanism has yet to be elucidated. Hyaluronan synthase-1 (HAS-1) is one of the two enzymes believed to be responsible for making hyaluronan, a key component extracellular matrix composition. PURPOSE: To determine how L-ARG supplementation affects the gene expression of HAS-1 in experimental vein grafts. METHODS: Thirty-four male New Zealand white rabbits were divided into three groups: control (no operation, regular chow and water, n = 4); L-ARG supplemented (n = 15); and no L-ARG (n = 15). The latter two groups underwent a right interposition carotid bypass using jugular vein. Vein grafts were harvested at 7, 14, and 21 days after surgery. Ribonuclease protection assays were performed using 32P-labeled riboprobes for HAS-1 and 18S rRNA as an internal control and expressed as a ratio (HAS-1/rRNA). RESULTS: There was a significant rise in HAS-1 expression in the vein grafts 7 (1.57 +/- 0.5), 14 (0.7 +/- 0.2), and 21 days (2.82 +/- 0.7) after grafting compared to control (0.14 +/- 0.08) (P < 0.05). L-ARG-supplemented animals had a significant decrease in HAS-1 expression at 21 days (0.65 +/- 0.1) compared to nonsupplemented vein grafts (2.82 +/- 0.7) (P < 0.02). CONCLUSIONS: These results demonstrate for the first time a significant rise in HAS expression in the early experimental vein grafts. Furthermore, L-ARG supplementation significantly diminishes the expression of HAS at 21 days. These results may represent a potential mechanism by which augmentation of the L-ARG/NO pathway inhibits IH in experimental vein grafts and may ultimately provide for improved therapeutic interventions in alleviating IH.

Reduction of experimental vein graft intimal hyperplasia and preservation of nitric oxide-mediated relaxation by the nitric oxide precursor L-arginine.

BACKGROUND: Previous studies in animals and human beings have shown that vein bypass grafts exhibit diminished endothelium-dependent relaxation and the development of intimal hyperplasia. This study examines the effect of L-arginine on experimental vein graft endothelial cell function and the development of intimal hyperplasia. METHODS: Common carotid vein bypass grafts were performed in 24 New Zealand White rabbits: 12 were controls and 12 received L-arginine (2.25%) orally 7 days before operation and thereafter until harvest 28 days after operation. Intimal and medial dimensions were determined by planimetry on pressure-fixed vessels. Relaxation to acetylcholine, serotonin, calcium ionophore (A23187), and sodium nitroprusside was performed on precontracted vessel rings. RESULTS: Arginine-treated vein grafts showed a 47% reduction in mean intimal thickness (p < 0.001) compared with controls. By scanning and transmission electron microscopy, all vein grafts showed a confluent endothelium. In contrast to control grafts, which do not relax to acetylcholine and serotonin, arginine-treated vein grafts relaxed in response to both agonists. There was a significant increase (p < 0.05) in the maximal relaxation to calcium ionophore (A23187) in arginine-treated vein grafts compared with control grafts. Non-endothelium-dependent responses to sodium nitroprusside were equivalent in all vein grafts. CONCLUSIONS: This study shows that oral L-arginine supplementation significantly reduces intimal hyperplasia and preserves nitric oxide-mediated relaxation in experimental vein grafts, suggesting a role for nitric oxide in the regulation of the cellular events that lead to intimal hyperplasia.

L-arginine improves endothelium-dependent vasorelaxation and reduces intimal hyperplasia after balloon angioplasty.

Reductions in nitric oxide (NO) activity persist after arterial intimal injury and may be a factor in the development of intimal hyperplasia. NO inhibits in vitro platelet aggregation, leukocyte adhesion, and smooth muscle cell growth, all of which are key components in the process of intimal hyperplasia. We hypothesized that long-term supplementation with L-arginine, the precursor of NO, would increase NO production and thereby improve endothelium-dependent vasorelaxation and simultaneously reduce intimal hyperplasia. Twenty-six New Zealand White male rabbits were fed standard rabbit chow either with or without 2.25% L-arginine in their drinking water for 3 weeks. Then the animals underwent unilateral iliac artery angioplasty and were continued on their respective diets. Four weeks after angioplasty, the iliac arteries were harvested for functional and morphometric studies. The iliac arteries from several animals from each group were processed for study by electron microscopy. Maximal endothelium-dependent vasorelaxation in injured arteries was significantly greater in L-arginine-supplemented animals (mean +/- SEM, 71.8 +/- 4.1%; n = 6) than controls (51.4 +/- 4.0%, n = 7; P < .05). Furthermore, the intimal area in injured arteries was significantly reduced in L-arginine-supplemented animals (0.22 +/- 0.03 mm2, n = 5) compared with controls (0.34 +/- 0.03 mm2, n = 6; P < .05). These data suggest that L-arginine supplementation enhances NO production at sites of vascular healing and may reduce intimal hyperplasia.

Heparin prevents postischemic endothelial cell dysfunction by a mechanism independent of its anticoagulant activity.

PURPOSE: Heparin may have protective effects on postischemic vascular endothelial cell function that are distinct from its anticoagulant, antiplatelet, or anticomplement activity. We tested this hypothesis in isolated rat hindlimbs. METHODS: Isolated rat hindlimbs underwent 60 minutes of normothermic ischemia and 10 minutes of reperfusion. Potential heparin interaction with plasma-based proteins or cells was eliminated by perfusion of the hindlimbs with a nonrecirculated albumin-enriched crystalloid buffer. Endothelial function was assessed by measurement of endothelium-derived relaxing factor (EDRF) activity. Limbs perfused at constant pressure were subjected to increasing log dose infusions of acetylcholine and nitroprusside to measure endothelial-dependent (EDRF-mediated) and endothelial-independent vasoreactivity, respectively. Fifty limbs were divided into seven groups: two nonischemic groups (one with heparin) and five ischemia/reperfusion groups treated with increasing doses of heparin (0 to 1.0 U/ml perfusate). RESULTS: The nontreated ischemia/reperfusion group (n = 12) had a 46.2% reduction in endothelial-dependent vasodilation of the rat hindlimb when compared with the nonischemic control (n = 7, p < 0.05). Treatment with heparin 0.5 U/ml (n = 6) nearly abolished this attenuation of endothelial-dependent vasodilation (4.3% reduction, p = not significant vs nonischemic control). The endothelial protective effect of heparin was dose-dependent: groups treated with 0.25 U/ml (n = 6) and 0.1 U/ml heparin (n = 7) showed progressive impairment in postischemic EDRF-mediated vasodilation. Endothelial-independent vasodilation induced by nitroprusside was unchanged by ischemia/reperfusion or heparin treatment, which confirmed that the postischemic damage and its protection by heparin were specific to the endothelium. CONCLUSIONS: Heparin prevented postischemic endothelial cell dysfunction by a mechanism independent of its interactions with plasma-based proteins or cells. This nonanticoagulant protective effect may contribute to the salutary effects of heparinization during acute ischemic events.