3-硝基酪氨酸在细菌内毒素诱导大鼠血管低反应性中的介导作用

目的：观察3-硝基酪氨酸（3-NT）对感染性休克大鼠血管低反应性的介导作用及抗氧化剂对此的治疗效果。 方法： 40只雄性SD大鼠随机分成空白对照组(n=10); LPS休克组（LPS 15 mg·kg-1 iv, n=10）; 尿酸(UA)治疗组（注射LPS 1 h后200 mg·kg-1 ip, n=10）; N-乙酰-5-甲氧基色胺（melatonin）治疗组（注射LPS 1 h后10 mg·kg-1 ip, n=10）。空白对照组及注射LPS 6 h后各组动物，静注去氧肾上腺素（PE, 0.5-2.5 μg·kg-1）,记录注药后MAP的增加百分比。所有in vivo实验结束后取大鼠胸主动脉环作张力实验,，建立PE的剂量-反应曲线并计算相应的Emax、EC50值。注射LPS 6 h后检测各组动物血浆丙二醛（MDA）、硝酸盐/亚硝酸盐（nitrate/nitrite）与3-NT的含量。 结果： 静脉注射PE后，休克组动物MAP的平均增长率与对照组相比显著降低至54.60%（P<0.01）；而UA组、melatonin组MAP对PE反应的增长率较之休克组分别增高了37.70%、40.03%(P<0.05)。休克组大鼠胸主动脉环对PE的反应［(Emax，35.30%±9.80%； EC50， (15.70±4.50)nmol/L］与对照组相比有显著差异［（Emax，100%； EC50， (4.71±2.04) nmol/L, P<0.05］，经UA、melatonin治疗后血管反应性有显著改善(P<0.05)。尿酸、N-乙酰-5-甲氧基色胺治疗组的血浆MDA、硝酸盐/亚硝酸盐和3-NT的浓度也明显低于休克组(P<0.05)。 结论： 3-NT是感染性休克血管低反应的重要介导因子，抗氧化剂通过清除氧自由基，减少脂质过氧化物的形成、抑制体内NO的过量合成及有效清除3-NT，从而改善α-肾上腺素能受体介导的血管低反应性，对临床感染性休克病人的治疗可能有积极作用。

Role of 3-nitrotynosine in Escherichia coli LPS-induced vascular hyporeactivity in rats

AIM: To observe the pathological role of 3-nitrotynosine (3-NT) on Escherichia coli LPS-induced vascular hyporeactivity in rats and the therapeutic effect of antioxidants. METHODS: Forty male SD rats weighting from 200 g to 250 g were randomly divided into four groups: the control group (n=10); LPS shock group (n=10); uric acid-treated group (n=10); melatonin-treated group (n=10). 6 h after LPS shock, phenylephrine (0.5-2.5 μg·kg-1) was applied intravenously to all groups and the percentage increase in MAP was detected, respectively. The concentration-response curve of aorta rings from all groups rats were obtained by cumulative addition of phenylephrine (PE), and PE Emax, EC50 were calculated. The concentrations of plasma malondialdehyde (MDA), nitrate/nitrite and 3-NT were assayed in all groups 6 h after LPS shock. RESULTS: The MAP level induced by PE significantly decreased to 54.60% in LPS shock rats compared with the control (P<0.05). However, PE induced MAP level increased 37.70% and 43.05% in uric acid and melatonin treated rats, respectively, compared with the LPS shock rats (P<0.05). The maximum response and EC50 to PE were significant reduced in LPS shock rats ［Emax, 35.30%±9.80%; EC50, (15.70±4.50)nmol/L］ compared with control group ［Emax, 100%; EC50, (4.71±2.04)nmol/L, P<0.05］; but the reactivity of aorta to PE was improved obviously in uric acid and melatonin treated groups (P<0.05). The plasma concentration of MDA, nitrate/nitrite and 3-NT were much lower in uric acid and melatonin groups than those in LPS shock group (P<0.05). CONCLUSIONS: 3-NT is an important pathological factor on vascular hyporeactivity in LPS shock. Antioxidants effectively improve α-adrenergic receptor-mediated vascular reactivity in LPS shock rats partially by removing lipid peroxidative production, reducing nitric oxide and 3-NT biosynthesis in LPS shock. These results suggest that antioxidants have potential beneficial therapeutic effect for septic shock patients.