硝基酪氨酸对大鼠α-肾上腺素能受体介导血管反应性的影响

Effect of nitrotyrosine on α-adrenergic receptor-mediated vascular reactivity in rats

目的 观察硝基酪氨酸(3-NT)对α-肾上腺素能受体介导血管反应性的影响并探讨其机制。方法 雄性 SD 大鼠24只，随机分成对照组(n=12)和3-NT 组(n=12)。两组动物分别于注入生理盐水和3-NT(2.5μmol·kg^(-1))30、90min 后，静脉注射α_1-肾上腺素能受体激动剂苯肾上腺素(PE)0.5～2.5μg·kg^(-1)和垂体加压素1.3～5.2μg·kg^(-1)，记录注药后平均动脉压(MAP)的增幅百分比。另取6只健康雄性 SD 大鼠胸主动脉环置于 Krebs Ringer 液中，先以累加给药方式给予 PE1×10^(-9)～3×10^(-5)μmol 建立 PE 的剂量-反应曲线；5次清洗后，将标本随机对半分为重复对照组(Krebs Ringer液)和3-NT组(含有250μmol3-NT Krebs Ringer 液)孵化60min，然后重复上述 PE 激发的血管收缩反应。结果 与对照组相比，PE 增高大鼠 MAP 的作用可被3-NT 抑制，且与时间有关，而对垂体加压素引起的 MAP 增高没有影响。在血管环张力实验中，对照组及3-NT 组对 PE 的浓度反应曲线和 Emax、EC50均无显著性差异。结论 3-NT 选择性抑制α-肾上腺素能受体介导的血管反应，但这种作用似乎与竞争性拮抗α-肾上腺素能受体无关，提示3-NT 可能通过其他未知的途径干扰α-肾上腺素能受体介导的血管反应性。

Objective3-nitro-L-tyrosine(3-NT)has been shown to be the marker of ONOO-productionin the tissue during septic shock.We aimed to investigate the effects of 3-NT on adrenergic receptor-mediatedvascular reactivity and the possible mechanism.Methods The experiment consisted of two parts.In part Ⅰ twenty-four male SD rats weighing 200-300g were anesthetized with intraperitoneal pentobarbital 40 mg·kg^(-1).Spontaneousbreathing was maintained.The animals were randomly divided into 2 groups:A control group received normalsaline i.v.(n=12)and B 3-NT group received 3-NT 2.5 μmol·kg^(-1) i.v.(n=12).30 min and 90 min after 3-NT/N.S.administration the animals received i.v.phenylephrine(PE)0.5,1.0,1.5,2.0,2.5 μg·kg^(-1)(subgroup Ⅰ)or vasopressin 1.3,2.6,3.9,5.2 μg·kg^(-1)(subgroup Ⅱ)at 15 min intervals.The percentageincrease in MAP was recorded.In part Ⅱ six male SD rats were anesthetized and killed.The thoracic aorta wasimmediately removed and aortic rings of 3 cm in length were prepared and suspended in Krebs-Hensleit solutionmaintained at 37℃ and aerated with 95% O_2 and 5% CO_2 and prestretched with a load of 2g.Before theexperiment the response of the aortic tings to cumulative addition of PE(1×10^(-9)-3×10^(-5)mol)was prelimarilymeasured.Alter five washes the aortic rings were randomly divided into 2 groups:control group(KH solution)and 3-NT group(KH solution containing 3-NT 250 μmol·L^(-1)).After 60 min incubation,response to PE wasmeasured in both groups and concentration-response curve was obtained and Emax and CE_50 were calculated.Results PE increased MAP in a dose-dependent manner.PE 2.5 μg·kg^(-1) increased MAP by 20% of thebaseline value.30 and 90 min after 3-NT 2.5 μmol·kg^(-1) the hypertensive response of the animal to PE wassignificantly inhibited but 3-NT did not affect the increase in MAP induced by vasopressin.In the isolated SD rataortic ring experiment there was no significant difference in the concentration-response curve and Emax and EC50values of PE between the 3-NT and control group.Conclusion 3-NT selectively inhibits α-adrenoceptor mediatedhemodynamic response through mechanisms other than competitively antagonizing α-adrenoceptor.