内毒素血症对新生鼠脑一氧化氮合酶表达的影响

Effect of endotoxemia on the expression of nitric oxide synthase in the brain of neonatal rats

摘要:

目的 在脑的正常发育及一些病理条件下 ,一氧化氮合酶 (NOS)发挥一定作用 ,但不同亚型的NOS作用不同。该研究观察正常新生鼠脑以及内毒素血症时新生鼠脑 3种一氧化氮合酶 (NOS)亚型蛋白的表达 ,并探讨脂多糖 (LPS)和地塞米松 (DXM)对其表达的影响。方法 生后健康 7日龄Wistar大鼠 6 8只 ,随机分为对照组、内毒素血症组 (腹腔内注射E .coliLPS 5mg kg)及DXM组 (LPS 5mg kg +DXM 10mg kg) ,分别于用药后2 ,4 ,6 ,2 4h取脑进行NOS免疫组织化学染色。结果 正常对照组新生大鼠脑神经元型NOS(nNOS)明显表达 ,内皮型NOS(eNOS)微弱表达 ,诱导型NOS(iNOS)无表达。LPS腹腔注射后 4hnNOS表达开始增加 ;eNOS及iNOS表达于 6h开始增加 ,3者表达均于 2 4h时达高峰 ;3种NOS表达阳性细胞主要分布于脑皮质、海马、下丘脑、脑室旁核团、纹状体神经细胞。除此之外 ,nNOS在梨状皮质有较强表达 ,eNOS及iNOS在血管内皮细胞呈微弱表达。3种NOS亚型蛋白表达在DXM注射后 2～ 6h受到明显抑制 ,并持续至用药后 2 4h。结论 正常新生鼠脑表达nNOS及eNOS ,无iNOS表达 ;LPS诱导 3种NOS亚型的表达 ,其表达的部位及受诱导表达的程度亦不同 ,提示NOS在中枢神经系统的正常发育及LPS诱导的内毒素血症脑损伤发病中发挥一定作用 ,DXM具有神

Abstract:

Objective In the brain, three isoforms of nitric oxide synthase (NOS), namely neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS), have been implicated in biological roles, each isoform exhibiting different roles. This study aims to investigate the effects of lipopolysaccharide (LPS) and dexamethasone on the three isoforms expressions in neonatal rats by using a model of endotoxemia induced by LPS. Methods LPS (5 mg/kg) or LPS (5 mg/kg) plus dexamethasone (10 mg/kg) or sterile saline (controls) was injected intraperitoneally into 68 7-day-old Wistar rats. The rats were sacrificed 2, 4, 6 or 24 hrs after injection respectively. The expressions of NOS isoforms were examined by the immunohistochemical technique. Results nNOS was detected, but in contrast iNOS was not detectable, and eNOS was only faintly expressed in the brain of the controls. The nNOS expression was increased 4 hrs after LPS injection and the iNOS and eNOS expressions were increased 6 hrs after LPS injection. The expressions of the three isoforms reached a peak 24 hrs after LPS injection. Positive immunoreactivity was detected in the cerebral cortex, hippocampus, hypothalamus, paraventricular nucleus and striatum. In addition, nNOS was also detected in the limbic cortex. eNOS or iNOS was faintly expressed in the endothelial cells of cerebral blood vessels. The expressions of three NOS isoforms were remarkably inhibited between 2 and 6 hrs after dexamethasone administration and the inhibition effect continued until 24 hrs after administration. Conclusions nNOS and eNOS may be identified and iNOS is not detectable in the brain of normal neonatal rats. LPS can induce the expressions of three NOS isoforms, and the distribution and intensity of the expressions of three NOS isoforms varies, suggesting that NOS may play roles in the central nervous system development and brain damage in LPS-induced endotoxemia. Dexamethasone has a neuroprotective effect against brain damage induced by endotoxemia.