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目的观察严重烧伤大鼠胸腺诱导型一氧化氮合酶(iNOS)表达对胸腺细胞凋亡的影响,探讨一氧化氮(NO)与胸腺病理损害的关系。方法将56只雄性Wistar大鼠随机分为对照组(8只)、烧伤组(24只)、烧伤+硫酸甲基异硫脲(SMT)组(24只)。后两组大鼠背部造成30％TBSAⅢ度烧伤,伤后分别立即静脉注射等渗盐水、等渗盐水+SMT(7．5 mg／kg);对照组不予烧伤及SMT处理。两烧伤组分别于伤后6、24、72 h检测胸腺重量、胸腺细胞凋亡情况(原位缺口末端标记法)、胸腺iNOS表达情况(免疫组织化学染色法),采用体视学方法测定阳性细胞密度,每时相点8只;同时测定对照组相应指标。结果烧伤组大鼠伤后24、72 h胸腺重量分别为(153±14)、(91±22)mg,明显轻于对照组[(243±12)mg,P<0．01];烧伤+SMT组此时明显高于烧伤组(P<0．01)。对照组大鼠胸腺皮、髓质可见散在少量凋亡阳性细胞、iNOS阳性细胞。烧伤组大鼠伤后6 h胸腺皮质有凋亡阳性细胞及少量iNOS阳性细胞;伤后24 h时凋亡阳性细胞分布于被膜下皮质、皮髓交界处及髓质,iNOS阳性细胞广泛出现在小叶间隔内血管旁;伤后72 h时凋亡阳性细胞使胸腺皮质广泛呈现棕褐色;伤后6～72 h烧伤组iNOS阳性细胞呈进行性增加(P<0．05)。烧伤+SMT组大鼠伤后各时相点阳性细胞较少且分布不均,凋亡灶少见,未见iNOS阳性细胞。烧伤组大鼠伤后24、72 h凋亡阳性细胞密度分别为(2．428±0．728)×10-5／μm3、(5．586±1．233)×10-5／μm3,高于对照组和烧伤+ SMT组(P<0．01)。结论严重烧伤大鼠伤后早期胸腺细胞凋亡率增加,iNOS在胸腺表达增强并促进了胸腺细胞凋亡;SMT则能部分改善这一现象。
Objective To observe the effect of iNOS expression on thymocyte apoptosis in severely burned rats and to explore the relationship between nitric oxide (NO) and thymus lesions. Methods Fifty - six male Wistar rats were randomly divided into control group (n = 8), burn group (n = 24) and burn group + SMT group (24). The back of the rats in the latter two groups had a 30% TBSA degree burn on the back. Immediately after the injury, they were treated with isotonic saline and isotonic saline + SMT (7.5 mg / kg) respectively. The control group was given no burn and SMT treatment. Thymus weight, thymus cell apoptosis (in situ nick end labeling) and thymus iNOS expression (immunohistochemical staining) were detected at 6, 24 and 72 h after injury in both burn groups, and the positive rate was determined by stereological method Cell density, each phase point 8; the same time, the control group measured the corresponding indicators. Results The weight of thymus in burn group was (153 ± 14) and (91 ± 22) mg at 24h and 72h, respectively, which was significantly lower than that in control group [(243 ± 12) mg, P <0.01] SMT group was significantly higher than the burn group (P <0.01). In the control group, a small amount of apoptotic positive cells and iNOS positive cells scattered in thymus and medulla were observed. At 6 hours after injury, apoptotic positive cells and a few iNOS positive cells were found in the thymus cortex at 6 hours after injury in rats. At 24 hours after injury, apoptotic positive cells were found in the subencapsular cortex, the junction of the dermis and medulla, and iNOS positive cells appeared widely The apoptotic positive cells at 72 h after injury showed thymus cortex extensively brown; iNOS positive cells in burn group increased progressively (P <0.05) 6 to 72 h after injury. Burn + SMT group rats at each time point after injury less positive and uneven distribution of apoptotic lesions rare, no iNOS positive cells. The density of apoptotic cells in burn group at 24 and 72 h were (2.428 ± 0.728) × 10-5 / μm3 and (5.586 ± 1.233) × 10-5 / μm3, respectively In the control group and burn + SMT group (P <0.01). Conclusion The apoptotic rate of thymocytes in the severely burned rats increased at the early stage, the expression of iNOS increased in the thymus and the apoptosis of thymocytes was promoted. SMT could partially improve this phenomenon.