褪黑激素对严重烧伤大鼠迟发型超敏反应的影响

Effect of melatonin on delayed-type hypersensitivity in severely-burned rats

目的:观察褪黑激素对30%Ⅲ度烧伤大鼠迟发型超敏反应的影响,估计它在严重烧伤中的免疫调节作用。方法:实验于2005-07/12在青岛大学医学院完成。24只SD大鼠数字表法随机分为对照组、烧伤组及褪黑激素组,每组8只。烧伤组及褪黑激素组麻醉状态下将动物背部皮肤置于沸水中15s制备烧伤模型,对照组大鼠背部皮肤置于37℃水中15s。对照组和烧伤组伤后立即腹腔注射溶剂(体积分数为0.01的乙醇生理盐水),而褪黑激素组注射剂量为10mg/kg的褪黑激素,烧伤当天下午4点补充注射一次药物或溶剂,此后按同法每天注射一次至伤后第7天。末次注射后立即将5g/L二硝基氟苯溶液100μL涂抹于大鼠腹部,次日同法强化一次,以诱导迟发型超敏反应。致敏后第5天,测定大鼠右耳肿胀百分率(对照组定义为100%)代表迟发型超敏反应强度。此外,还测定烧伤前后外周血白细胞计数,估计动物的一般免疫反应状态。结果:24只大鼠全部进入结果分析。①右耳肿胀百分率:烧伤组大鼠显著低于对照组[(41.2±8.2)%,(100±7.6)%,P<0.001],褪黑激素组高于烧伤组[(73.0±10.1)%,P<0.01],但仍低于对照组水平(P<0.05)。②外周血白细胞计数:烧伤组及褪黑激素组大鼠在烧伤后12h内均明显升高(P<0.05),伤后72h和120h,两实验组白细胞再次出现升高(P<0.05),褪黑激素组白细胞数值在这两个时间点均明显低于烧伤组水平(P<0.05,0.01)。结论:褪黑激素治疗能明显改善烧伤大鼠严重受抑的迟发型超敏反应,提示它在烧伤中可能具有免疫调节作用。

AIM： To observe the effect of melatonin on delayed-type hypersensitivity （DTH） in severely-burned rats, and estimate the immuno-modulating effect of melatonin in burn injury. METHODS： The experiment was performed in the Medical College of Qingdao University from July to December 2005. Twenty-four SD rats were randomly assigned to three groups with 8 ones in each group： control group, burn group and melatonin group. A 30% full-thickness burn was induced under anaesthesia by immersing the dorsal skin into boiling water for exactly 15 s. The skin in the control group was immersed in water at 37 ℃ for 15 s. Immediately after burn or sham operation, both control and burn control were given intraperitoneally vehicle （1% ethanol in 0.9% saline）, while melatonin-treated animals received melatonin at a dose of 10 mg/kg. Same treatment of vehicle or melatonin was repeated at 4：00 pm daily until the 7^th day postburn. After last injection, DTH was induced by injecting 5 g/L dinitrofluorobenzene （DNFB） into rats＇ abdomen for two consecutive days. On the 5^th day of sensitization, the right car swelling percentages of rats were applied to estimate the intensity of DTH （100% in control group）. In addition, the peripheral white blood cell （WBC） was counted at preburn and postburn respectively to estimate the general immunologic reactive status of rats. RESULTS： Totally 24 rats entered the result analysis. ①Severe burn evidently depressed the DTH at postburn as reflected by the decreased ear swelling percentage [（100±7.6）%, （41.2±8.2）%, P 〈 0.001]. Melatonin therapy improved the DTH to （73.0±10.1）% （P 〈 0.01）; but did not restore it completely to the level of sham control （P 〈 0.05）.②In addition, WBC counts in both burn control and melatonin group showed an obvious rise initially within 12 hours postburn （P 〈 0.05）, and the second rise appeared at 72 and 120 hours postburn （P 〈 0.05）, However, the WBC counts in melatonin group were significantly lower than that of burn control group at the two time-points （P 〈 0.05, 0.01）. CONCLUSION： Melatonin can obviously improve the inhibited DTH in rats after severely burn, suggesting that it may act as an immunomodulating agent in burn injury.