褪黑激素对严重烧伤早期肾功能损害的保护作用

目的观察褪黑激素（MLT）对严重烧伤大鼠肾组织氧化应激损伤和肾功能不全的保护作用及机制。方法将70只SD大鼠随机分为假手术组（10只）、烫伤组（用背部浸入沸水中30S造成30％总体表面积Ⅲ度烫伤模型，30只）和MLT治疗组（伤后立即腹腔注射MLT 10mg／kg，每12h补充注射1次，30只）。检测各组伤后6、24和72h肾组织丙二醛（MDA）和还原型谷胱甘肽（GSH）含量、血浆肌酐（BCr）及尿素氮（BUN）水平，以及伤后6h肾组织谷胱甘肽过氧化物酶（GSH-Px）和髓过氧化物酶（MPO）活性。结果烫伤后各时间点肾组织MDA水平明显升高，而GSH含量则显著下降，二者变化均以伤后6h最明显（P均〈0．01）。BCr及BUN水平在烧伤后6h达高峰（P均〈0．01），然后呈进行性下降。单次MLT治疗使伤后6h肾组织MDA水平降低27．8％（P〈0．01），使GSH含量提高44．4％（P〈0．05），并抑制BCr及BUN水平（P〈0．05和P〈0．01）。连续注射MLT对以上各指标均无明显影响。此外，MLT使烧伤后6h肾组织MPO水平降低30．2％（P〈0．05），但对GSH-Px活性无明显影响。结论30％Ⅲ度烫伤可导致大鼠肾脏发生明显的氧化应激损伤（伤后72h内）及急性肾功能不全（伤后24h内），单次MLT治疗对二者均具有一定的保护作用，可能与MLT具有强大的自由基清除能力及抑制中性粒细胞聚集有关。

Protective effect of melatonin against renal dysfunction following severe burn in rats

OBJECTIVE: To explore the protective effect of melatonin (MLT) against renal dysfunction in the early stage of burn in rats. METHODS: Seventy SD rats were randomly assigned to three groups: sham control (n=10), burn control (n=30) and MLT group (n=30). The 30% total body surface area (TBSA) full-thickness burn was induced by immersing the dorsal skin into boiling water for 30 seconds, while MLT (10 mg/kg, i.p.) was given immediately postburn, and the same dose was repeated once after 12 hours. The contents of malondialdehyde (MDA) and reduced glutathione (GSH) in renal tissue, as well as plasma creatinine (BCr) and urea nitrogen (BUN) levels were measured at 6, 24 and 72 hours postburn, while the activities of glutathione peroxidase (GSH-Px) and myeloperoxidase (MPO) of renal tissue were measured only at 6 hours postburn. RESULTS: MDA content was significantly increased and GSH content was decreased in renal tissue after a 30 % TBSA full-thickness burn at all time points. Plasma BCr and BUN levels were elevated within 24 hours postburn. All these changes peaked at 6 hours postburn (all P<0.01). Single injection of MLT decreased MDA by 27.8% (P<0.01) but increased GSH by 44.4% (P<0.05). It also inhibited the rise in plasma BCr and BUN levels (P<0.05 and P<0.01). However, repeated MLT injection did not show additional effect on these parameters as single injection of MLT. In addition, single dose of MLT also lowered the MPO level by 30.2% (P<0.05), but did not improve the GSH-Px activity at 6 hours postburn. CONCLUSION: Severe burn may result in obvious oxidative stress (within 72 hours postburn) in the kidney with acute renal dysfunction (within 24 hours postburn). Single injection of MLT partially counteracted these changes, due to its high free radical scavenging capacity as well as its inhibitory effect on neutrophil-mediated tissue injury.