N^ω-硝基-L-精氨酸甲酯通过降低大鼠脊髓和中脑谷氨酸释放而抑制吗啡镇痛耐受形成

N^ω-NITRO-L-ARGININE METHYL ESTER INHIBITS DEVELOPMENT OF MORPHINE ANALGESIA TOLERANCE BY DECREASING GLUTAMATE RELEASE OF SPINAL CORD AND MIDBRAIN IN RATS

目的:通过福尔马林炎性刺激观察非特异性一氧化氮合成酶(NOS)抑制剂-Nω-硝基-L-精氨酸甲酯(Nω-nitro-L-arginine methylester,L-NAME)对大鼠吗啡镇痛耐受的形成以及脊髓和中脑细胞外谷氨酸含量的影响。方法:24只健康成年Sprague-Dawley大鼠随机平均分为4组(每组6只):1组,对照组,皮下注射生理盐水1ml;2组,皮下注射L-NAME20mg/kg;3组,皮下注射吗啡10mg/kg;4组,皮下注射L-NAME20mg/kg和吗啡10mg/kg。各组的皮下注射处理均为每天2次,连续7天。在第8天上午最后1次皮下注射后30min,于大鼠左后掌皮下注射5%福尔马林0.1ml,记录其每5min内舔咬注射足时间,观察时间为50min。记录完毕后断头取脊髓和中脑测定细胞外谷氨酸含量。结果:与1组相比,2组的Ⅱ相舔咬注射足时间显著缩短,3组的Ⅰ相和Ⅱ相舔咬注射足时间均显著延长,4组的Ⅰ相和Ⅱ相舔咬注射足时间均显著缩短。与1组相比,脊髓和中脑的细胞外谷氨酸含量在2组和4组显著降低,在3组显著增高(P<0.01),但是4组脊髓和中脑的细胞外谷氨酸含量较3组显著降低(P<0.05)。大鼠Ⅱ相舔咬注射足时间与脊髓和中脑细胞外谷氨酸含量呈正相关。结论:长期联合应用L-NAME和吗啡可抑制大鼠吗啡镇痛耐受的形成,该作用可能是通过抑制NOS而减少脊髓和中脑谷氨酸释放实现的。

Objectives： To observe the effects of systemic administration of nonspecific nitric oxide synthase inhibitor, N^ω-nitro-L-arginine methyl ester（L-NAME） , on development of morphine analgesia toler- ance and extracellular concentrations of glutamate in spinal cord and midbrain induced by formalin inflammatory stimulus in rats. Methods： 24 healthy adult Sprague-Dawley rats were randomly allocated equally to 4 groups （n = 6 each group） ： group 1, the control group, received a subcutaneous （s. c. ） injection of 1 ml NS; groups 2,3 and 4 received s. c. injection of L-NAME 20 mg/kg,morphine 10 mg/kg, and L-NAME 20 mg/kg and morphine 10 mg/kg,respectively. All rats received s.c. injection twice a day. Thirty minutes after last treatment in the morning of the 8th day,0.1 ml of 5% formalin was injected subcutaneously into the plantar surface of the left hindpaw. The total time spent licking injected-paw （TFSLI） within every 5 rain was recorded for 50 rain thereafter. Animals were decapitated after pain behavior observation. The spinal cord and midbrain were sampled to measure glutamate concentration by high-performance liquid chromatography （HPLC）. Results： Compared to group 1 ,TTSLI in phase Ⅱ decreased significantly in group 2,TTSLI in phases Ⅰ and Ⅱ increased significantly in group 3 and decreased significantly in group 4. The extracelluer concentrations of glutamate in spinal cord and midbrain were significantly lower in group 2 and 4 but higher in groups 3 than those in group 1, and those were significantly lower in group 4 as compared to group 3. Conclusions： Chronic codministration of L-NAME and morphine could inhibit the development of morphine analgesia tolerance in rats. This effect may contribute to decrease in glutamate release of spinal cord and midbrain by inhibiting nitric oxide synthase.