Heinzen Erin L, Booth Raymond G, Pollack Gary M
Division of Drug Delivery and Disposition, School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599-7360, USA.
Biochem Pharmacol. 2005 Feb 15;69(4):679-88. doi: 10.1016/j.bcp.2004.11.004. Epub 2005 Jan 7.
NO is a key mediator of morphine antinociceptive tolerance. This work was conducted to evaluate the specific effects of NO on mu-opioid receptor activity. To investigate the effects of morphine- and L-arginine (the NO precursor)-induced increases in NO, five groups of rats were treated with saline, l-arginine (100-, 300-, or 500-mg/kg/h), or morphine 3-mg/kg/h for 8h on Day 1; brain tissue was collected on Day 2. To evaluate the effects of additional increases in NO on morphine-induced alterations of the mu-opioid receptor, six groups of rats were treated with 8-h intravenous infusions for two consecutive days as per the following scheme (Day 1:Day 2): saline:saline (control); saline:morphine 3-mg/kg/h (tolerant); L-arginine 500-mg/kg/h:saline (NO control); L-arginine 100-mg/kg/h:morphine 3-mg/kg/h; L-arginine 300-mg/kg/h:morphine 3-mg/kg/h; and L-arginine 500-mg/kg/h:morphine 3-mg/kg/h (supertolerant). Brain tissue was collected at the end of Day 2. The time course of effects on morphine-induced receptor alterations due to increased NO also was evaluated. Brain tissue was analyzed for changes in radioligand (agonist and antagonist) binding and [(35)S]GTPgammaS binding (agonist and antagonist). In the absence of agonist exposure, NO produced an alteration in the mu-opioid receptor that increased receptor activity. In the presence of agonist, NO increased constitutive activation of the mu-opioid receptor and reduced the ability of a selective mu-opioid agonist to activate the mu-opioid G-protein-coupled receptor; these molecular effects occurred in a time course consistent with the development of antinociceptive tolerance. This work establishes important NO-induced alterations in mu-opioid receptor functionality, which directly lead to the development of opioid antinociceptive tolerance.
一氧化氮（NO）是吗啡抗伤害感受性耐受的关键介质。本研究旨在评估NO对μ-阿片受体活性的具体影响。为了研究吗啡和L-精氨酸（NO前体）诱导的NO增加的影响，将五组大鼠在第1天用生理盐水、L-精氨酸（100、300或500mg/kg/h）或吗啡3mg/kg/h处理8小时；在第2天收集脑组织。为了评估NO进一步增加对吗啡诱导的μ-阿片受体改变的影响，将六组大鼠按照以下方案连续两天进行8小时静脉输注（第1天：第2天）：生理盐水：生理盐水（对照）；生理盐水：吗啡3mg/kg/h（耐受）；L-精氨酸500mg/kg/h：生理盐水（NO对照）；L-精氨酸100mg/kg/h：吗啡3mg/kg/h；L-精氨酸300mg/kg/h：吗啡3mg/kg/h；以及L-精氨酸500mg/kg/h：吗啡3mg/kg/h（超耐受）。在第2天结束时收集脑组织。还评估了由于NO增加对吗啡诱导的受体改变的作用时间进程。分析脑组织中放射性配体（激动剂和拮抗剂）结合以及[(35)S]GTPγS结合（激动剂和拮抗剂）的变化。在没有激动剂暴露的情况下，NO引起μ-阿片受体的改变，增加了受体活性。在有激动剂存在的情况下，NO增加了μ-阿片受体的组成性激活，并降低了选择性μ-阿片激动剂激活μ-阿片G蛋白偶联受体的能力；这些分子效应的发生时间进程与抗伤害感受性耐受的发展一致。本研究确定了NO诱导的μ-阿片受体功能的重要改变，这直接导致了阿片类抗伤害感受性耐受的发展。
