Continuous intrathecal opioid treatment abolishes the regulatory effects of magnesium and guanine nucleotides on mu opioid receptor binding in rat spinal membranes.
Continuous intrathecal opioid treatment abolishes the regulatory effects of magnesium and guanine nucleotides on mu opioid receptor binding in rat spinal membranes.
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发表时间：
1992-07
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通讯作者：
C. Wong;Y. F. Su;W. Watkins;K. Chang
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作者：
C. Wong;Y. F. Su;W. Watkins;K. Chang
在大鼠脊髓模型中研究了阿片类药物和百日咳毒素处理后阳离子和鸟嘌呤核苷酸对mu受体结合的调节作用。连续鞘内输注PL017 5天，以剂量依赖性方式诱导耐受性。在第2天观察到最大耐受性。单剂量（1微克）百日咳毒素也诱导对阿片类药物的耐受性。当用125I-FK33824测定高亲和力位点的mu受体结合时，吗啡和百日咳毒素诱导的耐受动物的脊髓膜制剂的结合比对照膜少约30%。FK33824在多种实验条件下（即阳离子和鸟嘌呤核苷酸）对[3H]纳洛酮的平衡竞争结合分析揭示了对照膜和处理膜之间的差异。在Na+ (100 mM) + GDP（100微米）预处理膜和Mg++存在下进行的结合实验中，观察到所有mu受体在对照膜中处于高亲和力状态，而在阿片类药物和百日破毒素处理动物的膜中约有30%的受体处于低亲和力状态。低亲和力位点比例的增加依赖于PL017的输注剂量，且与阿片耐受性的发展程度密切相关。在百日咳毒素或阿片类药物处理的动物的膜中，5'-鸟酰脲二磷酸对阿片激动剂结合的调节作用降低。在Na+ (100 mM) + Mg++ (5 mM) + 5'-胍脲二磷酸（30微米）或Na+ (100 mM) + GDP（100微米）存在下进行的结合试验中，对照膜上的所有mu受体都处于低亲和力状态，而来自阿片类药物或百日破毒素处理的动物的mu受体则存在高亲和力和低亲和力状态。以1微克/小时的高剂量连续滴注PL017 5天，受体总数也显著减少（约40%）。这些研究表明，持续的阿片输注和百日咳毒素治疗导致受体- g蛋白偶联损伤。这反映在Mg++和鸟嘌呤核苷酸的调节作用减弱。因此，除了高剂量PL017诱导受体下调外，受体- g蛋白解偶联可能在持续输注吗啡和PL017诱导的阿片样物质耐受中发挥作用。
The regulatory effects of cations and guanine nucleotides on mu receptor binding after opioid drug and pertussis toxin treatment were studied in the rat spinal cord model. Continuous intrathecal (i.t.) infusion with PL017 for 5 days induced tolerance in a dose-dependent manner. Maximal tolerance was observed at day 2. A single i.t. dose (1 microgram) of pertussis toxin also induced tolerance to opioid. When mu receptor binding of the high-affinity sites was determined by 125I-FK33824, spinal membrane preparations from morphine- and pertussis toxin-induced tolerant animals demonstrated approximately 30% less binding than control membranes. Analysis of equilibrium competition binding of FK33824 against [3H]naloxone under a variety of experimental conditions (i.e., cations and guanine nucleotides) revealed differences among control and treated membranes. With Na+ (100 mM) + GDP (100 microM) pretreated membranes and binding assays conducted in the presence of Mg++, all mu receptors were observed to be in a high-affinity state in control membranes, whereas about 30% of receptors were in the low-affinity state in membranes from opioid- and pertussis toxin-treated animals. The increase in the proportion of low-affinity sites was dependent upon the infusion dose of PL017, and the increase correlated well with the degree of opioid tolerance developed. The regulatory effect of 5'-guanylylimidodiphosphate on opioid agonist binding was reduced in membranes from pertussis toxin- or opioid-treated animals. In binding assays conducted in the presence of Na+ (100 mM) + Mg++ (5 mM) + 5'-guanylylimidodiphosphate (30 microM) or Na+ (100 mM) + GDP (100 microM), all mu receptors in control membranes were in a low affinity-state, while those from opioid- or pertussis toxin-treated animals existed in both the high- and the low-affinity states. Continuous i.t. infusion with PL017 at the high dose of 1 microgram/hr for 5 days also decreased significantly (about 40%) the total number of receptors. These studies indicate that continuous opioid infusion and pertussis toxin treatment results in impairment in the receptor-G-protein coupling. This is reflected by the decreased regulatory effects of Mg++ and guanine nucleotides. Thus, in addition to receptor down-regulation, which is induced by PL017 at high doses, receptor-G-protein uncoupling may play a role in opioid tolerance induced by continuous infusion with morphine and PL017.