体表镇痛剂对深部炎症痛缓解作用机制探讨

目的:本研究通过行为学和电生理学等方法 ,探索表面镇痛剂缓解机体深部组织疼痛的作用机制。方法:成年SD大鼠(雌雄各半),用完全佐剂(complete Freund’s adjuvant,CFA)构建左侧胫骨前肌炎症痛模型。随机分为2组:实验组(镇痛剂贴敷)和对照组(普通透气胶布贴敷)。分别观察大鼠的痛行为学;用伊文氏蓝的渗出测定血管渗透性;用电生理方法记录皮和肌肉的神经纤维放电情况,并观察去神经后的纤维放电情况。结果:表面镇痛剂有缓解肌肉炎症痛的作用,且具有药物特异的潜伏期(从10分钟到1~2小时)和作用时程。镇痛剂作用的皮肤区表现为血管渗出通透性增加。神经的纤维活动记录发现镇痛剂对A-纤维的兴奋性没有影响,也不能诱发其自发电活动;但却可以提高皮肤C-纤维的兴奋性,诱发C-纤维的自发电活动。电生理实验中潜伏期和作用时程与行为学实验中药物起效时间的对比证实药物对肌肉的镇痛作用与皮肤C-纤维的自发电活动相关。来自炎症肌肉的C-纤维传入电活动记录证明,表面镇痛剂可有效的抑制肌肉C-纤维的自发传入电活动;若去除药物作用的皮肤区的神经支配,则药物对深部组织的炎症痛的缓解作用消失。结论:表面镇痛剂可能通过激活皮肤的痛觉感受器,反射性减弱深部炎症肌肉的损害性传入活动。

MECHANISMS OF TOPICAL ANALGESICS IN RELIEVING PAIN IN AN ANIMAL MODEL OF MUSCULAR INFLAMMATION

Objective: To investigate the possible mechanisms of topical analgesics in relieving pain in an animal model of muscular inflammation.Methods: Adult Sprague-Dawley rats of both sex were injected with complete Freund’s adjuvant(CFA) to induce inflammation in the tibialis anterior muscle of left hindlimb,and were devided randomly into the experimental group(topical anagesics applied) and the control group(breathable plaster applied).The following experiments were performed: pain behavioral tests,evaluation of plasma extravasation in the affected limb,electrophysiologically recordings of afferent nerve fibers.Results: The behavioral experiments demonstrated that applications of topical analgesics,Xiaotongtie(XTT),a Tibet herb compound,or capsaicin(CAP),a cream containing 0.1% capsaicin,applied to the skin over the inflammed tibilalis anterior muscle significantly reduced musclar inflammatory pain,indicated by the increased body-weight loading on the affected hinglimb(with latency of 10 min for XTT and 1-2 h for CAP).Meanwhile,both analgesics caused plasma extravasation in the affected skin.Electrophysiological recordings from the afferent fibers in the related cutaneous nerve indicated that topical analgesics selectively triggered C-fibers,but not A-fibers innervating the same region of receptive field.The latency and duration of C-fiber activation was similar to those of the reduction of musclar inflammatory pain.On the contrary,topical analgesics substantially decreased C-fiber afferent spontaneous firing in the nerve innervating the inflammed muscle.Moreover,denervation of the affected skin blocked the analgesic effects of both topical analgesics in musclar inflammatory pain.Conclusion: This study suggested that topical analgesics may reduce the nociceptive input from inflamed muscles via a reflex mechanism by activating the cutaneous nociceptive afferents.