胍丁胺对神经病理性痛大鼠吗啡镇痛作用及耐受的影响

Effect of agmatine on morphine analgesia and tolerance in a rat model of neuropathic pain

目的探讨胍丁胺对神经病理性痛大鼠吗啡镇痛作用及耐受的影响。方法雄性SD 大鼠,体重160-180 g,制备坐骨神经慢性束缚性损伤(CCI)模型,用von Frey丝测定各项实验中给药前及给药后30、60、120、180、240min时机械缩腿阈值(PWT),并根据PWT计算药物最大可能镇痛百分率(PMAP)。1.选取CCI模型大鼠35只,随机分为5组(n=7),分别腹腔注射等体积生理盐水及40、60、80、100mg/kg胍丁胺,测定PWT并确定给药后30min PMAP<40%时胍丁胺的剂量;选取CCI模型大鼠35只,随机分为5组(n=7),分别皮下注射等体积生理盐水及1、2、3、5 mg/kg吗啡,测定PWT并确定给药后30min PMAP<40%时吗啡的剂量;2.选取CCI模型大鼠56只,随机分为8组(n=7),观察胍丁胺与吗啡的相互作用,计算PMAP;3.选取CCI模型大鼠35只,随机分为5组(n=7),诱导吗啡耐受产生,观察不同剂量胍丁胺与吗啡联合应用时PMAP的变化。结果大鼠腹腔注射胍丁胺后30 min PMAP高于注射生理盐水大鼠(P<0.01)。大鼠皮下注射吗啡后30min PMAP高于注射生理盐水大鼠(P<0.01)。与单独给予吗啡和单独给予胍丁胺比较,胍丁胺60mg/kg可使吗啡PMAP升高(P< 0.01),镇痛时间延长(P<0.05)。吗啡耐受实验第6天腹腔注射胍丁胺+皮下注射吗啡大鼠PMAP 高于注射生理盐水吗啡大鼠(P<0.01)。结论胍丁胺对神经病理性痛大鼠具有镇痛作用,且能增强吗啡的镇痛作用,抑制吗啡耐受的形成。

Objective To evaluate the effects of different doses of agmatine on morphine analgesia and tolerance in a rat model of neuropathic pain induced by chronic constrictive injury （CCI） of sciatic nerve.Methods Adult male SD rats weighing 160-180 g were used in this study. The animals were anesthetized with intraperitoneal （ i. p. ） pentobarbital 40 mg· kg^- 1. The right sciatic nerve was exposed and 4 loose ligatures were placed at 1-2 mm interspace. Two weeks after CCI, paw-withdrawal threshold （PWT） to yon Frey monofilaments producing different pressure was measured. Neuropathic pain model was considered established when PWT reached 2-6 g and the animal could be used in the experiment. The experiment consisted of 3 parts. Part Ⅰ （the analgesic effect of agmatine and morphine） possible maximum analgesia percentage （PMAP） of morphine and agmatine was measured. Different doses of morphine （0, 1, 2, 3, 5 mg·kg^-1） and agrnatine （0, 40, 60, 80,100 mg·kg^-1） were given. PWT was measured before and 30, 60, 120, 180 and 240 min after drug administration. PMAP was calculated. PMAP（%） = （PWT value after drug- PWT value before drug） / （26 - PWT value before drug） × 100% （26 g is the ceiling value of PWT）. PMAP〉 25% signified analgesic effect. Part Ⅱ （the effect of agrnatine on analgesic effect of morphine）. Fifty-six animals with neuropathic pain were randomly divided into 4 groups （ n = 14 each）. Each group received NS or agmatine 20, 40 or 60 mg· kg^-1. 30 min later each group received either NS or morphine 1 mg·kg^-1 （ n = 7 each）. PWT was measured and PMAP was calculated. Part Ⅲ （the effects of agrnatine on the development of morphine tolerance）. Morphine tolerance was incuced by morphine 10 mg· kg^- 1 , 3 times a day for 5 days. Thirty-five animals with neuropathic pain were randomly divided into 5 groups （ n = 7 each）： group A received NS： group B received NS ＋ morphine; grouop C, D, E received agmatine 5, 10, 20 mg · kg^- 1 ＋ morphine 3 times a day for 5 days. PWT was measured on the 5th day and PMAP was calculated. Results PMAP of agmatine （40, 60 mg·kg^-1 i.p. ） and morphine （1 mg·kg^-1 s.c. ） were lower than 40%. Agmatine 60 mg·kg^-1 increased the PMAP of morphine 1 mg·kg^-1 to 84% compared with 34% for morphine alone （P 〈 0.01）. Chronic morphine treatment for 6 days induced tolerance and the PMAP was reduced from 80% to 20%. PMAP of agmatine 20 mg· kg ＋ morphine was increased from 20% to 90% （ P 〈 0.01 ）. Conclusion Agmatine enhances morphine analgesia and inhibits morphine tolerance in a rat model of neuropathic pain.