Department of Pharmacology, Institute of Biological Sciences, ICB-UFMG, Av. Antonio Carlos, 6627, Pampulha, CEP 31.270-100, Belo Horizonte, Minas Gerais, Brazil.
Anesth Analg. 2013 Feb;116(2):463-72. doi: 10.1213/ANE.0b013e3182707859. Epub 2013 Jan 9.
Cannabinoid agonists induce norepinephrine release in central, spinal, and peripheral sites. Previous studies suggest an interaction between the cannabinoid and adrenergic systems on antinociception. In this study, we sought to verify whether the CB1 and CB2 cannabinoid receptor agonists anandamide and N-palmitoyl-ethanolamine (PEA), respectively, are able to induce peripheral antinociception via an adrenergic mechanism.
All drugs were administered locally into the right hindpaw of male Wistar rats. The rat paw pressure test was used, with hyperalgesia induced by intraplantar injection of prostaglandin E2 (2 μg).
Anandamide, 12.5 ng/paw, 25 ng/paw, and 50 ng/paw elicited a local peripheral antinociceptive effect that was antagonized by CB1 cannabinoid receptor antagonist AM251, 20 µg/paw, 40 µg/paw, and 80 µg/paw, but not by CB2 cannabinoid receptor antagonist AM630, 100 µg/paw. PEA, 5 µg/paw, 10 µg/paw, and 20 µg/paw, elicited a local peripheral antinociceptive effect that was antagonized by AM630, 25 µg/paw, 50 µg/paw, and 100 µg/paw, but not by AM251, 80 µg/paw. Antinociception induced by anandamide or PEA was antagonized by the nonselective α2 adrenoceptor antagonist yohimbine, 05 µg/paw, 10 µg/paw, and 20 µg/paw, and by the selective α2C adrenoceptor antagonist rauwolscine, 10 µg/paw, 15 µg/paw, and 20 µg/paw, but not by the selective antagonists for α2A, α2B, and α2D adrenoceptor subtypes, 20 μg/paw. The antinociceptive effect of the cannabinoids was also antagonized by the nonselective α1 adrenoceptor antagonist prazosin, 0.5 µg/paw, 1 µg/paw, and 2 µg/paw, and by the nonselective β adrenoceptor antagonist propranolol, 150 ng/paw, 300 ng/paw, and 600 ng/paw. Guanethidine, which depletes peripheral sympathomimetic amines (30 mg/kg/animal, once a day for 3 days), restored approximately 70% the anandamide-induced and PEA-induced peripheral antinociception. Furthermore, acute injection of the norepinephrine reuptake inhibitor reboxetine, 30 µg/paw, intensified the antinociceptive effects of low-dose anandamide, 12.5 ng/paw, and PEA, 5 µg/paw.
This study provides evidence that anandamide and PEA induce peripheral antinociception activating CB1 and CB2 cannabinoid receptors, respectively, stimulating an endogenous norepinephrine release that activates peripheral adrenoceptors inducing antinociception.
大麻素激动剂在中枢、脊髓和外周部位诱导去甲肾上腺素释放。先前的研究表明大麻素和儿茶酚胺系统在镇痛作用上存在相互作用。在这项研究中，我们试图验证 CB1 和 CB2 大麻素受体激动剂分别为大麻素和 N-棕榈酰-乙醇胺（PEA）是否能够通过肾上腺素能机制诱导外周镇痛。
所有药物均局部注射入雄性 Wistar 大鼠的右后爪。使用足底注射前列腺素 E2（2μg）诱导的痛觉过敏来进行大鼠爪压力测试。
12.5ng/爪、25ng/爪和 50ng/爪的大麻因引起局部外周镇痛作用，该作用被 CB1 大麻素受体拮抗剂 AM251（20μg/爪、40μg/爪和 80μg/爪）拮抗，但不能被 CB2 大麻素受体拮抗剂 AM630（100μg/爪）拮抗。5μg/爪、10μg/爪和 20μg/爪的 PEA 引起局部外周镇痛作用，该作用被 AM630（25μg/爪、50μg/爪和 100μg/爪）拮抗，但不能被 AM251（80μg/爪）拮抗。大麻因或 PEA 诱导的镇痛作用被非选择性α2 肾上腺素能受体拮抗剂育亨宾（0.5μg/爪、1μg/爪和 2μg/爪）和选择性α2C 肾上腺素能受体拮抗剂雷唑林（10μg/爪、15μg/爪和 20μg/爪）拮抗，但不能被α2A、α2B 和α2D 肾上腺素能受体亚型的选择性拮抗剂（20μg/爪）拮抗。大麻素的镇痛作用也被非选择性α1 肾上腺素能受体拮抗剂哌唑嗪（0.5μg/爪、1μg/爪和 2μg/爪）和非选择性β 肾上腺素能受体拮抗剂普萘洛尔（150ng/爪、300ng/爪和 600ng/爪）拮抗。胍乙啶（每天一次，30mg/kg/动物，共 3 天）可消耗外周拟交感神经胺，使大麻因和 PEA 诱导的外周镇痛作用分别恢复约 70%。此外，急性注射去甲肾上腺素再摄取抑制剂瑞波西汀（30μg/爪）增强了低剂量大麻因（12.5ng/爪）和 PEA（5μg/爪）的镇痛作用。
本研究提供的证据表明，大麻因和 PEA 分别通过激活 CB1 和 CB2 大麻素受体诱导外周镇痛，刺激内源性去甲肾上腺素释放，激活外周肾上腺素能受体诱导镇痛。
