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Haller VL, Stevens DL, Welch SP: Modulation of opioids via protection of anandamide degradation by fatty acid amide hydrolase. Eur J Pharmacol. 2008 Dec 14;600(1-3):50-8. Epub 2008 Aug 20.
Lack of involvement of the opioid system with the endocannabinoid, arachidonylethanolamide (anandamide) was possibly due to hydrolysis by fatty acid amide hydrolase (FAAH). Cyclohexylcarbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB597) is an inhibitor of FAAH, increases brain anandamide levels and enhances anandamide-induced antinociception in male ICR mice (25-30 g). The combination of URB597 (10 mg/kg, i.p.) and anandamide (40 mg/kg, i.p.) produced maximal antinociception in the mouse tail-flick test [68.7+/-16.8 percent maximum possible effect (%MPE)], versus either substance alone (27.3+/-7.9%MPE and 4.6+/-2.3%MPE, respectively) and is significantly blocked (p <0.05) by the cannabinoid CB (1) receptor antagonist, SR141716A (rimonabant), the kappa opioid receptor-selective antagonist, nor-Binaltorphimine (10 microg i.t.; 12.7+/-4.0%MPE) and the mu opioid receptor antagonist, naloxone (1 mg/kg, s.c.; 6.0+/-3.8%MPE), but not by the delta opioid receptor-selective antagonist, naltrindole (2 mg/kg, s.c.; 29.7+/-8.2%MPE) or the cannabinoid CB (2) receptor antagonist, SR144528. In addition, nor-BNI (10 microg i.t) administration to FAAH (-/-) knockout mice produced a nociceptive response. The URB597/anandamide combination was not active in the CB (1)(-/-) knockout mice, but retained activity in the MOR (-/-) knockout mice. The sub-active combination of (URB597 10 mg/kg, i.p/anandamide 10 mg/kg, i.p.; 15.5+/-4.3%MPE) shifted the dose response curve of morphine to the left (morphine alone ED (50)=4.6 mg/kg [3.7-5.6] versus morphine/URB597/anandamide (ED (50)=2.5 mg/kg [1.9-3.4]). These data are the first demonstration that anandamide, if protected from degradation, acts via the CB (1) receptor to interact with kappa opioid receptor systems in opioid analgesia. |
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