European journal of pharmacology
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The effects of the kappa-opioid receptor agonist, TRK-820, (-)-17-(cyclopropylmethyl)-3, 14beta-dihydroxy-4, 5alpha-epoxy-6beta-[N-methyl-trans-3-(3-furyl) acrylamido] morphinan hydrochloride, on the itch sensation were compared with those of histamine H1 receptor antagonists, using the mouse pruritogen-induced scratching model. Peroral administration of TRK-820 reduced the numbers of substance P- or histamine-induced scratches dose dependently. No obvious suppression of the spontaneous locomotor activity was observed at the doses used for the experiments, indicating that the inhibition of scratches was not due to the effect on general behavior. ⋯ Histamine H1 receptor antagonists, chlorpheniramine and ketotifen, did not inhibit substance P-induced scratches, or did so only partially. Both antihistamines inhibited the histamine-induced scratches completely. These results suggest that TRK-820 has antipruritic activity which is mediated by kappa-opioid receptors, and is effective in both antihistamine-sensitive and -resistant pruritus.