European journal of pharmacology
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The analgesic effect of indomethacin was investigated by using the visceral pain model in rabbits. After intravenous administration of indomethacin (2 mg/kg), the maximum increase of the visceral pain threshold was 0.42 +/- 0.31 mA (P < 0.05). The analgesic effect lasted 40 min. ⋯ The results imply that prostaglandins of the central nervous system could induce hyperalgesia. Indomethacin injected centrally and peripherally has an analgesic effect on visceral pain. This analgesic effect is mediated by alpha-adrenoceptors. beta-Endorphin does not participate in the analgesic action of indomethacin.
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(+)-cis-Dioxolane (0.5-2 micrograms), a muscarinic receptor agonist, given intracerebroventricularly (i.c.v.) produced a dose-dependent inhibition of the tail-flick response in male ICR mice. (+)-cis-Dioxolane given i.c.v. at a subanalgesic dose (0.25 micrograms), selectively potentiated the antinociceptive response induced by i.c.v. administered beta-endorphin, an epsilon-opioid receptor agonist, but not morphine or [D-Ala2,NMePhe4,Gly5-ol]enkephalin (DAMGO), mu-opioid receptor agonists, [D-Pen2,D-Pen5]enkephalin (DPDPE), a delta receptor agonist, or trans(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]- benzeneacetamide methane sulfonate (U50,488H), a kappa-opioid receptor agonist. The antinociceptive response induced by (+)-cis-dioxolane given i.c.v. was attenuated by i.c.v. treatment with N omega-nitro-L-arginine (1 microgram), hemoglobin (120 micrograms) or methylene blue (10 micrograms). The antinociception induced by carbachol given i.c.v. was also antagonized by the i.c.v. treatment with N omega-nitro-L-arginine (1 microgram). ⋯ The potentiation of beta-endorphin-induced antinociception by (+)-cis-dioxolane was reversed by i.c.v. treatment with N omega-nitro-L-arginine (1 microgram), hemoglobin (120 micrograms) or methylene blue (10 micrograms). On the other hand, the antinociceptive response induced by (+)-cis-dioxolane (1 microgram) given i.c.v. was potentiated by i.c.v. administered L-arginine (20 micrograms) but not D-arginine (20 micrograms). Dibutyryl cyclic GMP at 0.5-2.0 micrograms given i.c.v. produced an antinociceptive response and at subanalgesic dose (0.1 microgram) potentiated i.c.v. beta-endorphin-induced antinociception.(ABSTRACT TRUNCATED AT 250 WORDS)