title: Analysis of the mechanisms underlying the antinociceptive effect of the extracts of plants from the genus Phyllanthus.
abstract: 1. We examine some of the mechanisms underlying the analgesic effects of the hydroalcoholic extracts (HE) of Phyllanthus urinaria and P. niruri against formalin-induced nociception in mice. In addition, we also investigate the action of both HEs against capsaicin-mediated pain. 2. Both prazosin and yohimbine (0.15 mg/kg, i.p.) induced a marked inhibition of the analgesic effect caused by phenylephrine (10 mg/kg, i.p.) and clonidine (0.1 mg/kg, i.p.), respectively, but had no effect on the antinociceptive action caused by HE of P. urinaria (10 mg/kg, i.p.) or P. niruri (30 mg/kg, i.p.). 3. NG-nitro-L-arginine (L-NOARG, 75 mg/kg, i.p.) caused marked analgesic effect against the second phase of formalin-induced pain. Treatment of animals with L-arginine (600 mg/kg) completely antagonized the antinociceptive effect of L-NOARG but had no significant effect against the HE of P. urinaria (10 mg/kg, i.p.) or P. niruri (30 mg/kg. i.p.) analgesic properties. 4. The antinociceptive effects caused by the HEs of P. urinaria (10 mg/kg, i.p.) and P. niruri (30 mg/kg, i.p.) were unaffected by methysergide (5 mg/kg, i.p.), p-chloro-phenylalanine-methyl-ester (100 mg/kg, i.p., once a day for 4 consecutive days) or after previous adrenalectomy of animals. 5. The HE of P. urinaria and P. niruri given either intraperitoneally (1-30 mg/kg) or orally (25-200 mg/kg) caused marked and dose-related inhibition of capsaicin-induced pain with ID50 of 2.1 and 6.1 mg/kg given intraperitoneally and 39 and 35 mg/kg given orally, respectively.
authors.affiliation: Department of Pharmacology, Universidade Federal de Santa Catarina, Florianópolis, Brazil.
authors.forename: A R
authors.initials: AR
authors.lastname: Santos
authors.forename: V C
authors.initials: VC
authors.lastname: Filho
authors.forename: R A
authors.initials: RA
authors.lastname: Yunes
authors.forename: J B
authors.initials: JB
authors.lastname: Calixto
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002211:Capsaicin; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008297:Male; D051379:Mice; D019335:Nitroarginine; D010146:Pain / Q000139:chemically induced / Q000517:prevention & control; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010936:Plant Extracts / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000700:Analgesics; D010936:Plant Extracts; D010656:Phenylephrine; D019335:Nitroarginine; D015016:Yohimbine; D001120:Arginine; D003000:Clonidine; D002211:Capsaicin; D011224:Prazosin