title: Effects of chlorpheniramine and ranitidine on the visceral nociception induced by acetic acid in rats: role of opioid system.
abstract: In this study, effects of chlorpheniramine (H1-receptor blocker), ranitidine (H2-receptor blocker), morphine (an opioid agonist) and naloxone (an opioid antagonist) in separate and combined treatments were investigated on the visceral nociception in rats. Visceral nociception was induced by intraperitoneal injection of acetic acid (1 mL, 1%). The latency time to the beginning of the first abdominal wall contraction (first writhe) was measured and the numbers of writhes were counted for 1 h after acetic acid injection. Intraperitoneal injections of chlorpheniramine and ranitidine significantly (p < 0.05) increased the latency time to the beginning of the first writhe and also significantly (p < 0.05) decreased the numbers of writhes. The same results were obtained after subcutaneous injection of morphine. Subcutaneous injection of naloxone did not change the intensity of visceral nociception, but significantly (p < 0.05) prevented the morphine-induced antinociception. Intraperitoneal injection of chlorpheniramine significantly (p < 0.05) enhanced the morphine-induced analgesia, but did not reverse the effect of naloxone on nociceptive responses. Intraperitoneal injection of ranitidine, with no effect on the morphine-induced antinociception, significantly (p < 0.05) reversed the effect of naloxone on pain responses. These results suggest that both chlorpheniramine and ranitidine exert antinociceptive effect in the visceral nociception. In addition, morphine through a naloxone-dependent mechanism produces visceral antinociception. Moreover, the endogenous opioid system may participate in the chlorpheniramine- but not in the ranitidine-induced antinociception.
authors.affiliation: Section of Physiology, Department of Basic Sciences, Faculty of Veterinary Medicine, Urmia University, P.O. Box 1177, Urmia 57135, Urmia, Iran.
authors.forename: A
authors.initials: A
authors.lastname: Zanboori
authors.forename: E
authors.initials: E
authors.lastname: Tamaddonfard
authors.forename: A
authors.initials: A
authors.lastname: Mojtahedein
mesh_terms: D019342:Acetic Acid / Q000633:toxicity*; D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D002744:Chlorpheniramine / Q000494:pharmacology*; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology*; D018847:Opioid Peptides / Q000502:physiology*; D010147:Pain Measurement; D011899:Ranitidine / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000700:Analgesics; D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D009292:Narcotic Antagonists; D009294:Narcotics; D018847:Opioid Peptides; D009270:Naloxone; D002744:Chlorpheniramine; D009020:Morphine; D011899:Ranitidine; D019342:Acetic Acid