Spinal antinociceptive action of loperamide is mediated by opioid receptors in the formalin test in rats.
Opioids like morphine produce antinociception after intrathecal administration. Being hydrophilic in nature, morphine also spreads rostrally which leads to respiratory depression. Loperamide has been reported to produce antinociception after both intracisternal and intrathecal administration. It is also hydrophobic, which could restrict its diffusion in the spinal canal. However, the mechanism of its antinociceptive action after intrathecal administration is not definitely known. In the present study, the antinociceptive effect of loperamide was evaluated by the formalin test. It significantly inhibited Phase II flinching behavior. This antinociceptive effect was reversed by pre-administration of naloxone indicating that it was predominantly due to activation of opioid receptors.
Ray
Subrata Basu
SB
Department of Anesthesiology, University Of California - San Diego, La Jolla, CA 92093-0818, USA. sbr_aiims@hotmail.com
Yaksh
Tony L
TL
D000700:Analgesics; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D005557:Formaldehyde; D007278:Injections, Spinal; D008139:Loperamide / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*
D000700:Analgesics; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D005557:Formaldehyde; D009270:Naloxone; D008139:Loperamide