Analgesic action of loperamide, an opioid agonist, and its blocking action on voltage-dependent Ca2+ channels

Kunie Hagiwara, Osamu Nakagawasai, Atsunobu Murata, Fumihiro Yamadera, Ichiro Miyoshi, Koichi Tan-No, Takeshi Tadano, Teruyuki Yanagisawa, Toshihiko Iijima, Manabu Murakami

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)


We investigated the relationship between the antinociceptive effect of the opiate agonist loperamide at the spinal level and its inhibitory effect on calcium influx. Intrathecal administration of loperamide showed a significant antinociceptive effect in the formalin test, which was not prevented by naloxone. On the other hand, no significant effects were observed by nicardipine, an L-type specific blocker, or by BAY K8644, an L-type specific agonist, suggesting no significant role of L-type calcium channels in nociceptive signal transduction. Loperamide suppressed the calcium influx in dorsal root ganglion neurons. As the antinociceptive effect of loperamide was not affected by naloxone or other calcium channel blocking toxins, and loperamide showed a direct inhibitory effect on calcium-influx, the analgesic effect of intrathecally injected loperamide might be due to its blockade of the voltage-dependent calcium channels at the terminals of the primary afferent fibers.

Original languageEnglish
Pages (from-to)493-497
Number of pages5
JournalNeuroscience Research
Issue number4
Publication statusPublished - 2003 Aug 1


  • Analgesia
  • Calcium channels
  • DRG neuron
  • Formalin
  • Loperamide
  • Mice

ASJC Scopus subject areas

  • Neuroscience(all)


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