Visceral analgesic tolerance to intrathecal butorphanol in ratsPurpose: Recent experimental data suggest that intrathecal (it) K-opioid agonists produce profound visceral analgesia. This study investigated the development of visceral analgesic tolerance to it butorphanol, a potent K-agonist that has fewer side effects than commonly used it opioids. Understanding of this tolerance could make it butorphanol more effective in treating chronic visceral pain. Methods: This was a randomized, controlled animal study involving 80 Sprague-Dawley rats. Rats implanted with lumbar it catheters were infused either with it saline or butorphanol (52 nmol.hr -~) for 96 hr. Six hours afterwards, each rat was challenged once with one of the differing it butorphanol doses to construct dose-response curves. Visceral analgesia was evaluated by the abdominal writhing responses to the acetic acid injected intraperitoneally. The time of the first writhe and the total number of writhes were recorded. Results: For both the saline-and butorphanol-infused groups, a higher challenge dose of it butorphanol produced longer time for the first writhe to occur (P < 0.01, one-way ANOVA), and fewer writhes occurring within 30 min (P < 0.01, one-way ANOVA). However, the dose response curves of the butorphanol-infused groups were shifted rightward (P < 0.001, partial F test). Conclusion: The challenge doses of it butorphanol produced dose-dependent visceral analgesia in both the saline-and butorphanol-infused groups, confirming its efficacy. The butorphanol-infused groups showed doseresponse shifts, demonstrating the development of tolerance to this visceral analgesia.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.