Enhancing fentanyl antinociception and preventing tolerance with α-2 adrenoceptor agonists in rats

Fentanyl (FEN) is a potent opioid analgesic used for pain management. Opioid analgesic tolerance poses a significant challenge to the clinical utility of opioid agonists. Preventing the development of tolerance to opioid analgesia is crucial for improving its efficacy and safety. The noradrenergic system is involved in pain regulation. This study examined the effects of alpha-2 adrenoceptor (AR) agonists, dexmedetomidine (DEX), and xylazine (XYL) on FEN tolerance and antinociception, and their impact on mu-opioid receptor (MOR) expression in the posterior horn of the spinal cord (SC). Male rats were divided into six groups and treated with different drug combinations for three consecutive days. Analgesia tests and motor performance assessments were conducted, followed by SC analysis using immunohistochemistry (IHC). Analgesia tests revealed the development of FEN tolerance on the second day, but the groups receiving combined drugs did not develop tolerance. Instead, FEN antinociception was enhanced, with a prolonged duration of its effects. None of the drugs caused sedation or motor impairment, and SC morphology appeared normal. MOR expression levels did not differ significantly between the groups based on IHC analysis. These findings suggest that changes in the secondary messenger system may play a role in the early development of FEN tolerance. Combining drugs can prevent tolerance, while enhancing FEN's antinociceptive effects. These results have promising implications for chronic pain management; however, further research is needed to explore the molecular effects of alpha-2 AR agonists on FEN tolerance. Overall, this study sheds light on the mechanism of FEN tolerance and identifies potential avenues for future research.

Automated summary

This study examines the effects of alpha-2 adrenoceptor agonists on fentanyl tolerance and antinociception, and suggests that combined drugs can prevent tolerance and enhance fentanyl's pain-relieving effects. The findings have promising implications for chronic pain management.