Hexarelin (GHS-R agonist) combined with morphine attenuated analgesic tolerance development and enhanced pain relief in rats, while the GHS-R antagonist had no significant effect.
Attenuated tolerancehexarelin combined with morphine slowed analgesic tolerance development in multiple pain tests
What the researchers found
Hexarelin (0.2 mg/kg) combined with morphine attenuated analgesic tolerance and enhanced antinociception in tail-flick and hot-plate tests. The GHS-R antagonist [d-Lys3]-GHRP-6 showed no significant effect on morphine tolerance.
Why it matters
Morphine tolerance forces dose escalation, increasing side effects and addiction risk. A peptide that can maintain morphine's effectiveness at lower doses could improve pain management while reducing opioid-related harms.
The numbers in context
104 rats; hexarelin attenuated morphine tolerance; [D-Lys3]-GHRP-6 had no effect; tested by tail-flick and hot plate.
How the study worked
104 Wistar rats. Three-day cumulative morphine dosing regimen to induce tolerance. Day 4 assessment of tolerance with hexarelin, GHS-R antagonist, and morphine combinations. Tail-flick and hot-plate analgesic tests at 30-min intervals.
Who was studied
Male Wistar rats (250-300g) in morphine tolerance models
What this study cannot tell us
Acute tolerance model in rats — may not fully replicate chronic tolerance in human patients. Mechanism by which hexarelin attenuates tolerance not fully elucidated. Clinical applicability and dosing for humans unknown.
How to read the evidence
Well-designed preclinical study with appropriate sample size (104 rats) and multiple analgesic outcome measures. Clinical translation needs further investigation.
When this study was published
Published in 2021. Ghrelin system modulation of opioid responses remains an active research area.
The bigger picture
The opioid crisis demands strategies to maintain analgesic efficacy while minimizing dose escalation. Ghrelin receptor activation represents a novel mechanism for achieving this, distinct from the traditional opioid receptor pathways targeted by most current approaches.
Questions still open
- Could hexarelin or similar GHS-R agonists be co-administered with opioids clinically to reduce tolerance?
- What is the mechanism by which ghrelin receptor activation modulates opioid tolerance?
- Would this approach also reduce other opioid side effects like respiratory depression?
Common questions
What is morphine tolerance?
How could a ghrelin receptor agonist help with pain?
Read the original research
Ghrelin receptor agonist hexarelin attenuates antinociceptive tolerance to morphine in rats.
Canadian journal of physiology and pharmacology, 99(5), 461-467
Citation
Baser, Tayfun; Ozdemir, Ercan; Filiz, Ahmet Kemal; Taskiran, Ahmet Sevki; Gursoy, Sinan. (2021). Ghrelin receptor agonist hexarelin attenuates antinociceptive tolerance to morphine in rats.. Canadian journal of physiology and pharmacology, 99(5), 461-467. https://doi.org/10.1139/cjpp-2020-0218