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Relationship between analgesia and respiratory depression for mu opioid receptor agonists in mice
1Department of Anaesthesia, University of Manchester.
Abstract:
The relationship between analgesic activity, measured as the hot plate reaction time, and respiratory depression, measured as ventilatory frequency, was investigated in mice for a variety of mu opioid receptor agonists with differing selectivities for mu receptors compared with delta receptors. There was a weak correlation between analgesia and respiratory depression for opioids with the greatest selectivity for mu opioid receptors compared with delta receptors, such as alfentanil. The strength of the correlation increased for opioids which had greater delta receptor activity, such as morphine and fentanyl. Etorphine, which has almost equal affinity for mu, delta and, incidentally, kappa receptors, showed a strong correlation between analgesia and respiratory depression. We conclude that the predictability of the degree of respiratory depression produced by a given analgesic dose of an opioid appears to decrease with its selectivity for mu opioid receptors, at least in the mouse.
Insights
Opioid selectivity for mu receptors impacts pain relief versus breathing side effects. Highly selective mu agonists show weak correlation, while mixed agonists show stronger links between analgesia and respiratory depression in mice.
Area of Science:
- Pharmacology
- Neuroscience
- Pain Research
Background:
- Opioid analgesics are crucial for pain management.
- Respiratory depression is a significant side effect of opioids.
- Understanding the relationship between analgesia and respiratory depression is vital for opioid safety.
Purpose of the Study:
- To investigate the correlation between analgesic activity and respiratory depression in mice.
- To examine how mu-opioid receptor selectivity influences this relationship.
- To compare different mu-opioid receptor agonists based on their receptor selectivity profiles.
Main Methods:
- Utilized hot plate test to measure analgesic activity (reaction time).
- Measured respiratory depression via ventilatory frequency in mice.
- Administered various mu-opioid receptor agonists with differing mu vs. delta receptor selectivities.
Main Results:
- Opioids highly selective for mu-opioid receptors (e.g., alfentanil) showed a weak correlation between analgesia and respiratory depression.
- Increased delta-receptor activity (e.g., morphine, fentanyl) strengthened this correlation.
- Etorphine, with balanced mu, delta, and kappa receptor affinity, demonstrated a strong correlation.
Conclusions:
- Predictability of opioid-induced respiratory depression decreases with increased mu-opioid receptor selectivity.
- Receptor selectivity profile significantly influences the balance between pain relief and respiratory side effects.
- Findings suggest caution when using highly mu-selective opioids, as respiratory depression may be less predictable.