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Age-dependent morphine tolerance development in the rat.

Yan Wang1, James Mitchell, Kumi Moriyama

  • 1Department of Anesthesia and Perioperative Care, University of California, San Francisco.

Anesthesia and Analgesia
|May 28, 2005
PubMed
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Younger rats develop morphine tolerance faster than older rats. This age-related difference in opioid tolerance is not due to metabolism, suggesting other molecular factors are involved.

Area of Science:

  • Pharmacology
  • Neuroscience
  • Gerontology

Background:

  • Opioid use for chronic pain is increasing across all age groups.
  • The influence of age on the development of opioid tolerance remains poorly understood.
  • Understanding age-related differences in tolerance is crucial for effective pain management.

Purpose of the Study:

  • To investigate age-related variations in morphine tolerance development in a rat model.
  • To determine if pharmacokinetic differences contribute to age-dependent tolerance.
  • To identify potential molecular targets for modulating opioid tolerance.

Main Methods:

  • Utilized rats of four age groups: 3 weeks, 3 months, 6 months, and 1 year.
  • Administered morphine (8 mg/kg) subcutaneously twice daily.

Related Experiment Videos

  • Assessed analgesic effect via tail-flick latency using thermal stimuli.
  • Defined tolerance as a 75% reduction in morphine-induced analgesia.

    • Main Results:

    • Younger rats (3 weeks) developed tolerance most rapidly (Day 4).
    • Older rats (1 year) showed the slowest tolerance development (Day 22).
    • Plasma morphine levels and metabolites did not correlate with observed tolerance differences.

    Conclusions:

    • Morphine tolerance develops significantly faster in younger rats compared to older rats.
    • Pharmacokinetic factors (metabolism, clearance) do not explain these age-related differences.
    • Aging likely influences molecular pathways of tolerance, offering potential therapeutic targets.