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Changes in opioid receptor density on murine splenocytes induced by in vivo treatment with morphine and methadone
G Patrini1, P Massi, G Ricevuti
1Institute of Pharmacology, Faculty of Sciences, University of Milan, Italy.
Abstract:
In a 24-hr time course study we reported previously that a single systemic injection of morphine profoundly affected various immune parameters in mice. In the present study we examined whether these effects are mediated by changes in opioid receptor density on murine splenocytes after acute in vivo morphine (20 mg/kg s.c.) and methadone (12.5 mg/kg s.c.) at equianalgesic doses. To define the splenocyte subpopulations we used flow cytofluorimetric analysis with specific fluorescent monoclonal antibodies and calculated the binding of the fluoresceinyl opiate antagonist naloxone on opiate receptors. Both morphine and methadone reduced the density of opiate receptors on B- and T-lymphocytes. Specifically, 20 min, 1 and 3 days after the injection there was a marked reduction (about 55%) in naloxone binding sites; these returned to base line after 5 days for T-lymphocytes and after 7 days for B-lymphocytes. Despite the low proportion of macrophages among total splenocytes (about 10%), our results also indicate a tendency to a reduction in opiate receptor density also in the macrophage population. These findings indicate that a single exposure to morphine and methadone results in a strong, lasting down-regulation of opiate binding sites in murine splenocytes, probably accounting for the immunomodulation induced by opiates.
Insights
Single doses of morphine and methadone significantly reduce opioid receptor density on mouse immune cells, likely explaining their immunomodulatory effects. Receptor levels gradually return to normal over several days.
Area of Science:
- Immunology
- Neuroscience
- Pharmacology
Background:
- Previous research indicated that a single morphine injection impacts immune parameters in mice.
- Opioid drugs are known to affect the immune system, but the underlying mechanisms involving receptor density changes require further investigation.
Purpose of the Study:
- To investigate if changes in opioid receptor density on murine splenocytes mediate the immunomodulatory effects of acute in vivo morphine and methadone administration.
- To quantify the alterations in opioid receptor density on specific splenocyte subpopulations following opioid exposure.
Main Methods:
- Utilized flow cytofluorimetric analysis to identify splenocyte subpopulations (B-cells, T-cells, macrophages).
- Measured the binding of fluoresceinyl opiate antagonist naloxone to quantify opiate receptor density.
- Administered equianalgesic doses of morphine (20 mg/kg s.c.) and methadone (12.5 mg/kg s.c.) to mice.
Main Results:
- Both morphine and methadone significantly reduced opiate receptor density on B- and T-lymphocytes by approximately 55% within 20 minutes to 3 days post-injection.
- Opiate receptor density on T-lymphocytes returned to baseline levels after 5 days, while B-lymphocytes recovered after 7 days.
- A trend towards reduced opiate receptor density was observed in macrophages, despite their lower proportion in splenocytes.
Conclusions:
- Acute administration of morphine and methadone induces a substantial and prolonged down-regulation of opiate binding sites on murine splenocytes.
- This down-regulation of opioid receptors likely contributes to the observed immunomodulatory effects of these opioid analgesics.