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Release of immunoreactive Met-enkephalin from the spinal cord by intraventricular beta-endorphin but not morphine in
Abstract:
Effect of beta-endorphin and morphine injected intraventricularly on the release of immunoreactive Met-enkephalin, Leu-enkephalin and dynorphin1-13 from the spinal cord was studied in anesthetized rats. Intraventricular beta-endorphin, 16 micrograms, caused a marked spinal release of immunoreactive Met-enkephalin and to a much lesser extent, of immunoreactive Leu-enkephalin while intraventricular morphine, 40 micrograms, did not cause any significant release of immunoreactive enkephalins. The release of immunoreactive Met-enkephalin was not blocked by the pretreatment with 5 mg/kg naloxone, i.p. Immunoreactive dynorphin1-13 was not released by either beta-endorphin or morphine. High performance liquid chromatographic analysis indicated that immunoreactive Met-enkephalin released by beta-endorphin had a retention time identical to [3H]Met-enkephalin. These findings in conjunction with previous pharmacological studies suggest different modes of pharmacological action for beta-endorphin and morphine.
Insights
Intraventricular beta-endorphin, but not morphine, significantly increased spinal Met-enkephalin release in rats. This suggests distinct pharmacological actions for these opioids on the central nervous system.
Area of Science:
- Neuroscience
- Pharmacology
- Neuroendocrinology
Background:
- Opioid peptides like endorphins and enkephalins play crucial roles in pain modulation.
- Understanding the differential release of endogenous opioids is vital for developing targeted pain therapies.
Purpose of the Study:
- To investigate the effects of intraventricular beta-endorphin and morphine on spinal opioid peptide release.
- To compare the release patterns of Met-enkephalin, Leu-enkephalin, and dynorphin1-13.
Main Methods:
- Anesthetized rats received intraventricular injections of beta-endorphin or morphine.
- Spinal cord release of immunoreactive Met-enkephalin, Leu-enkephalin, and dynorphin1-13 was measured.
- High-performance liquid chromatography (HPLC) was used to confirm peptide identity.
Main Results:
- Intraventricular beta-endorphin induced significant spinal release of Met-enkephalin and, to a lesser extent, Leu-enkephalin.
- Intraventricular morphine did not cause a significant release of immunoreactive enkephalins.
- Naloxone pretreatment did not block the Met-enkephalin release induced by beta-endorphin.
- Neither beta-endorphin nor morphine affected dynorphin1-13 release.
Conclusions:
- Beta-endorphin and morphine exhibit different mechanisms of action regarding spinal opioid peptide release.
- Beta-endorphin stimulates the release of endogenous enkephalins, suggesting a distinct pathway compared to morphine.