We previously reported that morphine inhibits macrophage-colony stimulating factor (M-CSF)-induced proliferation of mouse bone marrow cells, both in vivo and in vitro, in a dose-dependent manner. We now report that either dynorphin A-(1-13) or dynorphin A-(1-10) amide, though having no effect on proliferation by themselves at concentrations less than 0.1 mM, can block the inhibitory effect of morphine both in vivo and in vitro, in a dose-dependent manner. The opioid antagonist naloxone can also block morphine's inhibitory effect on bone marrow cell proliferation in vivo, but has no effect in vitro. Dynorphin A-(1-13) was also able to block the dramatic reduction of spleen weight observed in animals chronically treated with morphine. Thus dynorphin, which has previously been shown to antagonize morphine analgesia, is also able to antagonize some of the immunosuppressive effects of morphine.
Bibliographical noteFunding Information:
This work was supported by NIDA Research Grants DA06011 (N.M.L.) and DA00564 (H.H.L.). and by Research Scientist Awards DA-00020 (N.M.L.) and DA-70554 (H.H.L.). We thank Drs. Andrew Smith and S. Ramakrishnan for critical comments.
- Bone marrow cells
- M-CSF (macrophage-colony stimulating factor)