Differential migratory properties of mouse, fish, and frog leukocytes treated with agonists of opioid receptors.

Zymosan-induced peritoneal inflammation was inhibited by morphine co-injection in mice and fish but not in anuran amphibians. In present experiments, an in vitro migration of mouse, goldfish, and frog leukocytes to L15 medium, control serum (S) or zymosan-activated serum (ZAS) was recorded following cell preincubation with L15 or with agonists of mu, delta, or kappa opioid receptors (morphine, deltorphine, or U-50,488H, respectively). In all species, migration of control leukocytes was in the order ZAS > S > L15. Pretreatment with morphine or deltorphine (but not with U-50,488H) enhanced leukocyte migration to L15 and S in each species, while it inhibited migration of mouse and fish (but not frog) leukocytes to ZAS, phenomena reversed by specific antagonists of mu and delta opioid receptors (CTOP or naltrindole, respectively). It seems that final effects of opioids on cell migration are dependent on a species-specific balance between up- and down-regulation of leukocyte migration resulted from interplay between receptors for opioids and chemotactic factors.