Endogenous opioids and the growth regulation of a neural tumor

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Endogenous opioid systems (endogenous opioids and their receptors) are known to participate in the regulation of tumor growth. The present study was conducted to examine whether [Met5]-enkephalin influences the growth of transplanted neuroblastoma, and to explore the role of other opioid peptides in carcinogenesis. A/Jax mice were inoculated with 106 S20Y cells and received daily injections of [Met5]-enkephalin. Dosages of 0.5 to 30 mg/kg delayed tumor appearance and prolonged survival of these mice; antitumor effects were blocked by concomitant injections of naloxone. Daily administration (10 mg/kg) of [Leu5]-enkephalin had no effect on neurotumor growth. [D-Ala2, D-Leu5]-enkephalin and ethylketocyclazocine, ligands selective for delta and kappa receptors, respectively, also did not influence neuro-oncogenesis. These results demonstrated the potent growth inhibiting effects of the naturally occurring opioid pentapeptide, [Met5]-enkephalin, and substantiate reports identifying and characterizing an opioid receptor (i.e., zeta) for which [Met5]-enkephalin is the most potent ligand.

Original languageEnglish (US)
Pages (from-to)1313-1318
Number of pages6
JournalLife Sciences
Issue number16
StatePublished - 1988

All Science Journal Classification (ASJC) codes

  • General Pharmacology, Toxicology and Pharmaceutics
  • General Biochemistry, Genetics and Molecular Biology


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