Analgesic cross-tolerance between morphine and opioid peptides

Subbiah P. Sivam, Ing K. Ho

Research output: Contribution to journalArticle

9 Scopus citations


The analgesic effect, of intracerebroventricular administration of morphine, ketocyclazocine, [D-ala2]-methionine enkephalinamide (DAM), [D-ala2-D-leu5]-enkephalin. (DADLE), leuenkephalin, metenkephalin, and β-endorphin on acetic acid-induced abdominal writhing (AAW) was investigated in naive and morphine-tolerant mice. It was found that the relative potencies of a series of opioids are different in naive and morphine-tolerant groups. In naive animals, the order of potency (ED50, nmol) was β-endorphin > morphine=DAM > DADLE > ketocyclazocine=leuenkephalin=metenkephalin. The morphine-tolerant animals were cross-tolerant to ketocyclazocine and to all the peptides studied; DAM and β-endorphin exhibited the highest degree of tolerance. In morphine-tolerant animals, the order of potency was morphine=DADLE=β-endorphin > DAM=ketocyclazocine =metenkephalin > leuenkephalin. The results indicate that endogenous opioid systems may be affected by tolerance development to morphine.

Original languageEnglish (US)
Pages (from-to)64-65
Number of pages2
Issue number1
StatePublished - Sep 1 1984
Externally publishedYes


  • Morphine
  • Opiates
  • Opioid peptides
  • Tolerance

ASJC Scopus subject areas

  • Pharmacology

Fingerprint Dive into the research topics of 'Analgesic cross-tolerance between morphine and opioid peptides'. Together they form a unique fingerprint.

  • Cite this