Analgesic cross-tolerance between morphine and opioid peptides

✍ Scribed by Subbiah P. Sivam; Ing K. Ho

• Book ID: 104771605
• Publisher: Springer
• Year: 1984
• Tongue: English
• Weight: 221 KB
• Volume: 84
• Category: Article
• ISSN: 0033-3158
• DOI: 10.1007/bf00432026

✦ Synopsis

The analgesic effect of intracerebroventricular administration of morphine, ketocyclazocine, [D-ala2]-methionine enkephalinamide (DAM), [D-ala2-D-leuS]-enkephalin (DADLE), leuenkephalin, metenkephalin, and /3-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 (EDs0 , nmol) was/3-endorphin > morphine = DAM > DADLE > ketocyclazocine = leuenkephalin = metenkephalin. The morphine-tolerant animals were cross-tolerant to ketocyclazocine and to all the peptides studied; DAM and fl-endorphin exhibited the highest degree of tolerance. In morphine-tolerant animals, the order of potency was morphine = DADLE = fl-endorphin > DAM = ketocyclazocine = metenkephalin > leuenkephalin. The results indicate that endogenous opioid systems may be affected by tolerance development to morphine.