The role of opiate receptors in the potentiation of pentobarbital sleeping time by the acute and chronic administration of opiates.
Male rats injected with pentobarbital (50.0 mg/kg i.p.) showed increased sleeping time after the acute administration of morphine (5.0 or 10.0 mg/kg s.c.). This effect was antagonized by naltrexone (2.0 mg/kg s.c.). The enhancement displayed stereoselectivity as levorphanol greatly lengthened the sleeping time induced by pentobarbital while dextrophan only produced a slight increase. Rats implanted for 3 days with pellets of morphine base (75.0 mg) were tolerant to the analgesic effects of morphine (2.5 mg/kg s.c.) but showed an even greater increase in pentobarbital-induced sleeping time than rats treated acutely. No potentiation was observed in subjects that were also implanted with a pellet of naltrexone (30.0 mg). It is concluded that the potentiation of pentobarbital-induced sleeping time produced by opiates is mediated by opiate receptors, but fails to show the development of tolerance.
Pechnick
R N
RN
Department of Pharmacology, School of Medicine, U.C.L.A. 90024.
Terman
G W
GW
D000818:Animals; D003917:Dextrorphan / Q000494:pharmacology; D004357:Drug Synergism; D007981:Levorphanol / Q000494:pharmacology; D008297:Male; D009271:Naltrexone / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D010424:Pentobarbital / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects*; D012890:Sleep / Q000187:drug effects*; D013237:Stereoisomerism; D013997:Time Factors
D009294:Narcotics; D011957:Receptors, Opioid; D003917:Dextrorphan; D007981:Levorphanol; D009271:Naltrexone; D010424:Pentobarbital