Morphine analgesia and acute physical dependence: rapid onset of two opposing, dose-related processes.
Enhanced responsiveness to noxious stimulation is a reliable sign of opioid withdrawal and is therefore a measure of physical dependence. In lightly anesthetized rats, naloxone, given i.v. 15 min following i.v. morphine, caused a significant shortening of tail flick latency (hyperalgesia). At each dose of naloxone (0.1, 1.0 or 2.0 mg/kg), the magnitude of the observed hyperalgesia was a function of the preceding dose of morphine (0.5, 1.0 or 2.0 mg/kg). Thus morphine rapidly induces two dose-related opposing processes: one results in antinociception and the other in the potential for hyperalgesia.
Kim
D H
DH
Department of Neurosurgery, University of California, San Francisco 94143.
Fields
H L
HL
Barbaro
N M
NM
D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D010146:Pain / Q000378:metabolism* / Q000503:physiopathology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology*; D019966:Substance-Related Disorders / Q000503:physiopathology*
D000700:Analgesics; D011957:Receptors, Opioid; D009270:Naloxone; D009020:Morphine