The antinociceptive effects of epidural opiates in the cat: studies of the pharmacology and the effects of lipophilicity in spinal analgesia.
In cats implanted chronically with catheters in the lumbar epidural space, the pharmacology of the analgesia of 4 opiates, which varied widely in their physicochemical properties, was studied. Results revealed the following order of epidural analgesic potency as indicated by suppression of the spinally mediate skin twitch reflex: lofentanyl greater than morphine greater than L-methadone greater than meperidine greater than D-methadone. With the doses used in these experiments the duration of action was: morphine greater than lofentanyl greater than L-methadone = meperidine. In addition, antagonism of these effects by systemic naloxone and the development of tolerance after daily epidural administration of morphine were demonstrated. These data, jointly, indicate a specific receptor mechanism of action. We suggest that this animal model may be useful for the evaluation of new opiates and non-opiates to be given via the epidural route.
D000818:Animals; D002415:Cats; D004305:Dose-Response Relationship, Drug; D004824:Epidural Space; D005260:Female; D005283:Fentanyl / Q000031:analogs & derivatives / Q000494:pharmacology; D008055:Lipids; D008297:Male; D008614:Meperidine / Q000494:pharmacology; D008691:Methadone / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009294:Narcotics / Q000627:therapeutic use*; D009619:Nociceptors / Q000187:drug effects*; D010146:Pain / Q000188:drug therapy*; D012018:Reflex / Q000187:drug effects; D012867:Skin / Q000294:innervation; D013997:Time Factors
D008055:Lipids; D009294:Narcotics; D009270:Naloxone; D009020:Morphine; C034846:lofentanil; D008614:Meperidine; D008691:Methadone; D005283:Fentanyl