Quantification of the analgesic activity of narcotic antagonists by a modified hot-plate procedure.
The analgesic activity of morphine and the narcotic antagonists, pentazocine, cyclazocine, levallorphan and nalorphine, was assessed in the rat using two hot plates: one maintained at 49.5 degrees C and the other at the "standard" 54.5 degrees C. The analgesic effects of morphine using the 49.5 degrees C hot plate were of a significantly greater magnitude than its effects using the 54.5 degrees C hot plate for both nontolerant and morphine-tolerant subjects. Dose-related effects were observed with all of the narcotic antagonists tested using the 49.5 degrees C hot plate; only the highest dose of pentazocine exhibited activity using the 54.5 degrees C hot plate. Naloxone (3.0 mg/kg) antagonized the analgesic effects of morphine and all of the narcotic antagonists, but was without activity itself when tested using the 49.5 degrees C hot plate at doses as high as 30 mg/kg. Aspirin was also inactive using the 49.5 degrees C plate, whereas physostigmine increased latencies only at a dose that produced severe motor deficit. A low temperature hot plate is recommended for evaluating the analgesic activity of narcotic antagonists in the rat. This simple procedure provides results which are dose-related, quantifiable, reproducible, of a large magnitude and specific.
D000698:Analgesia; D000704:Analysis of Variance; D000818:Animals; D003496:Cyclazocine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D006358:Hot Temperature; D006801:Humans; D007977:Levallorphan / Q000494:pharmacology; D008297:Male; D008722:Methods; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D010423:Pentazocine / Q000494:pharmacology; D051381:Rats; D011930:Reaction Time / Q000187:drug effects; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology
D009292:Narcotic Antagonists; D007977:Levallorphan; D009270:Naloxone; D009020:Morphine; D003496:Cyclazocine; D010423:Pentazocine