Analgesia induced by intrathecal injection of dynorphin B in the rat.
A dose-dependent analgesic effect of intrathecally injected dynorphin B was observed in rats using the tail flick as nociceptive test. Intrathecal injection of 20 nmol of dynorphin B increased the tail flick latency by 90 +/- 23%, an effect that lasted about 90 min. For the same degree of analgesia, dynorphin B was 50% more potent than morphine on a molar basis. The analgesic effect of this dose of dynorphin B was partially blocked by 10 mg/kg, but not by 1 mg/kg, of subcutaneous naloxone, showing a relative resistance to naloxone reversal as compared with morphine analgesia. The analgesia produced by dynorphin B was unchanged in morphine-tolerant rats but was significantly decreased in rats tolerant to ethylketazocine. These results suggest that dynorphin B produces its potent analgesic effect by activation of kappa rather than mu opioid receptors in the rat spinal cord.
D000700:Analgesics; D000818:Animals; D003496:Cyclazocine / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D004399:Dynorphins; D004723:Endorphins; D004743:Enkephalin, Leucine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D016314:Ethylketocyclazocine; D005260:Female; D007278:Injections, Spinal; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D051381:Rats
D000700:Analgesics; D004723:Endorphins; D009270:Naloxone; D016314:Ethylketocyclazocine; D004743:Enkephalin, Leucine; D004399:Dynorphins; D009020:Morphine; C036200:rimorphin; D003496:Cyclazocine