Studies on the intrathecal effect of beta-endorphin in primate.
The intrathecal administration of beta-endorphin in the primate through an indwelling spinal catheter, produced a significant elevation in the nociceptive threshold as measured by the discrete trial shock titration task. The time of onset, duration of effect and magnitude of effect were all dose-dependent over a range of 150-750 micrograms. The effects were antagonized in a dose-dependent fashion by the systemic administration of naloxone. Aside from the elevations in the shock titration threshold produced by intrathecal beta-endorphin, no untoward effects on the animal's motor function or behavioral reactivity was noted. Significantly, unlike morphine, intrathecal beta-endorphin failed to produce any signs of scratching behavior at the doses used in these experiments. Once daily administration of intrathecal beta-endorphin (500 micrograms) showed a significant progressive decline in the antinociceptive effect over an 8-day period. Animals made tolerant to beta-endorphin in this fashion showed a significantly reduced response to an otherwise active dose of intrathecal morphine, indicating evidence for cross tolerance.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D004723:Endorphins / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D007278:Injections, Spinal; D008253:Macaca mulatta; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology; D010100:Oxygen / Q000097:blood; D001615:beta-Endorphin
D004723:Endorphins; D002245:Carbon Dioxide; D009270:Naloxone; D001615:beta-Endorphin; D010100:Oxygen