Spinal beta-endorphin analgesia involves an interaction with local monoaminergic systems.
beta-Endorphin administered intrathecally (i.t.) in rats produced a dose-dependent elevation in tail-flick latency. Naltrexone administered i.t. as a pretreatment reversed the spinal antinociceptive action of beta-endorphin, suggesting that the opioid interacts directly with spinal opiate receptors. Spinal administration of the alpha 1-adrenoceptor antagonist WB-4101 failed to alter the analgesic effects of the opioid, whereas the alpha 2-adrenoceptor antagonist yohimbine completely blocked beta-endorphin-induced elevations in tail-flick latency. Thus, there is an apparent specificity for the alpha 2-adrenoceptor to mediate the spinal action of beta-endorphin. The 5-HT1 and 5-HT3 receptor antagonists (spiroxatrine and ICS 205-930, respectively) also reversed the analgesic effects of the opioid, while the 5-HT2 receptor antagonist ritanserin only partially blocked beta-endorphin-induced elevations in tail-flick latency. The present results suggest that beta-endorphin produces analgesia at the spinal level via an opiate receptor-mediated interaction with spinal monoaminergic nerve terminals.
Crisp
T
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Department of Pharmacology, Northeastern Ohio Universities College of Medicine, Rootstown 44272.
Stafinsky
J L
JL
Hess
J E
JE
Uram
M
M
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000700:Analgesics / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D015306:Biogenic Monoamines / Q000502:physiology*; D007278:Injections, Spinal; D008297:Male; D009271:Naltrexone / Q000494:pharmacology; D009638:Norepinephrine / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000502:physiology; D012702:Serotonin Antagonists / Q000494:pharmacology; D013116:Spinal Cord / Q000187:drug effects*; D001615:beta-Endorphin / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D000317:Adrenergic alpha-Antagonists; D000700:Analgesics; D015306:Biogenic Monoamines; D012702:Serotonin Antagonists; D012701:Serotonin; D009271:Naltrexone; D001615:beta-Endorphin; D009638:Norepinephrine