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INTERACTIONS OF DRUGS ACTIVE AT OPIATE RECEPTORS AND DRUGS ACTIVE AT α 2 ‐RECEPTORS ON VARIOUS TEST SYSTEMS
Author(s) -
BROWNING S.,
LAWRENCE D.,
LIVINGSTON A.,
MORRIS B.
Publication year - 1982
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1982.tb09322.x
Subject(s) - receptor , pharmacology , opiate receptors , opiate , medicine , chemistry , neuroscience , biology , opioid , (+) naloxone
1 The actions of the opiate receptor drugs, morphine, methionine‐enkephalin (Met‐enkephalin) and naloxone were compared with the actions of the α 2 ‐receptor drugs, clonidine, xylazine and yohimbine on analgesic tests, in vitro bioassay (guinea‐pig ileum and mouse vas deferens), and radioligand displacement studies on rat brain membrane preparations. 2 Both opiate and α 2 ‐agonist drugs showed analgesic activity but whilst the α 2 ‐agonist analgesic activity was antagonized by only α 2 ‐antagonists, the analgesic activity of morphine was antagonized by both naloxone and yohimbine. In the in vitro tests, both groups of agonists inhibited electrically evoked activity; however in these experiments only antagonism of opiates by naloxone and α 2 ‐agonists by yohimbine could be shown and it is concluded that in these systems the activity of the α 2 ‐agonists is mediated via the presynaptic α 2 ‐receptors only. 3 In the radioligand studies the drugs acting at α 2 ‐receptors were active in the micromolar range at displacing labelled opioid ligands but opiates did not displace labelled α 2 ‐ligands. 4 It is concluded that drugs which act on α 2 ‐receptors interfere with the in vivo analgesic effects of opiates and weakly displace opioid radioligand binding, but opioids do not affect α 2 agonist analgesia and do not appear to displace α 2 ‐agonist radioligand binding.