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The contribution of intrinsic activity to the action of opioids in vitro
Author(s) -
Miller Lynne,
Shaw J.S.,
Whiting Elaine M.
Publication year - 1986
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.1476-5381.1986.tb10202.x
Subject(s) - vas deferens , agonist , potency , receptor , partial agonist , medicine , chemistry , endocrinology , intrinsic activity , pharmacology , guinea pig , morphine , ileum , in vitro , biology , biochemistry
1 The effects of opioids were compared in five field‐stimulated isolated tissue models, the guinea‐pig ileum and vasa deferentia from rat, rabbit and mice of the Alderley Park and C57BL/6 strains. 2 Although the μ‐receptor agonist [D‐Ala 2 , MePhe 4 , Gly‐ol 5 ] enkephalin appeared to act at similar receptors in the guinea‐pig ileum, rat vas deferens, mouse vas deferens and C57BL/6 mouse vas deferens preparations, its potency varied considerably between these preparations. Similar potency differences were also observed with the k‐agonist, ethylketocyclazocine. 3 It is proposed that these variations in potency reflect differences in the number of spare receptors present in each model. The finding that some drugs which have agonist activity in the more sensitive preparations behave as antagonists in the less sensitive tissues supports this proposal and highlights the importance of intrinsic activity in determining the action of opioids. 4 Many of the prototypic opioid agonists were found to be either partial agonists (eg. morphine and bremazocine) or to possess affinity for more than one receptor type (eg. ethylketocyclazocine, Mr 2034).