title: Classification of presynaptic opioid receptors in the rabbit ear artery by competitive antagonists.
abstract: Electrical field stimulation (5 impulses at 5 Hz every min) evoked vasoconstriction in the rabbit isolated ear artery. The vasoconstriction was depressed by [Leu5]enkephalin (IC50 = 47 nM) and ethylketocyclazocine (IC50 = 80 nM). Naloxone 300 nM antagonized the effect of both agonists with a similar potency; the respective KB values were 41 and 64 nM. ICI 174864 1000 nM antagonized only the effect of [Leu5]enkephalin (KB = 126 nM) but not that of ethylketocyclazocine. In contrast, MR 2266 100 nM was a more potent antagonist of ethylketocyclazocine (KB = 8 nM) than of [Leu5]enkephalin (KB = 45 nM). The results suggest that the rabbit ear artery contains both presynaptic delta- and kappa-receptors.
mesh_terms: D000818:Animals; D001158:Arteries / Q000294:innervation*; D001575:Benzomorphans / Q000378:metabolism; D001667:Binding, Competitive; D001681:Biological Assay; D003496:Cyclazocine / Q000031:analogs & derivatives / Q000378:metabolism; D004423:Ear / Q000098:blood supply; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000378:metabolism; D016314:Ethylketocyclazocine; D066298:In Vitro Techniques; D009270:Naloxone / Q000378:metabolism; D011817:Rabbits; D011957:Receptors, Opioid / Q000145:classification* / Q000378:metabolism; D013570:Synaptic Membranes / Q000378:metabolism
chemical_list: D001575:Benzomorphans; D011957:Receptors, Opioid; D009270:Naloxone; C027247:MR 2266; D016314:Ethylketocyclazocine; D004743:Enkephalin, Leucine; C040643:N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine; D003496:Cyclazocine