Presynaptic opioid receptor subtypes in the rabbit ear artery
Illes, P.; Pfeiffer, N.; von Kügelgen, I.; Starke, K.
Journal of Pharmacology and Experimental Therapeutics 232(2): 526-533
1985
ISSN/ISBN: 0022-3565 PMID: 2982015 Document Number: 247939
In segments of rabbit ear arteries preincubated with noradrenaline, normorphine, fentanyl and morphiceptin did not change the vasoconstrictor response (5 pulses/min, 5 Hz, 0.3 msec pulse duration). Among various peptide agonists, Leu-enkephalin, D-Ala2-D-Leu-enkephalin and Met-enkephalin were the most potent inhibitors. In a series of peptides with C-terminal extensions of the Met-enkephalin chain, the potency decreased in the order Met-enkephalin > Met-enkephalin-Arg-Gly-Leu > Met-enkephalin-Arg-Phe > BAM-12P > .beta.-endorphin. In a series of peptides with C-terminal extensions of the Leu-enkephalin chain, the potency decreased in the order Leu-enkephalin > dynorphin1-13 > dynorphin1-9 > .alpha.-neo-endorphin > dynorphin1-6 > dynorphin1-6 > dynorphin1-17. The .DELTA. selective antagonist ICI 154129 counteracted the effect of Met-enkephalin but not that of dynorphin1-13, whereas naloxone counteracted the effect of either agonist. Given alone, high concentrations of naloxone and ICI 154129 as well as of the opioid antagonist (.sbd.)-MR 2266 (but not the nonantagonistic enantiomer (+)-MR 2267) enhanced the vasoconstrictor response. Naloxone and (.sbd.)-MR 2266 also enhanced the vasoconstriction elicited by exogenous noradrenaline, whereas Met-enkephalin selectively inhibited the response to electrical nerve stimulation. The postganglionic sympathetic neurons innervating the rabbit ear artery possess presynaptic opioid receptors of the .beta.- and .kappa.-, but not of the .mu.-types. The receptors do not appear to be targets of coreleased endogenous opioid peptides under the conditions of these experiments.