Selective receptors for beta-endorphin on the rat vas deferens. |
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Authors: | R Schulz E Faase M Wüster A Herz |
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Affiliation: | 1. Department of Neuropharmacology, Max-Planck-Institut für Psychiatrie, Kraepelinstrasse 2, 8000 München 40, Federal Republic of Germany |
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Abstract: | The isolated rat vas deferens, being insensitive to morphine, contains selective binding sites for β-end-orphin. A half-maximal inhibition of twitch tension evoked by electrical stimulation is established with 100 nM β-endorphin, while fragments of β-endorphin, that is, methionine-enkephalin, α- and γ-endorphin, are almost ineffective. The opiate alkaloid etorphine, a powerful inhibitor of guinea-pig ileum and mouse vas deferens, is 100-fold less potent on the rat vas deferens. The unique β-endorphin activity suggests very specific binding sites for this peptide, which cannot be related to the μ- or δ-receptors so far described for opiods on isolated preparations. |
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