Open AccessPartial agonistic action of morphine in the rat vas deferens.
Author(s) -
Kunio Ishii,
Satoshi Yamamoto,
Takamura Muraki,
Ryuichi Kato
Publication year - 1981
Publication title -
japanese journal of pharmacology/japanese journal of pharmacology
Language(s) - English
Resource type - Journals
eISSN - 1347-3506
pISSN - 0021-5198
DOI - 10.1254/jjp.31.905
Subject(s) - vas deferens , morphine , contraction (grammar) , agonist , potency , (+) naloxone , partial agonist , endocrinology , medicine , antagonist , chemistry , receptor , in vitro , biochemistry
Effects of morphine on the force of contraction of rat vas deferens were investigated. Morphine and beta-endorphin decreased the electrically evoked twitch tension, in a dose dependent manner. The inhibitory effect of morphine, however, was much weaker than that of beta-endorphin. These effects of both morphine and beta-endorphin were completely antagonized by naloxone. In the presence of 30 microM morphine, the dose-response curve of beta-endorphin shifted to the right by about 10-fold. Moreover, morphine partly reversed the contraction depressed by 0.3 microM beta-endorphin, in a dose dependent manner. These findings suggest that morphine acts as a partial agonist on the rat vas deferens. Marked tolerance to beta-endorphin and change in the antagonist potency of morphine were not observed in the vas deferens isolated from morphine-dependent rats.