Preferential action of eptazocine, a novel analgesic, with opioid receptors in isolated guinea pig ileum and mouse vas deferens preparations

• Published in: Nihon yakurigaku zasshi Vol. 95; no. 1; p. 41
• Main Authors: Tamura, T, Ogawa, J, Taniguchi, T, Waki, I
• Format: Journal Article
• Language: Japanese
• Published: Japan 01.01.1990
• Subjects: Analgesics - pharmacology; Animals; Cyclazocine - analogs & derivatives; Cyclazocine - antagonists & inhibitors; Cyclazocine - pharmacology; Electric Stimulation; Endorphins - pharmacology; Guinea Pigs; Ileum - drug effects; In Vitro Techniques; Male; Mice; Muscle Contraction - drug effects; Muscle, Smooth - drug effects; Receptors, Opioid - drug effects; Vas Deferens - drug effects
• ISSN: 0015-5691
• DOI: 10.1254/fpj.95.1_41

Actions of eptazocine, a novel analgesic, on isolated smooth muscle preparations were investigated. Eptazocine (10(-5) M) slightly inhibited electrically-driven twitch-tension in guinea pig ileum preparations sensitive to mu- and kappa-agonists, and this effect was antagonized by 10(-7) M naloxone. Eptazocine (10(-5)-10(-4) M) inhibited such an effect by the mu-agonist morphine. In mouse vas deferens preparations having delta-, mu- and kappa-receptors, eptazocine (10(-7) M-) inhibited the twitch-tension in a dose-dependent manner, being hardly inhibited by naloxone. On the other hand, MR-2266 (10(-6) M), a relatively selective kappa-receptor antagonist, inhibited the eptazocine effect. The Ke (equilibrium dissociation constant) value of naloxone against eptazocine was 325 nM and the Ke value of MR-2266 against eptazocine was 33.2 nM, showing that MR-2266 was 9.79-fold more effective than naloxone. These results suggest that eptazocine acted as a mu-receptor antagonist and as a kappa-receptor preferential agonist in isolated smooth muscle preparations.