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Updated: Sep 20, 2026

Gastrointestinal Motility Monitor (GIMM)
Published on: December 1, 2010
Decreased response to GABA-B agonists in longitudinal smooth muscle-myenteric plexus preparations from
S Luzzi1, S Franchi-Micheli, M Ciuffi
1Department of Preclinical and Clinical Pharmacology Mario Aiazzi Mancini, University of Florence, Italy.
Abstract:
1) Responsiveness of guinea-pig ileal longitudinal smooth muscle-myenteric plexus preparations to drugs activating GABA-B receptors was studied in morphine-tolerant animals. For this purpose morphine pellets (75 mg each) were implanted subcutaneously in guinea-pigs and experiments were performed three days later in electrically-stimulated ileal strips. 2) Activation of GABA-B receptors with GABA (10(-6) -10(-3) M) or (-)-baclofen (10(-6)-10(-3) M) caused a dose-related inhibition of twitch response that was about 80% lower in preparations from morphine-tolerant animals than in controls. This was found both in preparations maintained in the presence of morphine (10(-6) M) and in morphine-free Krebs. The effect was evident also in ileal preparations from morphine-tolerant animals in which a withdrawal syndrome was induced by the administration of naloxone before sacrifice. 3) The phenomenon was specific since the dose-response curve of the adenosine-inhibitory effect was comparable in preparations from tolerant animals and controls. 4) The hyporesponsiveness to GABA-B receptor activation began 12 h after pellet implantation and was maximal on the third day. 5) It is concluded that during tolerance to and withdrawal from morphine there is a hyporesponsiveness of GABA-B receptors in "in vitro" guinea-pig ileal longitudinal muscle-myenteric plexus preparations.
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