Morphine-tolerant longitudinal muscle strip from guinea-pig ileum.
1. Implantation of morphine pellets in guinea-pigs produced a high degree of tolerance and dependence within 3 days.2. The contractions of the longitudinal muscle induced by electrical stimulation of the myenteric plexus-longitudinal muscle preparations obtained from tolerant animals were less depressed by morphine than the contractions evoked in preparations from non-tolerant animals.3. Naloxone did not alter the size of the evoked twitch but antagonized the depressant action of morphine in tolerant and in non-tolerant animals. When given to tolerant guinea-pigs, naloxone caused an increase in intestinal activity in vivo.4. The contractile response of the longitudinal muscle to acetylcholine was the same in preparations obtained from tolerant and non-tolerant animals. Electrically evoked contractions of the myenteric plexus-longitudinal muscle preparations from tolerant animals showed reduced sensitivity to the depressant effects of adrenaline, isoprenaline, and particularly, dopamine.
D000818:Animals; D004298:Dopamine / Q000494:pharmacology; D004361:Drug Tolerance; D004558:Electric Stimulation; D004837:Epinephrine / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D007082:Ileum / Q000187:drug effects*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D019966:Substance-Related Disorders
D009270:Naloxone; D009020:Morphine; D007545:Isoproterenol; D004298:Dopamine; D004837:Epinephrine