title: Effects of naloxone and post-tetanic stimulation on isolated guinea-pig ileum followed by long exposure to morphine and bestatin.
abstract: This study was performed to compare the effects of naloxone (NLX) and post-tetanic stimulation on isolated guinea-pig ileum followed by prolonged exposure to morphine and bestatin. Morphine or bestatin alone did not induce any responses. In the presence of 1 microM morphine, the challenge with 1 microM naloxone caused quick contraction and post-tetanic contraction. A longer duration of these NLX-induced contraction and post-tetanic contractions was observed at the 6th stimulation compared to those after the 2nd stimulation. By contrast, the addition of bestatin, an aminopeptidase inhibitor, did not induce any NLX-induced contraction, although the same results for post-tetanic contraction as those of morphine were observed. These different effects of morphine and bestatin on NLX-induced contraction and post-tetanic contraction in the ileum may be due to different mechanisms of action in the opioid system. That in turn may suggest the possibility that bestatin has a physical dependence liability.
authors.affiliation: Institute of Experimental Animals, Department of Toxicology, Niigata College of Pharmacy, 5-13-2 Kamishin'ei-cho, Niigata-City, Niigata 950-2076, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Ozaki
mesh_terms: D000818:Animals; D004338:Drug Combinations; D004558:Electric Stimulation; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000503:physiopathology; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D011897:Random Allocation; D013746:Tetany / Q000503:physiopathology
chemical_list: D004338:Drug Combinations; D009292:Narcotic Antagonists; D009270:Naloxone; D009020:Morphine; D007930:Leucine; C012211:ubenimex