Effects of nalbuphine, pentazocine and U50488H on gastric emptying and gastrointestinal transit in the rat |
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Authors: | Asai T; Mapleson W W; Power I |
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Institution: | Department of Anaesthesiology, Kansai Medical University, 10-15 Fumizono-cho, Moriguchi City, Osaka 570, Japan; Deparment of Anaesthetics and Intensive Care Medicine, University of Wales College of Medicine, Heath Park, Cardiff CF4 4XN; Department of Anaesthesia and Pain Management, Royal North Shore Hospital, and University of Sydney St Leonards, NSW 2065, Australia |
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Abstract: | We studied the effect of mixed agonist-antagonist opioids (nalbuphine and
pentazocine) and a kappa opioid agonist (U50488H) on gastric emptying and
gastrointestinal transit, and their interactions with morphine in rats. In
each group, nalbuphine (0.01-30 mg kg-1), pentazocine (1-30 mg kg-1),
U50488H (1-100 mg kg(-1)1) or saline was injected i.p. at 0 min. Another
four groups of rats received morphine 13.4 mg kg-1 (ED75) and one of the
following substances: saline, nalbuphine, pentazocine or U50488H. In both
groups, at 30 min, radiolabelled saline 1 ml was infused into the stomach;
at 1 h, gastric emptying and gastrointestinal transit were calculated by
measuring the radioactivity in the gastrointestinal tract. Slopes for
dose-response curves were determined. Nalbuphine significantly, but only
weakly, delayed gastric emptying (P < 0.0005) and gastrointestinal
transit (P < 0.01). Pentazocine markedly inhibited both, whereas U50488H
did not significantly inhibit either. The slopes of the dose-response
curves for nalbuphine, but not for pentazocine, on both gastric emptying
and gastrointestinal transit were significantly less steep than those for
morphine. Nalbuphine significantly antagonized the inhibitory effect of
morphine on gastric emptying (P = 0.005) and gastrointestinal transit (P =
0.02), whereas pentazocine and U50488H did not. Nalbuphine and pentazocine
delay gastric emptying and gastrointestinal transit, possibly by different
mechanisms.
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