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Gastrointestinal Motility Monitor (GIMM)
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Published on: December 1, 2010

Effects of methylnaltrexone on guinea pig gastrointestinal motility

Laura Anselmi1, Jennifer Huynh, Gaia Vegezzi

  • 1CURE Digestive Diseases Research Center, Digestive Diseases Division, Department of Medicine, David Geffen School of Medicine, University of California Los Angeles, 11301 Wilshire Blvd., Los Angeles, CA 90073, USA. lauranselmi@yahoo.it

Naunyn-Schmiedeberg'S Archives of Pharmacology
|January 31, 2013
PubMed

Insights

Methylnaltrexone (MNTX) reverses opioid-induced gastrointestinal (GI) transit delays by acting on peripheral μ opioid receptors. MNTX does not affect GI motility in the absence of opioid stimulation.

Area of Science:

  • Pharmacology
  • Gastroenterology
  • Neuroscience

Background:

  • Opioid medications are widely used for pain management.
  • Opioid use can lead to significant gastrointestinal (GI) side effects, including constipation.
  • Methylnaltrexone (MNTX) is a peripherally acting μ opioid receptor (μOR) antagonist developed to counteract these effects.

Purpose of the Study:

  • To compare the effects of MNTX on GI motility in naïve versus chronically opiate-treated guinea pigs.
  • To investigate MNTX's efficacy in vitro and in vivo.
  • To determine if MNTX affects GI transit in the absence of opioid stimulation.

Main Methods:

  • In vitro: Electrically stimulated muscle twitch contractions of longitudinal muscle-myenteric plexus (LMMP) preparations.
  • In vivo: Measurement of total GI transit in guinea pigs.
  • Dose-response studies with MNTX and morphine in both naïve and chronically treated animals.

Main Results:

  • In vitro, MNTX dose-dependently reduced morphine-induced inhibition of muscle contractions in naïve guinea pigs (IC50 = 9.4 x 10(-8)M).
  • In chronically treated guinea pigs, MNTX abolished morphine's inhibitory effect on muscle contractions.
  • In vivo, MNTX did not affect GI transit in naïve guinea pigs but reversed morphine-induced GI transit delay in chronically treated animals.

Conclusions:

  • MNTX effectively reverses opioid-induced inhibition of GI motility by acting on peripheral μOR.
  • MNTX demonstrates efficacy in both in vitro and in vivo models.
  • MNTX does not impact GI transit when opioid stimulation is absent, suggesting a targeted therapeutic action.

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