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Effects of medetomidine on intestinal and colonic motility in the dog
S Maugeri1, J P Ferrè, L Intorre
1Laboratory of Pharmacology, Faculty of Veterinary Medicine, University of Pisa, Italy.
Abstract:
The motor responses of the jejunum and colon to stimulation of alpha 2-adrenoceptors by medetomidine and clonidine were investigated in four dogs. In fasting dogs, medetomidine, at a dose rate of 30 micrograms/kg i.v., disrupted the migrating myoelectric complex (MMC) pattern of the small intestine for about 2 h. Similar, but shorter-lasting effects were also induced by clonidine (30 micrograms/kg i.v.) on the jejunum. The administration of alpha 2-agonists inhibited colonic motility in fasting dogs, although medetomidine-induced inhibition was preceded by a short period of increased muscle tone. All these effects were reversed by the alpha 2-antagonists atipamezole (0.15 mg/kg i.v.) and yohimbine (0.20 mg/kg i.v.). In fed dogs, medetomidine (30 micrograms/kg i.v.) induced a strong increase of the tone on the proximal colon, while the activity of the medium and distal colon was completely suppressed. Yohimbine (0.50 mg/kg i.v.) immediately restored the activity of the colon and induced a propagated giant contraction and defaecation by the animal. These data confirm the importance of alpha 2-adrenergic receptors in the control of intestinal and colonic motility in the dog.
Insights
Alpha 2-adrenergic agonists like medetomidine disrupt canine intestinal motility and inhibit colonic function. Antagonists reversed these effects, confirming alpha 2-receptors
Area of Science:
- Pharmacology
- Gastroenterology
- Veterinary Medicine
Background:
- Alpha 2-adrenoceptors play a role in regulating gastrointestinal motility.
- Understanding their function is crucial for managing digestive disorders.
Purpose of the Study:
- To investigate the effects of alpha 2-adrenoceptor agonists (medetomidine, clonidine) on jejunal and colonic motility in dogs.
- To determine the role of alpha 2-adrenergic receptors in controlling canine intestinal and colonic motor responses.
Main Methods:
- Administered medetomidine and clonidine intravenously to fasting and fed dogs.
- Observed effects on the migrating myoelectric complex (MMC) and colonic motility.
- Utilized alpha 2-antagonists (atipamezole, yohimbine) to reverse agonist-induced effects.
Main Results:
- Medetomidine and clonidine disrupted the small intestinal MMC pattern in fasting dogs.
- Alpha 2-agonists inhibited colonic motility, with medetomidine causing initial increased tone.
- In fed dogs, medetomidine increased proximal colonic tone and suppressed distal activity; yohimbine reversed this, inducing contractions and defecation.
Conclusions:
- Alpha 2-adrenergic receptors significantly influence jejunal and colonic motility in dogs.
- Agonist-induced motor patterns can be modulated by receptor antagonism.
- These findings highlight the therapeutic potential of targeting alpha 2-adrenoceptors in canine gastrointestinal conditions.