Effects of medetomidine on intestinal and colonic motility in the dog.
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.
Maugeri
S
S
Laboratory of Pharmacology, Faculty of Veterinary Medicine, University of Pisa, Italy.
Ferrè
J P
JP
Intorre
L
L
Soldani
G
G
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D003106:Colon / Q000187:drug effects* / Q000502:physiology; D004285:Dogs / Q000502:physiology*; D004347:Drug Interactions; D004594:Electrophysiology; D005769:Gastrointestinal Motility / Q000187:drug effects*; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology*; D007275:Injections, Intravenous / Q000662:veterinary; D007583:Jejunum / Q000187:drug effects* / Q000502:physiology; D020926:Medetomidine; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000700:Analgesics; D006993:Hypnotics and Sedatives; D007093:Imidazoles; C050701:atipamezole; D015016:Yohimbine; D003000:Clonidine; D020926:Medetomidine