Loperamide: evidence for a centrally mediated opioid effect on rumen motility in conscious goats and sheep.
Loperamide inhibited the frequency and amplitude of cyclical contractions of the rumen in conscious goats (100 micrograms/kg, i.v. and sheep (250 micrograms/kg, i.v.). In goats, the inhibitory effect of loperamide could be prevented by pretreatment with the opiate antagonist naltrexone (greater than or equal to 12.5 micrograms/kg, i.v.) but not by pretreatment with the dopaminergic antagonist domperidone (500 micrograms/kg, i.v.). Intracerebroventricular administration of 1 microgram/kg loperamide in goats significantly depressed ruminal contraction frequency, whereas intravenous administration of 10 micrograms/kg loperamide did not affect cyclical motility. Administered via the carotid artery, loperamide (4 micrograms/kg) depressed both frequency and amplitude of cyclical contractions of reticulum and rumen, whereas the same dose was ineffective via the coeliac artery. In vitro, loperamide (10 nM-100 microM) had no influence on spontaneous activity or tone of the reticular longitudinal muscle strips. It is concluded that loperamide inhibits cyclical ruminal contractions through a central opioid pathway.
Maas
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van Duin
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van Miert
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D000818:Animals; D004294:Domperidone / Q000494:pharmacology; D005769:Gastrointestinal Motility / Q000187:drug effects*; D006041:Goats / Q000502:physiology*; D007700:Kinetics; D008139:Loperamide / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology; D009294:Narcotics; D010880:Piperidines / Q000494:pharmacology*; D012417:Rumen / Q000187:drug effects / Q000502:physiology*; D012756:Sheep / Q000502:physiology*
D009294:Narcotics; D010880:Piperidines; D004294:Domperidone; D009271:Naltrexone; D008139:Loperamide