Antagonistic effects of alpha-adrenoceptor blocking agents on reticuloruminal hypomotility induced by xylazine in cattle.
The intravenous injection of a standard dose (0.05 mg/kg) of xylazine inhibited reticuloruminal motility in cattle. Pretreatment with adrenoceptor antagonists showing alpha 2-blocking activity, tolazoline (0.5 mg/kg) and yohimbine (0.2 mg/kg), antagonized the xylazine-induced reticuloruminal amotility. Tolazoline was more effective than yohimbine, since an antagonistic effect was not seen at 0.5 mg/kg yohimbine, and yohimbine at 0.2 mg/kg was less effective than tolazoline at 0.5 mg/kg. An adrenoceptor antagonist showing alpha 1-blocking activity, prazosin, did not prevent the inhibition of reticuloruminal motility by xylazine. The xylazine-induced reticuloruminal amotility was also not prevented by either a dopamine receptor antagonist, domperidone, or an opiate receptor antagonist, naloxone. These results suggest that xylazine inhibits bovine reticuloruminal motility through its activation of alpha 2-adrenoceptors, and show that tolazoline can be used as a specific antagonist of xylazine in studies of the alpha-adrenergic influence on reticuloruminal motility in cattle.
Hikasa
Y
Y
Department of Veterinary Surgery, School of Veterinary Medicine and Animal Sciences, Kitasato University, Aomori, Japan.
Takase
K
K
Emi
S
S
Ogasawara
S
S
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004294:Domperidone / Q000494:pharmacology; D005260:Female; D005769:Gastrointestinal Motility / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D012159:Reticulum / Q000187:drug effects; D012417:Rumen / Q000187:drug effects; D013843:Thiazines / Q000494:pharmacology*; D014043:Tolazoline / Q000494:pharmacology; D014991:Xylazine / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D013843:Thiazines; D014991:Xylazine; D015016:Yohimbine; D009270:Naloxone; D004294:Domperidone; D014043:Tolazoline; D011224:Prazosin