Inhibition of the cholinergic twitch response in guinea-pig common bile duct: an evaluation of the effects of noradrenaline, clonidine and fentanyl.
Presynaptic inhibitory effects of noradrenaline, clonidine and fentanyl on twitch contractions evoked by transmural electrical stimulation were investigated in guinea-pig common bile duct (CBD). Antagonism of the response to fentanyl by naloxone and to noradrenaline and clonidine by yohimbine confirmed the involvement of presynaptic opiate and alpha 2-adrenoceptors respectively. Clonidine caused desensitization of presynaptic alpha 2-adrenoceptors. No cross desensitization between clonidine and fentanyl was observed. Furthermore, partial agonistic activity of clonidine at presynaptic alpha 2-adrenoceptors was also observed by the antagonism of noradrenaline response in this preparation.
Sahin-Erdemli
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Department of Pharmacology, Faculty of Pharmacy, Hacettepe University, Ankara, Turkey.
Uma
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D000109:Acetylcholine / Q000502:physiology*; D000818:Animals; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004558:Electric Stimulation; D005283:Fentanyl / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006168:Guinea Pigs; D006500:Hepatic Duct, Common / Q000187:drug effects*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
D015016:Yohimbine; D009270:Naloxone; D003000:Clonidine; D000109:Acetylcholine; D005283:Fentanyl; D009638:Norepinephrine