title: Presynaptic alpha-adrenoceptor mediated inhibition of the neurogenic cholinergic contraction in the isolated intestinal bulb of the carp (Cyprinus carpio).
abstract: The effects of norepinephrine, epinephrine and clonidine on neurogenic cholinergic contraction were examined in the presence of a beta-adrenoceptor blocking agent, carteolol (5 X 10(-6) M), in the isolated intestinal bulb of the carp. Norepinephrine, epinephrine (10(-9)-10(-6) M) and clonidine (10(-8)-10(-5) M) inhibited the contraction induced by low frequency (2 or 5 Hz) transmural stimulation (TMS) without inhibiting the contraction induced by acetylcholine (ACh, 6 X 10(-8)-4 X 10(-7) M). Methoxamine (10(-4) M) and phenylephrine (10(-4) M) showed no such inhibitory effect on the TMS-induced contraction. The inhibitory effects of catecholamines and clonidine were decreased by phentolamine (5.4 X 10(-6) M) and yohimbine (10(-7)-10(-6) M) but not by prazosin (7 X 10(-7)-10(-6) M). Nicotine (10(-6)-10(-4) M) and serotonin (3 X 10(-8)-3 X 10(-6) M) caused contraction of the intestinal bulb indirectly by releasing endogenous ACh. This contraction was inhibited by norepinephrine, epinephrine and clonidine in a concentration-dependent manner. The present results suggest that catecholamines and clonidine inhibit cholinergic transmission via the activation of a presynaptic alpha-adrenoceptor (presumably of alpha-2 type) located on the cholinergic nerve terminals innervating the smooth muscle of the intestinal bulb of the carp.
authors.forename: T
authors.initials: T
authors.lastname: Kitazawa
authors.forename: K
authors.initials: K
authors.lastname: Temma
authors.forename: H
authors.initials: H
authors.lastname: Kondo
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002347:Carps / Q000502:physiology*; D002395:Catecholamines / Q000378:metabolism; D003000:Clonidine / Q000494:pharmacology; D003530:Cyprinidae / Q000502:physiology*; D004558:Electric Stimulation; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009538:Nicotine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D002395:Catecholamines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D013779:Tetrodotoxin; D009538:Nicotine; D001285:Atropine; D008729:Methoxamine; D003000:Clonidine; D009638:Norepinephrine; D011224:Prazosin; D004837:Epinephrine; D010646:Phentolamine