title: Antagonism by clonidine of the adenosine-induced inhibition of the twitch contraction of the guinea-pig Oddi sphincter.
abstract: The effects of clonidine on the purinergic inhibition of cholinergic transmission were investigated; we used the twitch contraction of a circular segment of the guinea-pig Oddi sphincter stimulated electrically. A circular segment of Oddi sphincter was contracted in a frequency-dependent manner by transmural nerve stimulation. Adenosine (10(-6) to 10(-4] produced a reduction of approximately 40% in the twitch contraction elicited at 5 Hz. The inhibition was antagonized by theophylline (10(-5) M), 8-phenyltheophylline (10(-6) M) or clonidine (10(-6) to 3 X 10(-6) M) but was enhanced by dipyridamole (3 X 10(-6) M). This antagonism produced by clonidine (3 X 10(-6) M) was almost unaffected by yohimbine (3 X 10(-6) M). The twitch contraction was also suppressed by N6-substituted adenosine analogs, L-PIA and CHA. The suppression was counteracted by theophylline or clonidine. The contraction produced by exogenously administered acetylcholine was not affected by clonidine and/or adenosine at all. The results suggest that clonidine, like theophylline, seems to exert these antagonistic effects by acting on the neuronal adenosine receptors in the guinea-pig Oddi sphincter muscle.
authors.forename: T
authors.initials: T
authors.lastname: Katsuragi
authors.forename: T
authors.initials: T
authors.lastname: Inoue
authors.forename: T
authors.initials: T
authors.lastname: Furukawa
mesh_terms: D000241:Adenosine / Q000037:antagonists & inhibitors*; D000527:Alprostadil; D014670:Ampulla of Vater / Q000187:drug effects*; D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D004176:Dipyridamole / Q000494:pharmacology; D004558:Electric Stimulation; D006168:Guinea Pigs; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D011458:Prostaglandins E / Q000494:pharmacology; D012110:Reserpine / Q000494:pharmacology; D009803:Sphincter of Oddi / Q000187:drug effects*; D013806:Theophylline / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D006584:Hexamethonium Compounds; D011458:Prostaglandins E; D010660:Phenylisopropyladenosine; D015016:Yohimbine; D018738:Hexamethonium; D004176:Dipyridamole; D012110:Reserpine; D013806:Theophylline; D000527:Alprostadil; D000241:Adenosine; D003000:Clonidine