[Enhancement of the contraction of the isolated duodenum and Oddi's sphincter of rabbits by alpha adrenergic agents].
Effects of some alpha- and beta-adrenoceptor agonists were investigated on the isolated rabbit sphincter of Oddi and duodenum. In both preparations, noradrenaline (10(-6)-10(-5) M) inhibited the rhythmic spontaneous contractions, and the inhibition was observed more markedly in the sphincter than in the duodenum. In the duodenum, phenylephrine (10(-6)-10(-5) M) induced an inhibition of the contractions of rapid onset followed by an increase in contraction height. The response resembled that by noradrenaline in the presence of propranolol 10(-6) M. 10(-5) M of phenylephrine introduced the increase in contractions more remarkably than 10(-6) M of the drug. Isoproterenol (10(-7)-10(-6) M), as well as noradrenaline in the presence of phentolamine 10(-5) M, produced an inhibition of slow onset which was maintained throughout the presence of the drug. The inhibition by noradrenaline with phentolamine was more intense than that without phentolamine. Qualitatively similar responses to phenylephrine and isoproterenol were observed on the sphincter of Oddi. In both preparations, tetrodotoxin at 10(-7) M potentiated the inhibition induced by noradrenaline, depressed the increase in contractions by phenylephrine, but hardly affected the response to isoproterenol. The results indicate that, in the sphincter of Oddi and duodenum in rabbits, adrenergic agonists produce inhibition of the contractions via alpha- and beta-receptors in the smooth muscle fibres, and abrupt inhibition by alpha-agonist may cause excitatory response mediated through neural consequence.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D004386:Duodenum / Q000187:drug effects; D005260:Female; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011817:Rabbits; D009803:Sphincter of Oddi / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D010656:Phenylephrine; D007545:Isoproterenol; D009638:Norepinephrine