Distribution and types of adrenoceptors in the guinea-pig ileum: the action of alpha- and beta-adrenoceptor agonists
Abstract
1 Segments of guinea-pig ileum and the myenteric plexus-longitudinal smooth muscle preparation were used for a study of the actions of adrenaline, noradrenaline, isoprenaline, ephedrine and phenylephrine on the responses of coaxially stimulated ileum at different distances from the ileocaecal valve.2 The responses of the ileum to electrical stimulation were suppressed by adrenaline, nonadrenaline and ephedrine, while phenylephrine and isoprenaline inhibited them only partially.3 The twitch inhibition elicited by these adrenoceptor agonists was the same at all distances from the ileocaecal valve. There was no significant difference between their cumulative and non-cumulative concentration-response curves.4 Smooth muscle relaxation was induced only by isoprenaline and contraction only by phenylephrine at all distances from the ileocaecal junction. Adrenaline and noradrenaline evoked smooth muscle contraction in the terminal (0 to 20 cm), a concentration-dependent, biphasic response in the intermediate part (21 to 50 cm) and a relaxation in the proximal ileum (> 50 cm from the ilecocaecal valve). Ephedrine did not change significantly the smooth muscle tension in the terminal and the intermediate segments and induced smooth muscle...Continue Reading
References
Differentiation between pre- and postjunctional alpha-receptors in guinea pig ileum and rabbit aorta
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