Studies of the mechanism of noradrenaline stimulation of fluid absorption by rat jejunum in vitro.

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Abstract
The everted-sac technique was used to study the mechanism of action of noradrenaline (norepinephrine) on fluid absorption by rat jejunum. Noradrenaline (10-3 M) significantly stimulated fluid absorption and this effect was dependent on the presence of Ca ions in the serosal fluid. Sr, but not Mg, could substitute for Ca. Verapamil, Mn and neodymium, all inhibitors of Ca transport, blocked noradrenaline-stimulated fluid absorption when present in the serosal compartment without any effect on basal or glucose-stimulated absorption. Inhibitors of the translation stage of protein synthesis inhibited the response whereas blocking the transcription stage of protein synthesis was without effect. The noradrenaline response was not attenuated by tetrodotoxin, suggesting that the response is not indirect due to noradrenaline altering endogenous intestinal nervous activity. Noradrenaline acts by opening Ca channels in the basolateral membranes of epithelial cells, resulting in an influx of Ca which stimulates ribosomal protein synthesis to produce proteins involved in fluid transport.