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The everted-sac technique was used to study the mechanism of action of noradrenaline on fluid absorption by rat jejunum. Noradrenaline (10(-3) M) significantly stimulated fluid absorption and this effect was dependent on the presence of calcium ions in the serosal fluid. Strontium, but not magnesium could substitute for calcium. Verapamil, manganese and neodymium, all inhibitors of calcium 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. It is concluded that noradrenaline acts by opening calcium channels in the basolateral membranes of epithelial cells, resulting in an influx of calcium which stimulates ribosomal protein synthesis to produce proteins involved in fluid transport.
Parsons et al. (Mon,) studied this question.