SUMMARY Using a triple-lumen tube perfusion technique in normal human subjects secretin (2U/kg/hour intravenously) was shown to reduce the absorption of sodium, potassium, and chloride in the most proximal 30 cm of jejunum but it had no effect on bicarbonate absorption. This effect was not due to an artefact produced by the entry of secretin-stimulated, bicarbonate-rich, pancreatic juice into the test segment. Absorption of sodium chloride and water was stimulated rather than inhibited by higher bicarbonate concentrations and the effect of secretin was obvious even when this factor was controlled by adjusting the bicarbonate concentrations of the test fluids. Secretin did not influence ion transport in the mid-jejunum. It is suggested that the effects described may indicate a physiological role for secretin in the intestine where it could prevent the too rapid dehydration of upper jejunal contents which might interfere with adequate mixing and digestion.The effects of secretin on electrolyte secretion by the pancreas, biliary tree, and stomach are well recognized (Wormsley, 1968;Jonson, Sundman, and Thulin, 1964;Johnson and Grossman, 1971). There are, however, conflicting data on the effect of secretin on intestinal transport (Modigliani, Huet, Rambaud, and Bernier, 1971;Mekhjian, King, Sanzenbacher, and Zollinger, 1972;Moritz, Finkelstein, Meshkinpour, Fingerut, Siplet, and Lorber, 1972;Gardner, Peskin, Cerda, and Brooks, 1967;Barbezat and Grossman, 1971) and the present studies were performed to delineate more clearly its influence in the human jejunum and to assess the possibility that it is involved in the normal control of intestinal ion movement.
MethodsThirty-seven normal human adult volunteers who were fit undergraduate and postgraduate students aged 18 to 40 years were investigated using the triple-lumen tube perfusion technique of Ingelfinger (Cooper, Levitan, Fordtran, and Ingelfinger, 1966).This is an open-ended system which incorporates a 10 cm mixing segment to allow for endogenous secretions which enter the intestine from above. Test solutions were infused into the intestine at a constant rate and intestinal contents were conReceived for publication 13 March 1973. tinuously sampled, 10 cm and 40 cm distal to the point of infusion. Any changes in concentration which took place between the two aspiration sites must have occurred because of absorption or secretion within the segment of intestine lying between them. Since the proximal aspiration point always lay at least 20 cm distal to the ampulla of Vater, pancreatic and biliary secretion, although influencing the flow rate of fluid into the test segment of intestine, cannot be responsible for changes in concentration which occurred between the two aspiration sites. Any measured absorption or secretion thus occurs within the segment of intestine studied.Electrolyte and non-absorbable marker concentrations were measured in samples taken from the two aspiration sites.