Regulation of salt and water absorption by the canine ileum during head upward tilting



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Head upward tilting causes a compensatory reduction in blood flow to the gut . The purpose of this investigation was to determine if head upward tilting could alter the rate .of intestinal absorption of salt, water, and sugar by virtue of reflex action on the cardiovascular system and also to determine which aspect of intestinal transport is primarily affected. Mongrel dogs of both sexes were used in this study. Uni-directional fluxes of [raised 22]Na, [raised 3]H[lowered 2]O, and 3-0-[raised 14]CH[lowered 3]-D-glucose were measured from a ten inch segment of terminal ileum which had been isolated with its nerve and blood supply intact. Despite reduced blood flow to the gut, net salt and water absorption increased. A decrease in the absorption of 3-0-methyl-glucose was noted. Increased transmural potential, with the mucosa becoming more positive, was observed during the head upward tilting period. The changes in net flux of Na were due to the combined effects of changes in the influx and outflux of Na, neither one by itself being significantly altered. The increased net absorption of water was due to an increased difference between the influx and outflux of water, both of which decreased significantly. Reduction of the sugar absorption could be accounted for by the decreased blood supply to the segment. This reduction in blood supply can decrease transport by failing to supply sufficient oxygen and nutrients to maintain a normal level of activity for all transport processes. Increased transmural potential could be accounted for by the decrease in NaCl concentration in the intestinal lumen.