NA+ H+ EXCHANGE MEDIATES POSTPRANDIAL ILEAL WATER AND ELECTROLYTE TRANSPORT/

Feeding stimulates fluid and electrolyte absorption in the small intes tine. Previous studies have suggested that Na+/glucose cotransport is important in initiating this response in the jejunum. The purpose of t his study was to determine whether Na+/H+ exchange plays a role in mea l-induced absorption. Exteriorized, neurovascularly intact jejunal and ileal loops (25 cm) were constructed in dogs. Following a two-week pe riod of postoperative recovery, the loops of awake dogs were perfused with standard buffer alone or with increasing concentrations of amilor ide, a Na+/H+ exchange inhibitor. Water, sodium, and chloride fluxes w ere calculated following a meal using [C-14]PEG as a volume marker. Th e meal significantly increased absorption in both the jejunum (P < 0.0 01) and ileum (P < 0.01) in those animals perfused with buffer alone. More significantly, amiloride suppressed the increased absorption seen following a meal in the ileum (P < 0.001) but not the jejunum. The re sponse in the ileum was dose dependent. These findings suggest that a major mediator of postprandial sodium and water absorption in the ileu m is the Na+/H+ exchanger.