Digestive Diseases and Sciences, Vol. 40, No. 4 (April 1995), pp. 774-780 Na+/H + Exchange Mediates Postprandial Ileal Water and Electrolyte Transport OSCAR J. HINES, MD, ANTON J. BILCHIK, MD, PhD, DAVID W. MCFADDEN, MD, PAULA J. RODGERS, MD, NORMAN BAUTISTA, MD, MICHAEL J. ZINNER, MD, and STANLEY W. ASHLEY, MD Feeding stimulates fluid and electrolyte absorption in the small intestine. Previous studies have suggested that Na+/gtucose cotransport is important in initiating this response in the jejunum. The purpose of this study was to determine whether Na+/H + exchange plays a role in meal-induced absorption. Exteriorized, neurovascularly intact jejunal and ileal loops (25 cm) were constructed in dogs. Following a two-week period of postoperative recovery, the loops of awake dogs were perfused with standard buffer alone or with increasing concentra- tions of amiloride, a Na+/H + exchange inhibitor. Water, sodium, and chloride fluxes were 14, calculated following a meal using [ C]PEG as a volume marker. The meal significantly increased absorption in both the jejunum (P < 0.001) 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 response in the ileum was dose dependent. These findings suggest that a major mediator of postprandial sodium and water absorption in the ileum is the Na+/H + exchanger. KEY WORDS: Na+/H + exchange; proabsorption; small intestine; amiloride. The regulation of intestinal absorption has been the focus of considerable experimental effort. Although these studies have yielded new information, most have been performed using in vitro preparations and have focused on the mechanisms of transport in the fasting state (1). The few studies examining in vivo transport have examined primarily the neural and hormonal control of intestinal absorption (2-7). In contrast, the cellular mechanisms responsible for the Manuscript received December 26, 1993; revised manuscript received November 4, 1994; accepted November 8, 1994. From the Department of Surgery, UCLA Medical Center and Sepulveda VA Medical Center, Los Angeles, California. Supported by NIH R29-DK-47326 (S.W.A.), R01-DK-39879 (M.J.Z.), and a VA Merit Review (D.W.M.). Portions of this work were presented at the Annual Meeting of the American Gastroenterological Association, May 1993, Boston, Massachusetts. Address for reprint requests: Dr. Stanley W. Ashley, Department of Surgery, Division of General Surgery, 10833 Le Conte Avenue (72-215 CHS), Los Angeles, California 90024. increase in absorption of fluid and electrolytes follow- ing a meal have received little attention. We have investigated the role of Na+/glucose co- transport in the postprandial proabsorptive response of canine jejunal Thiry-Vella loops (8). This study suggested that the increase in absorption following a meal is due, at least in part, to activation of the cotransporter. The increase appears to be character- ized by short-term adaptation of the enterocyte and a translational increase in transporter synthesis (9). The majority of sodium transport in the small in- testine occurs by two cellular mechanisms (1). In addition to Na+/substrate cotransport, Na+/H + ex- change has been clearly demonstrated (10). Evidence of the presence of the Na+/H + antiporter has been verified in both the jejunum (11, 12) and ileum (13, 14). Between meals the majority of intestinal NaCI absorption involves electrogenically neutral apical Na+/I-I + and CI-/HCO 3- exchange (14, 15). The aim of this study was to investigate the role of 774 Digestive Diseases and Sciences, Vol. 40, No. 4 (April 1995) 0163-2116195/0400-u774507.50/0 © 1995 Plenum Publishing Corporation