ABSORPTION FROM DIFFERENT INTESTINAL SEGMENTS DURING EXERCISE

This study evaluated intestinal absorption from the first 75 cm of the proximal small intestine during 85 min of cycle exercise [63.6 +/- 0. 7% peak O-2 consumption (VO2peak)] while subjects ingested either an i sotonic carbohydrate-electrolyte beverage (CHO-E) or a water placebo ( WP). The CHO-E beverage contained 117 mM (4%) sucrose, 111 mM (2%) glu cose, 18 meg Na+, and 3 meg K+. The two experiments were performed a w eek apart by seven subjects (6 men and 1 woman; mean VO2peak = 53.5 +/ - 6.5 ml.kg(-1).min(-1)). Nasogastric and multilumen tubes were fluoro scopically positioned in the gastric antrum and duodenojejunum, respec tively. Subjects ingested 23 ml/kg body weight of the test solution, 2 0% (383 +/- 11 ml) of this volume 5 min before exercise and 10% (191 /- 5 ml) every 10 min thereafter. By using the rate of gastric emptyin g (18.1 +/- 1.1 vs. 19.2 +/- 0.7 ml/min for WP and CHO-E, respectively ) as the rate of intestinal perfusion, intestinal absorption was deter mined by segmental perfusion from the duodenum (0-25 cm) and jejunum ( 25-50 and 50-75 cm). Water flux was different (P < 0.05) between solut ions in the 0- to 25- and 25- to 50-cm segments for WP vs. CHO-E (30.7 +/- 2.7 vs. 15.0 +/- 2.9 and 3.8 +/- 1.1 vs. 11.9 +/- 3.3 ml.cm(-1).h (-1), respectively). Furthermore, water flux differed (P < 0.05) for W P in a comparison of the 0- to 25- to the 25- to 50-cm segment. Total solute flux (TSF) was not significantly different among segments for a given solution or between solutions for a given segment. There was no difference between trials for percent change in plasma volume. These results indicate that 1) fluid absorption in the proximal small intest ine depends on the segment studied and 2) solution composition can sig nificantly effect water absorption rate in different intestinal segmen ts.