EFFECT OF BEVERAGE OSMOLALITY ON INTESTINAL FLUID ABSORPTION DURING EXERCISE

To determine how osmolality of an orally ingested fluid-replacement be verage would alter intestinal fluid absorption from the duodenum and/o r jejunum during 85 min of cycle exercise (63.3 +/- 0.9% peak O-2 upta ke) in a cool environment (22 degrees C), seven subjects (5 men, 2 wom en, peak Oz uptake = 54.5 +/- 3.8 ml kg-l min-l) participated in four experiments separated by 1 wk in which they ingested a water placebo ( WP) or one of three 6% carbohydrate (CHO) beverages formulated to give mean osmolalities of 197, 295, or 414 mosmol/kgH(2)O. CHO solutions a lso contained 17-18 meg Na+ and 3.2 meg K+. Nasogastric and multilumen tubes were fluoroscopically positioned in the gastric antrum and duod enojejunum, respectively. Subjects ingested a total of 23 ml/kg body m ass of the test solution, 20% (370 +/- 9 mi) of this volume 5 min befo re exercise and 10% (185 +/- 4 mi) every 10 min thereafter. By using t he rate of gastric emptying as the rate of intestinal perfusion (G. P. Lambert, R. T. Chang, D. Joensen, X. Shi, R. W. Summers, H. P. Schedl , and C. V. Gisolfi. Int. J. Sports Med. 17: 48-55, 1996), intestinal absorption was determined by segmental perfusion from the duodenum (0- 25 cm) and jejunum (25-50 cm). There were no differences (P > 0.05) in gastric emptying (mean 18.1 +/- 1.3 ml/min) or total fluid absorption (802 +/- 109, 650 +/- 52, 674 +/- 62, and 633 +/- 74 ml.50 cm(-1).h(- 1) for WP, hypo-, iso-, and hypertonic solutions, respectively) among beverages; but WP was absorbed faster (P < 0.05) from the duodenum tha n in the jejunum. Of the total volume of fluid ingested, 82 +/- 14, 74 +/- 6, 76 +/- 5, and 68 +/- 7% were absorbed for WP,hypo-, iso-, and hypertonic beverages, respectively. There were no differences in urine production or percent change in plasma volume among solutions. We con clude that total fluid absorption of 6% CHO-electrolyte beverages from the duodenojejunum during exercise, within the osmotic range studied, is not different from WP.