EFFECT OF HYPOHYDRATION ON GASTRIC-EMPTYING AND INTESTINAL-ABSORPTIONDURING EXERCISE

Dehydration and hyperthermia may Impair gastric emptying (GE) during e xercise; the effect of these alterations on intestinal water flux (WF) is unknown. Thus the purpose of this study was to determine the effec t of hypohydration (similar to 2.7% body weight) on GE and WF of a wat er placebo (WP) during cycling exercise (85 min, 65% maximal oxygen up take) in a cool environment (22 degrees C) and to also compare GE and WF of three carbohydrate-electrolyte solutions (CES) while the subject s were hypohydrated. GE and WF were determined simultaneously by a nas ogastric tube placed in the gastric antrum and via a multilumen tube t hat spanned the duodenum and the first 25 cm of jejunum. Hypohydration was attained 12-16 h before experiments by low-intensity exercise in a hot (45 degrees C), humid (relative humidity 50%) environment. Seven healthy subjects (age 26.7 +/- 1.7 yr, maximal oxygen uptake 55.9 +/- 8.2 ml.kg(-1).min(-1)) ingested either WP or a 6% (330 mosmol), 8% (4 00 mosmol), or a 9% (590 mosmol) CES the morning following hypohydrati on. For comparison, subjects ingested WP after a euhydration protocol. Solutions (similar to 2.0 liters total) were ingested as a large bolu s (4.6 ml/kg body wt) 5 min before exercise and as small serial feedin gs (2.3 ml/kg body wt) every 10 min of exercise. Average GE rates were not different among conditions (P > 0.05). Mean (+/-SE) values for WF were also similar (P > 0.05) for the euhydration (15.3 +/- 1.7 ml cm- l h-l) and hypohydration (18.3 +/- 2.6 ml.cm(-1) h-l) experiments. Dur ing exercise after hypohydration, water absorption was greater (P < 0. 05) with ingestion of WP (18.3 +/- 2.6) and the 6% CES (16.5 +/- 3.7), compared with the 8% CES (6.9 +/- 1.5) and the 9% CES (1.8 +/- 1.7). Mean values for final core temperature (38.6 +/- 0.1 degrees C), heart rate (152 +/- 1 beats/min), and change in plasma volume (-5.7 +/- 0.7 %) were similar among experimental trials. We conclude that I) hypohyd ration to similar to 3% body weight does not impair GE or fluid absorp tion during moderate exercise when ingesting WP, and 2) hyperosmolalit y (>400 mosmol) reduced WF in the proximal intestine.