Effect of hypohydration on gastric emptying and intestinal absorption during exercise

Departments of Exercise Science and Internal Medicine, University of Iowa, Iowa City, Iowa 52242 Dehydration and hyperthermia may impair gastric emptying (GE) during exercise; the effect of these alterations on intestinal water flux (WF) is unknown. Thus the purpose of this study was to determine the effect of hypohydration (~2.7% body weight) on GE and WF of a water placebo (WP) during cycling exercise (85 min, 65% maximal oxygen uptake) in a cool environment (22°C) and to also compare GE and WF of three carbohydrate-electrolyte solutions (CES) while the subjects were hypohydrated. GE and WF were determined simultaneously by a nasogastric tube placed in the gastric antrum and via a multilumen tube that 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°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% (400 mosmol), or a 9% (590 mosmol) CES the morning following hypohydration. For comparison, subjects ingested WP after a euhydration protocol. Solutions (~2.0 liters total) were ingested as a large bolus (4.6 ml/kg body wt) 5 min before exercise and as small serial feedings (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 1 · h 1 ) and hypohydration (18.3 ± 2.6 ml · cm 1 · h 1 ) experiments. During exercise after hypohydration, water absorption was greater ( P 400 mosmol) reduced WF in the proximal intestine. segmental perfusion; osmolality; plasma volume