Effect of hypohydration on gastric emptying and intestinal absorption during exercise

Dehydration and hyperthermia may impair gastricemptying (GE) during exercise; the effect of these alterations onintestinal water flux (WF) is unknown. Thus the purpose of this studywas 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 alsocompare 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 andvia a multilumen tube that spanned the duodenum and the first 25 cm ofjejunum. Hypohydration was attained 12-16 h before experiments bylow-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 · kg¹ · min¹)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 (~2.0liters total) were ingested as a large bolus (4.6 ml/kg body wt) 5 minbefore exercise and as small serial feedings (2.3 ml/kg body wt) every10 min of exercise. Average GE rates were not different amongconditions (P > 0.05). Mean(±SE) values for WF were also similar(P > 0.05) for the euhydration (15.3 ± 1.7 ml · cm¹ · h¹)and hypohydration (18.3 ± 2.6 ml · cm¹ · h¹)experiments. During exercise after hypohydration, waterabsorption 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°C),heart rate (152 ± 1 beats/min), and change in plasma volume(5.7 ± 0.7%) were similar among experimental trials. Weconclude that 1) hypohydration to~3% body weight does not impair GE or fluid absorption duringmoderate exercise when ingesting WP, and2) hyperosmolality (>400 mosmol)reduced WF in the proximal intestine.