Effect of dehydration on gastrointestinal function at rest and during exercise in humans

Dehydration leads to the aggravation of gastrointestinal (GI) complaints du ring exercise. The aim of this study was to examine the effect of dehydrati on on various GI parameters during strenuous exercise. Ten healthy well-tra ined men were investigated in dehydrated and in euhydrated conditions. Dehy dration took place before the experiments using a dehydration regimen in a sauna leading to a 3% loss of body mass. Each experiment consisted of 1 h p re-exercise rest, 1.5 h cycling at 70% maximal exercise intensity, and 3.5 h post-exercise rest. During cycling, liquid gastric emptying (GE), orocaec al transit time (OCTT) and intestinal permeability and glucose absorption w ere measured. The GI-symptoms were scored using a questionnaire. Body tempe rature, plasma volume and vasopressin were measured before and after cyclin g. The GE was significantly slower during dehydration [median time to peak C-13 enrichment in the breath sample (C-13-TTP) 23.6 min, range 13.7-50.0 m in, P = 0.02] than in the control situation (median C-13-TTP 17.1 min, rang e 9.8-38.4 min). The OCTT was unchanged (median 173 min, range 98-263 min c ompared to median 128 min, range 98-195 min, P = 0.18). Dehydration did not change intestinal permeability, glucose absorption, plasma volume, rectal temperature or plasma vasopressin concentration. In the dehydration experim ent, exercise induced a significant increase in nausea (P = 0.01) and epiga stric cramps (P = 0.05), in contrast to the control situation. In both expe riments, exercise led to a significant increase in rectal temperature and p lasma vasopressin concentration, and a significant decrease in plasma volum e. The increase in plasma vasopressin concentration was significantly highe r in the dehydration experiment (P = 0.015). No significant differences in either the post-exercise rectal temperatures or in plasma volumes was obser ved. The difference in GE between the two experiments was significantly cor related with the difference in nausea score (I = 0.87, P = 0.002). We concl uded that dehydration leads to a delayed GE but not to differences in OCTT, intestinal permeability or glucose uptake during intense cycling. The dela y in GE is significantly associated with an increase in exercise-induced na usea.