INTESTINAL-ABSORPTION DURING REST AND EXERCISE - IMPLICATIONS FOR FORMULATING AN ORAL REHYDRATION SOLUTION (ORS)

Formulation of oral rehydration solutions (ORS) is reviewed in the con text of methods for measuring absorption of water and component substr ates, transport mechanisms of substrates and water, requirements of th e athlete, and effects of exercise on absorption. The triple lumen tub e intubation perfusion method is the optimal technique for obtaining a bsorption data from the human small intestine during rest and exercise . Factors that must be considered when interpreting absorption data ob tained by this technique include the role of the mixing segment in alt ering composition of the infused solution, defining optimal segment le ngth, effects of ORS osmolality, arid absorption of ''nonabsorbed'' in dicators. Absorption data are applicable only to the test segment and may lack relevance to ORS transport proximal and distal to the test se gment. Absorption rate of an ORS measured by perfusion may not correla te with absorption rate following ingestion. Transport of water, elect rolytes, carbohydrates, and other solutes including glutamine and amin o acids is considered in relation to ORS formulation. Factors affectin g absorption of an ORS including the unstirred layer, motility, intest inal blood flow, and maximal absorptive capacity pf the alimentary tra ct are considered. Exercise per se at 30-70% VO2max far 60-90 min prob ably has minimal effects in limiting absorption of an ORS. Considerati on relevant to supplying needs of the athlete during prolonged exercis e in relation for ORS formulation are discussed.