Effects of cycle exercise on intestinal absorption in humans

Abstract

Intestinal absorption was measured in six trained male cyclists during rest, exercise, and recovery periods with the segmental perfusion technique. Each subject passed a multilumen tube into the duodenojejunum. The experiments consisted of 1) a sequence of 1-h bouts of cycling exercise at 30, 50, and 70% maximal O2 uptake (Vo2max) separated by 1-h rest periods or 2) a 90-min bout at 70% VO2max. The cycling was performed on a constant-load Velodyne trainer. Absorption of water and a 6% carbohydrate-electrolyte (2% glucose, 6% sucrose, 20 meq Na+, 2.6 meq K+) solution (both perfused at 15 ml/min) were compared. The effects of perfusing an isotonic electrolyte solution during mild (30% VO2max) exercise were also studied. Fluid was sampled every 10 min from ports 10 and 50 cm distal to the infusion site. Water flux was determined by differences in polyethylene glycol concentration across the 40-cm test segment. Results showed 1) no difference in water or electrolyte absorption rates among rest, exercise, and recovery periods; 2) no difference in absorption rates among the three exercise intensities or different exercise durations; and 3) significantly greater fluid absorption rates from the carbohydrate-electrolyte (CE) solution than from water. Water flux during rest, exercise, and recovery was about sixfold greater from the CE solution than from the isotonic solution without carbohydrate. We conclude that 1) exercise has no effect on water or solute absorption in the duodenojejunum, 2) fluid absorption occurs significantly faster from a CE solution than from water, and 3) fluid absorption is increased sixfold by addition of carbohydrate to an electrolyte solution.

Water and Solute Absorption From Carbohydrate-Electrolyte Solutions in the Human Proximal Small Intestine: A Review and Statistical Analysis

“…This is not in agreement with two 3-O-methyl-D-glucose recovery studies (Lang, Gisolfi, & Lambert, 2006;Van Nieuwenhoven, Brouns, & Brummer, 1999) suggesting a decrease of CHO absorption during exercise at 70%VO 2max and is not consistent with the evidence available from the intestinal-perfusion studies that reported no effect on CHO absorption in the duodenojejunum (Gisolfi et al, 1991) and in the jejunum (Fordtran & Saltin, 1967) during exercise at 64-78% VO 2max . What could possibly cause an increase of CHO absorption in the jejunum during exercise when the available data from different laboratories are combined?…”

“…An early study from Fordtran and Saltin (1967) reported no consistent effect of exercise on glucose, fluid, or electrolyte absorption during treadmill running for 1 hr at 64-78% VO 2max . Gisolfi et al (1991) studied intestinal absorption of fluid and CHO during 1-hr bouts of cycle exercise at 30%, 50%, and 70% VO 2max and also found no exercise effect on absorption. However, Barclay and Turnberg (1988) found that water and electrolyte absorption in the jejunum were reduced during 50 min of moderate-intensity (mean heart rate 107 ± 7 beats/min) cycle exercise at 15 km/hr even though the values for water and solute absorption were extremely low.…”

“…There were three studies of intestinal perfusion during exercise reporting total solute absorption data, but they provided no comparison with at-rest conditions Rogers et al, 2005;Ryan, Bleiler, Carter, & Gisolfi, 1989). There were also three intestinal-perfusion studies comparing water absorption during exercise and at rest but not reporting total solute absorption (Barclay & Turnberg, 1988;Fordtran & Saltin, 1967;Gisolfi et al, 1991). Therefore, the finding that exercise produced a significantly greater total solute absorption rate than that at rest in the jejunum and not in the duodenojejunum (Table 4) is worthy of further investigation.…”

The Hyponatremia of Exercise

“…Rather, it must be due to reduced rates of intestinal absorption of glucose and, by inference, also of water. Indeed the study of Gisolfi et al (25) found that only 37% of fluid perfused into the duodenum and jejunum at rates of 900 ml/hr was absorbed.…”

“…and that these losses can be considerable especially if the ingested solution has a high (>lo%) carbohydrate content (25,26,82). Furthermore, since most subjects who develop the hyponatremia of exercise do not vomit excessively, hyponatremia can clearly develop even if the translocated sodium is not lost in vomitus.…”