Biomedical subjects

R T Chang

Publications and source records attributed to R T Chang.

9 recordsLinked to original sources

PubMed1998

Effect of hypohydration on gastric emptying and intestinal absorption during exercise.

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 ( approximately 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 degrees 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 degrees 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 ( approximately 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 < 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 degrees C), heart rate (152 +/- 1 beats/min), and change in plasma volume (-5.7 +/- 0.7%) were similar among experimental trials. We conclude that 1) hypohydration to approximately 3% body weight does not impair GE or fluid absorption during moderate exercise when ingesting WP, and 2) hyperosmolality (>400 mosmol) reduced WF in the proximal intestine.

Adult↗

PubMed1998

Effect of estrogen supplementation on exercise thermoregulation in premenopausal women.

This study examined the effects of 3 days of estrogen supplementation (ES) on thermoregulation during exercise in premenopausal (20-39 yr) adult women during the follicular phase of the menstrual cycle. Subjects (11 control, 10 experimental) performed upright cycle ergometer exercise at 60% of maximal O2 consumption in a neutral environment (25 degreesC, 30% relative humidity) for 20 min. Subjects were given placebo (P) or beta-estradiol (2 mg/tablet, 3 tablets/day for 3 days). All experiments were conducted between 6:30 and 9:00 AM after ingestion of the last tablet. Heart rate, forearm blood flow (FBF), mean skin temperature, esophageal temperature (Tes), and forearm sweat rate were measured. Blood analysis for estrogen and progesterone reflected the follicular phase of the menstrual cycle. Maximal O2 consumption (37.1 +/- 6.2 in P vs. 38.4 +/- 6.3 ml. kg-1. min-1 in ES) and body weight-to-surface area ratio (35.58 +/- 2.85 in P vs. 37.3 +/- 2.7 in ES) were similar between groups. Synthesis of 70-kDa heat shock protein was not induced by 3 days of ES. Neither the threshold for sweating (36.97 +/- 0.15 in P vs. 36.90 +/- 0.22 degreesC in ES), the threshold for an increase in FBF (37.09 +/- 0. 22 in P vs. 37.17 +/- 0.26 degreesC in ES), the slope of sweat rate-Tes relationship (0.42 +/- 0.16 in P vs. 0.41 +/- 0.17 in ES), nor the FBF-Tes relationship (10.04 +/- 4.4 in P vs. 9.61 +/- 3.46 in ES) was affected (P > 0.05) by 3 days of ES. We conclude that 3 days of ES by young adult women in the follicular phase of their menstrual cycle have no effect on heat transfer to the skin, heat dissipation by evaporative cooling, or leukocyte synthesis of 70-kDa heat shock protein.

Adult↗

PubMed1997

Fructose transport mechanisms in humans.

BACKGROUND & AIMS: The possible mechanisms of fructose transport are diffusion, a disaccharidase-related transport system, and glucose-facilitated fructose transport. However, these mechanisms in the human small intestine have not been systematically examined. This study was designed to investigate the mechanisms of fructose transport in the human duodenojejunum. METHODS: A triple-lumen tube was fluoroscopically positioned in the duodenojejunum of 7 men. Nine carbohydrate-electrolyte solutions were perfused at the rate of 15 mL/min. Acarbose and lactulose were used to examine the disaccharidase-related transport system and glucose-facilitated fructose transport, respectively. RESULTS: Fructose absorption was greater (P < 0.05) from fructose-glucose (FruGlu) and fructose-glucose-acarbose (FruGluA) solutions than from fructose-mannitol (FruMann) and fructose-mannitol-acarbose (FruMannA) solutions, but there was no difference between FruGlu and FruGluA solutions. A sucrose solution produced greater (P < 0.05) sucrose absorption than a sucrose-acarbose solution. Lactulose absorption (0.016-0.039 mmol.h-1.cm-1) was observed from solutions containing glucose or sucrose. Water absorption was not different among sucrose, FruGlu, and glucose solutions. FruMann solution produced net water secretion. These data suggest that free fructose and glucose transport were not inhibited by acarbose and that the presence of glucose induced lactulose absorption and enhanced fructose absorption. CONCLUSIONS: Fructose is transported transcellularly by facilitated diffusion and paracellularly (based on lactulose transport) via glucose-activated solution drag. In the human small intestine, free fructose and glucose transport does not occur via the disaccharidase system.

Acarbose↗

PubMed1997

Effect of running intensity on intestinal permeability.

Enhanced intestinal permeability has been associated with gastrointestinal disorders in long-distance runners. The primary purpose of this study was to evaluate the effect of running intensity on small intestinal permeability by using the lactulose and rhamnose differential urinary excretion test. Secondary purposes included assessing the relationship between small intestinal permeability and gastrointestinal symptoms and evaluating gastric damage by using sucrose as a probe. Six healthy volunteers [5 men, 1 woman; age = 30 +/- 2 yr; peak O2 uptake (VO2peak) = 57.7 +/- 2.1 ml.kg-1.min-1] rested or performed treadmill exercise at 40, 60, or 80% VO2peak for 60 min in a moderate environment (22 degrees C, 50% relative humidity). At 30 min into rest or exercise, the permeability test solution (5 g sucrose, 5 g lactulose, 2 g rhamnose in 50 ml water, approximately 800 mosM) was ingested. Urinary excretion rates (6 h) of the lactulose-to-rhamnose ratio were used to assess small intestinal permeability, and concentrations of each probe were determined by using high-performance liquid chromatography. Running at 80% VO2peak increased (P < 0.05) small intestinal permeability compared with rest, 40, and 60% VO2peak with mean values expressed as percent recovery of ingested dose of 0.107 +/- 0.021 (SE), 0.048 +/- 0.009, 0.056 +/- 0.005, and 0.064 +/- 0.010%, respectively. Increases in small intestinal permeability did not result in a higher prevalence of gastrointestinal symptoms, and urinary recovery of sucrose did not reflect increased gastric permeability. The significance and mechanisms involved in increased small intestinal permeability after high-intensity running merit further investigation.

Adult↗

PubMed1997

Absorption from different intestinal segments during exercise.

This study evaluated intestinal absorption from the first 75 cm of the proximal small intestine during 85 min of cycle exercise [63.6 +/- 0.7% peak O2 consumption (VO2 peak)] while subjects ingested either an isotonic carbohydrate-electrolyte beverage (CHO-E) or a water placebo (WP). The CHO-E beverage contained 117 mM (4%) sucrose, 111 mM (2%) glucose, 18 meq Na+, and 3 meq K+. The two experiments were performed a week apart by seven subjects (6 men and 1 woman; mean VO2 peak = 53.5 +/- 6.5 ml . kg-1 . min-1). Nasogastric and multilumen tubes were fluoroscopically positioned in the gastric antrum and duodenojejunum, respectively. Subjects ingested 23 ml/kg body weight of the test solution, 20% (383 +/- 11 ml) of this volume 5 min before exercise and 10% (191 +/- 5 ml) every 10 min thereafter. By using the rate of gastric emptying (18.1 +/- 1.1 vs. 19.2 +/- 0. 7 ml/min for WP and CHO-E, respectively) as the rate of intestinal perfusion, intestinal absorption was determined by segmental perfusion from the duodenum (0-25 cm) and jejunum (25-50 and 50-75 cm). Water flux was different (P < 0.05) between solutions in the 0- to 25- and 25- to 50-cm segments for WP vs. CHO-E (30.7 +/- 2.7 vs. 15.0 +/- 2.9 and 3.8 +/- 1.1 vs. 11.9 +/- 3.3 ml . cm-1 . h-1, respectively). Furthermore, water flux differed (P < 0.05) for WP in a comparison of the 0- to 25- to the 25- to 50-cm segment. Total solute flux (TSF) was not significantly different among segments for a given solution or between solutions for a given segment. There was no difference between trials for percent change in plasma volume. These results indicate that 1) fluid absorption in the proximal small intestine depends on the segment studied and 2) solution composition can significantly effect water absorption rate in different intestinal segments.

Adult↗

PubMed1996

Simultaneous determination of gastric emptying and intestinal absorption during cycle exercise in humans.

Because fluid absorption values derived from intestinal perfusion may not represent intestinal absorption of the same solution following its oral ingestion, the present study measured intestinal absorption following oral ingestion of a beverage. To do so required the simultaneous determination of gastric emptying. Seven males positioned a nasogastric tube in the gastric antrum and a multilumen tube in the duodenum under fluoroscopic guidance. Gastric emptying (GE) and intestinal water flux (WF) were measured during 85 min of cycle exercise at 60.6 +/- 3.7% VO2max (x +/- SE) in a 22 degrees C environment. Subjects ingested a total of 23 ml.kg-1 body weight (2005 +/- 187 ml) of a 6% isotonic carbohydrate-electrolyte solution by drinking 396 +/- 34 ml 5 min prior to exercise followed by 198 +/- 17 ml every 10 min during exercise. Mean stomach volume (312 +/- 80 ml) and GE (19.7 +/- 2.0 ml.min-1) did not change significantly after the initial 35 min equilibration period. Mean WF during oral ingestion of the solution (19.5 +/- 2.6 ml.cm-1.h-1) did not differ significantly from mean WF (16.4 +/- 1.9 ml.cm-1.h-1) during perfusion of the same solution directly into the duodenum at a rate equal to each subject's GE rate. Total solute flux (mmol.cm-1.h-1) was not different between drinking (4.1 +/- 1.3) and infusion (3.8 +/- 1.0) trials, nor were the changes in plasma volume. Urine production immediately following the exercise bout was unchanged between drinking (89.1 +/- 27.5 ml) and perfusion (88.5 +/- 24.2) experiments. These data indicate that: 1) relatively constant stomach volumes can be maintained over a prolonged period of time and can produce relatively constant GE rates, and 2) intestinal absorption of an isotonic carbohydrate-electrolyte beverage can be accurately determined by a modified segmental perfusion technique employing ingestion rather than intestinal perfusion.

Adult↗

PubMed1996

Gastrointestinal permeability following aspirin intake and prolonged running.

We sought to evaluate the effects of exercise and aspirin on gastroduodenal and intestinal permeability. Seven volunteers (age = 29 +/- 3 yr, VO2max = 56.8 +/- 4.1 ml.kg-1.min-1) rested or performed treadmill exercise (60 min at approximately 68% VO2max), with or without aspirin ingestion. Placebo (glucose) or aspirin (1.3 g) was taken the night before and prior to rest or exercise (total 2.6 g). A permeability test solution (approximately 1300 mOsm.kg-1), containing 10 g lactulose (L), 5 g mannitol (M), and 10 g sucrose (S), was ingested prior to rest or exercise. Urinary excretion rates (6.h-1), expressed as a percentage of ingested dose, were used to quantify intestinal (L/M ratio) or gastroduodenal (S) permeability. Ingestion of aspirin before running increased (P < 0.05) intestinal permeability compared to placebo+running and placebo+rest, but not compared to aspirin+rest; mean (+/-SE) values for the L/M ratio were 0.248 +/- 0.046, 0.029 +/- 0.012, 0.012 +/- 0.004, and 0.104 +/- 0.057, respectively. Gastroduodenal permeability following aspirin+running (3.25 +/- 1.21%) was also elevated (P < 0.05) compared to placebo+running (0.43 +/- 0.15%) and placebo+rest (0.24 +/- 0.11%), but not compared to aspirin+rest (0.66 +/- 0.27%). Neither running nor aspirin ingestion was associated with gastrointestinal (GI) complaints. Thus, GI permeability while running can be markedly elevated by aspirin ingestion.

Adult↗

PubMed1994

Effects of solution osmolality on absorption of select fluid replacement solutions in human duodenojejunum.

These experiments examined relationships between initial osmolality and carbohydrate (CHO) composition of an infused solution and osmolality and water and CHO absorption in a test segment. A triple-lumen tube with a 10-cm mixing segment and a 40-cm test segment was passed into the duodenojejunum. The infusion port was approximately 10 cm beyond the pyloric sphincter. Perfusion solutions were hypotonic (186 mosmol/kg; solution A), isotonic (283 mosmol/kg; solution B), and hypertonic (403 mosmol/kg; solution C). All solutions contained 18 meq Na+ and 3 meq K+. In the mixing segment, osmolality increased 83 mosmol/kg and decreased 90 mosmol/kg for solutions A and C, respectively. Corresponding changes in the test segment were an increase of 60 mosmol/kg and a decrease of 34 mosmol/kg. The osmolality of solution B did not change. In the test segment, mean osmolality and water and total solute fluxes were not significantly different among solutions, but solution C produced 27% greater fluid absorption than did solution A. When net fluid movement from mixing and test segments was determined, solution A produced 17% greater fluid absorption than did solution C. The mean increases in plasma and urine volumes over the 80-min test period were not significantly different. In the test segment, water flux correlated with CHO and Na+ fluxes but not with osmolality. In conclusion, 1) significant differences in solution osmolality were eliminated within the proximal duodenum and 2) perfusing 6% CHO solutions with osmolalities ranging from 186 to 403 mosmol/kg did not produce significant differences in fluid homeostasis (plasma volume) at the end of an 80-min test period.

Body Water↗

PubMed1993

Effects of carbonated and noncarbonated beverages at specific intervals during treadmill running in the heat.

Eight male runners performed four 2-hr treadmill runs at 65% VO2max in the heat (35 degrees C, 15-20% RH). A different beverage was offered each trial and subjects drank ad libitum for 2 min every 20 min. The beverages were, 6% carbohydrate (CHO) solution (NC 6), 6% carbonated-CHO solution (C 6), 10% CHO solution (NC 10), and 10% carbonated-CHO solution (C 10). NC 6 and C 6 contained 4% sucrose and 2% glucose. NC 10 and C 10 contained high fructose corn syrup. Subjects drank more NC 6 than C 6. Fluid consumption was not different among other trials. During all trials, volume consumed and % delta PV declined while heart rate and rectal temperature increased (p < 0.05). No significant differences occurred between beverages for these variables. Percent body weight lost was greater (p < 0.05) for the C 10 trial compared to the NC 6 trial. Neither sweat rate, percent fluid replaced, plasma [Na+], [K+], osmolality, percent of drink volume emptied from the stomach, or glucose concentration differed among trials. Plasma [K+] and osmolality increased (p < 0.05) over time. Ratings of fullness and thirst were not different among beverages, although both perceptions increased (p < 0.05) with time. It is concluded that (a) carbonation decreased the consumption of the 6% CHO beverage; (b) fluid homeostasis and thermo-regulation were unaffected by the solutions ingested; and (c) fluid consumption decreased with time, while ratings of fullness and thirst increased.

Adult↗