Gastric emptying during exercise: effects of heat stress and hypohydration

To determine the effects of acute heat stress, heat acclimation and hypohydration on the gastric emptying rate of water (W) during treadmill exercise, ten physically fit men ingested 400 ml of W before each of three 15 min bouts of exercise (treadmill, approximately 50% VO2max) on five separate occasions. Stomach contents were aspirated after each exercise bout. Before heat acclimation (ACC), experiments were performed in a neutral (18 degrees C), hot (49 degrees C) and warm (35 degrees C) environment. Subjects were euhydrated for all experiments before ACC. After ACC, the subjects completed two more experiments in the warm (35 degrees C) environment; one while euhydrated and a final one while hypohydrated (-5% of body weight). The volume of ingested water emptied into the intestines at the completion of each exercise bout was inversely correlated (P less than 0.01) with the rectal temperature (r = -0.76). The following new observations were made: 1) exercise in a hot (49 degrees C) environment impairs gastric emptying rate as compared with a neutral (18 degrees C) environment, 2) exercise in a warm (35 degrees C) environment does not significantly reduce gastric emptying before or after heat acclimation, but 3) exercise in a warm environment (35 degrees C) when hypohydrated reduces gastric emptying rate and stomach secretions. Reductions in gastric emptying appear to be related to the severity of the thermal strain induced by an exercise/heat stress.     

Effect of beverage osmolality on intestinal fluid absorption during exercise

To determine howosmolality of an orally ingested fluid-replacement beverage would alterintestinal fluid absorption from the duodenum and/or jejunumduring 85 min of cycle exercise (63.3 ± 0.9% peakO₂ uptake) in a cool environment(22°C), seven subjects (5 men, 2 women, peakO₂ uptake = 54.5 ± 3.8 ml · kg¹ · min¹) participated infour experiments separated by 1 wk in which they ingested a waterplacebo (WP) or one of three 6% carbohydrate (CHO) beveragesformulated to give mean osmolalities of 197, 295, or 414 mosmol/kgH₂O. CHO solutions alsocontained 17-18 meq Na⁺ and3.2 meq K⁺. Nasogastric andmultilumen tubes were fluoroscopically positioned in the gastric antrumand duodenojejunum, respectively. Subjects ingested a total of 23 ml/kgbody mass of the test solution, 20% (370 ± 9 ml) of this volume 5 min before exercise and 10% (185 ± 4 ml) every 10 min thereafter.By using the rate of gastric emptying as the rate of intestinalperfusion (G. P. Lambert, R. T. Chang, D. Joensen, X. Shi, R. W. Summers, H. P. Schedl, and C. V. Gisolfi. Int. J. Sports Med. 17: 48-55, 1996), intestinal absorption was determined by segmental perfusion from the duodenum (0-25 cm) and jejunum (25-50 cm). There were no differences(P > 0.05) in gastric emptying (mean18.1 ± 1.3 ml/min) or total fluid absorption (802 ± 109, 650 ± 52, 674 ± 62, and 633 ± 74 ml · 50 cm¹ · h¹for WP, hypo-, iso-, and hypertonic solutions, respectively) amongbeverages; but WP was absorbed faster(P < 0.05) from the duodenum than inthe jejunum. Of the total volume of fluid ingested, 82 ± 14, 74 ± 6, 76 ± 5, and 68 ± 7% were absorbed forWP, hypo-, iso-, and hypertonic beverages, respectively. There were nodifferences in urine production or percent change in plasma volumeamong solutions. We conclude that total fluid absorption of 6%CHO-electrolyte beverages from the duodenojejunum during exercise,within the osmotic range studied, is not different from WP.

     

Effect of delayed gastric emptying on fluoride absorption in the rat

The rate and site of fluoride (F) absorption were compared in fasted 350 g male rats given 50 micrograms F (as NaF) in either water or a 7.5% pectin solution. Absorption was measured at intervals up to 2 h following gastric intubation. Gastric emptying was measured by inclusion of 14C-PEG in the F solution. The extent of gastric F absorption was derived from rates of gastric emptying (14C-PEG loss) and F loss. Pectin markedly slowed gastric emptying, but by 2 h, more than 90% of the solution had passed into the small intestine in both groups, and F absorption exceeded 90% in both groups. The rate of F absorption was initially much slower in the pectin group than in the group given F in water, and plasma F concentration increased more slowly and reached a lower maximum value. Absorption from the stomach was greater in the pectin group, but still accounted for only approx 25% of total gastrointestinal absorption. The reduced rate of F absorption and slower rise in plasma F concentration accompanying delayed gastric emptying indicate that passage of F into the small intestine is the major factor in rapid F absorption.     

Gastric emptying, absorption, and carbohydrate oxidation during prolonged exercise.

This study was designed to examine aspects of digestive function that may limit assimilation of water and oxidation of orally ingested carbohydrate (CHO) during exercise. Eight males completed a crossover study in which each cycled on four occasions for 80 min at 70% maximal O2 consumption. Beverage was consumed at 0, 20, 40, and 60 min. Beverages were water, 4.5% glucose (4.5G), 17% glucose (17G), and 17% maltodextrin (17MD). CHO beverages contained 20 meq/l NaCl and were 13C enriched to measure exogenous CHO oxidation. Gastric (beverage) volume was measured at 80 min. Water uptake was estimated by including 2H2O in the beverage and measuring 2H accumulation in blood. Jejunal perfusion tests were conducted at rest with the same subjects and beverages. In 60 min, 1,294 +/- 31 (SE) ml were ingested; at 80 min, volumes emptied with H2O (1,257 +/- 32 ml) and 4.5G (1,223 +/- 32 ml) were greater than with 17G (781 +/- 56 ml) and 17MD (864 +/- 71 ml; P less than 0.05). Total CHO oxidized was similar with all beverages, but there was a greater increase in exogenous CHO oxidation over time with 17G and 17MD than with 4.5G; 54, 19, and 18% of the CHO ingested with 4.5G, 17G, and 17MD, respectively, was oxidized. This represents 57, 32, and 27%, respectively, of the CHO emptied from the stomach. 2H accumulation in the blood was more rapid with H2O and 4.5G than with 17G or 17MD. Net jejunal water absorption was greater from 4.5G than from water. Net water absorption was also observed from 17MD, whereas net secretion was observed with 17G.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermoregulatory and blood responses during exercise at graded hypohydration levels

We studied the effects of graded hypohydration levels on thermoregulatory and blood responses during exercise in the heat. Eight heat-acclimated male subjects attempted four heat-stress tests (HSTs). One HST was attempted during euhydration, and three HSTs were attempted while the subjects were hypohydrated by 3, 5, and 7% of their body weight. Hypohydration was achieved by an exercise-heat regimen on the day prior to each HST. After 30 min of rest in a 20 degrees C antechamber the HST consisted of a 140-min exposure (4 repeats of 10 min rest and 25 min treadmill walking) in a hot-dry (49 degrees C, 20% relative humidity) environment. The following observations were made: 1) a low-to-moderate hypohydration level primarily reduced plasma volume with little effect on plasma osmolality, whereas a more severe hypohydration level resulted in no further plasma volume reduction but a large increment in plasma osmolality; 2) core temperature and heart rate responses increased with severity of hypohydration; 3) sweating rate responses for a given rectal temperature were systematically decreased with severity of hypohydration; and 4) the reduction in sweating rate was more strongly associated with plasma hyperosmolality than hypovolemia. In conclusion, an individual's thermal strain increases linearly with the severity of hypohydration during exercise in the heat, and plasma hyperosmolality influences the reduction in sweating more profoundly than hypovolemia.     

B-type natriuretic peptide decreases gastric emptying and absorption

Natriuretic peptides have been shown to decrease contractility of isolated gastric smooth muscle cells. However there is a paucity of research showing whether this effect has functional significance in the whole animal. The objective of this study was to test whether intravenously administered B-type Natriuretic Peptide (BNP) has an effect on gastric emptying and/or absorption in a whole animal mouse model. C57BL/6-Wild-type (WT) and Natriuretic Peptide Receptor type A (NPR-A) knockout (KO) mice were used in these studies. Gastric contractility was examined in anesthetized mice before and after BNP vs. vehicle injection. Gastric emptying of gavage fed 70 Kilo Dalton (kDa) FITC-dextran and absorption of 4 kDa FITC-dextran were compared in BNP vs. vehicle treated conscious WT and KO mice. BNP decreased gastric contractility (measured in change in intragastric pressure) from 2.26 +/- 0.29 to 1.44 +/- 0.11 mmHg (P < 0.05), pressure returned to 2.08 +/- 0.17 after 5 BNP half-lives (P < 0.05). There was no significant change in the vehicle or KO. BNP also decreased gastric emptying in WT mice compared to vehicle, 87.8 +/- 0.8% vs. 97.3 +/- 1.04% (P < 0.05) and this effect showed a dose-response relationship. In KO mice emptying was 95.8 +/- 0.5% (BNP) vs. 91.7 +/- 0.7% (Vehicle) (P > 0.05). The absorption in WT mice was 28.2 +/- 7.8 (relative fluorescence units) for BNP vs. 91 +/- 25.9 for vehicle (P < 0.05). For KO mice absorption was 64.3 +/- 14.9 for BNP vs. 60.6 +/- 17.4 for vehicle (P > 0.05). The results show that BNP decreases intragastric pressure, emptying and absorption by acting via the NPR-A receptor. We postulate that this effect is aimed at decreasing preload through decreased water and electrolyte absorption from the GI tract and may also be responsible for the symptoms of impaired gastrointestinal function observed in heart failure patients.     

Effect of the secretin family of peptides on gastric emptying and small intestinal transit in rats

We have compared the effects of the secretin family of peptides and their synthetic fragments on gastric emptying (GE) and small intestinal transit (SIT) using an unanesthetized rat model which simultaneously measures the GE and SIT of both solids and liquids. The meal consisting of 5% polyethylene glycol w/v, 5% Indian ink v/v and 20 non-digestible plastic beads was given intragastrically 10 minutes after the intraperitoneal injection of 0.5 ml of saline or peptides (2 and 5 micrograms/kg). Plasma secretin and the immunospecificity of secretin fragments were determined. In control rats, the t1/2 for the GE of both solids and liquids were 56 +/- 3.8 and 19 +/- 2.3 minutes, respectively. Liquids emptied faster than the solids and liquids travelled ahead of the solids in the intestine. Secretin (5 micrograms/kg) inhibited GE of both solids and liquids by 33-37%. Secretin delayed the SIT of the meal by approximately 35%. Fragments of secretin and of VIP had no effect on GE and SIT of both solids and liquids. The whole molecule of secretin was required to inhibit GE and to delay SIT of solids and liquids. Glucagon, PHI and growth hormone releasing factor (GHRF1-44) inhibited GE and SIT of both solids and liquids. For all peptides tested, the inhibition of SIT was proportional to the inhibition of GE suggesting that the prolongation of SIT was secondary to delayed GE. These observations indicate that the peptides of the secretin family inhibit GE and prolong SIT. Thus, the structural requirement required for the secretin family of peptides to effect their motor actions on the stomach is similar to that required for pancreatic enzyme secretion.     

Some observations on the effects of heat,exercise and hypohydration upon involuntary hypohydration in man

Four male subjects at a high level of physical fitness were put on a controlled diet 4 days prior to a 4-hr exposure in a hot room(49°C) in separate experiments at rest or with exercise on a treadmill and free or no access to drinking water.The experiments were repeated at 24°C.Each experiment was followed by a recovery period of 8 hr. The water intake during the heat exposure was roughly proportional to the work load. The rate of water consumption during the recovery period was independent of the level of hypohydration. Previously hypohydrated men took longer to regain their water debt than previously hydrated men.

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Zusammenfassung Vier gut tränierte Personen wurden nach 4 Tagen Ernährung mit einer Kontrolldiät 4 Stunden in einer Klimakammer bei 49°C in Ruhe oder mit Belastung (Laufband)mit oder ohne Wasser zum Trinken exponiert.Die Werte wurden verglichen mit dem Verhalten der gleichen Personen bei 24°C. Den Exponierungsversuchen folgte eine Erholungsperiode von 8 Stunden bei 24°C. Die Wasserbedarf während der Hitzeexponierung war ungefähr proportional der körperlichen Leistung. Die Geschwindigkeit der Wasseraufnahme in der Erholungsphase war unabhängig von den Ausmass der Hypohydration. Die Auffüllung der Wasserschuld dauerte mehrere Stunden. Unabhängig von der Ausmass der Wasserschuld stieg die Wasseraufnahme während der Mahlzeiten an.

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Resume Après avoir été mis durant 4 jours à une diète contrôlée, 4 personnes bien entraînées ont été placées dans une chambre climatisée. Ces personnes y restèrent durant 4 hr par 49°C avec ous sans eau à boire, soit au repos,soit en effectuant un effort (roue). On a alors comparé les résultats obtenus à ceux des mêmes personnes soumises aux mêmes épreuves, mais par 24°C. Les expositions au chaud furent suivies de périodes de repos de 8 hr par 24°C. Les besoins en eau furent, lors des essais, environ proportionnels à l'effort fourni. La rapidité avec laquelle l'eau fut absorbée pendant la phase de récupération fut indépendante du degré de déshydratation. La compensation du déficit hydrique dura plusieurs heures. Indépendemment de l'importance du déficit hydrique, on a constaté une augmentation de la consommation en eau durant les repas.

     

Effect of CCK and its antagonists on gastric emptying

Cholecystokinin (CCK) belongs to the group of substances known as brain-gut peptides: it functions both as a neuropeptide and a gut hormone. The peptide and its synthetic derivatives (like for instance CCK-8 and the amphibian counterpart caerulein) significantly delay emptying of gastric contents in both animals and humans. The fact that CCK, in doses mimicking postprandial plasma levels, strongly affects emptying rate suggests the peptide to be a physiologic regulator of gastric emptying. Unfortunately, clear definition of the role of CCK in the physiology of gastric motor activity has long been hampered by the lack of specific and potent non-peptide antagonists of CCK-receptors. The availability of such compounds has stimulated a broad array of investigations into the physiological actions of this hormone and examination of its putative role in certain diseases. This paper summarizes the available data concerning the effect of CCK and its antagonists on gastric emptying. The use of selective CCK-antagonists has allowed to establish that the gastric motor effect of the peptide is direct and mediated through the stimulation of CCK-A receptors. As a consequence, CCK-A antagonism results in acceleration of emptying rate under certain experimental and clinical conditions. This peculiar pharmacologic effect of CCK-A antagonists, which could be useful in the treatment of functional dyspepsia (idiopathic or diabetic), gastroparesis and gastro-esophageal reflux disease (where patients often display a delayed emptying rate of solid food) needs to be further investigated, in order to fully explore their potential as gastrokinetic drugs.     

Effect of the menstrual cycle on gastric emptying

Gastric emptying of a radiolabelled solid meal was studied in 19 women. The gastric emptying curves were analyzed with the use of a power-exponential fitting, and the results were related to the phases of the menstrual cycle. No significant differences between the phases of the menstrual cycle were found when the rates of gastric emptying were compared. However, different emptying patterns in each phase of menstrual cycle were revealed by the analysis of the curve shape parameter, S. The physiological and clinical relevance of the findings is discussed.     

Effect of ghrelin on gastric myoelectric activity and gastric emptying in rats

Ghrelin is a recently discovered peptide in the endocrine cells of the stomach, which may stimulate gastric motility via the vagal nerve pathway. However, the mechanism of ghrelin-induced changes in gastrointestinal motility has not been clearly defined. The purpose of this study was to investigate the pharmacological effects of ghrelin on gastric myoelectrical activity and gastric emptying in rats, and to investigate whether cholinergic activity is involved in the effects of ghrelin. The study was performed on Sprague-Dawley rats implanted with serosal electrodes for electrogastrographic recording. Gastric slow waves were recorded from fasting rats at baseline and after injection of saline, ghrelin, atropine, or atropine+ghrelin. Gastric emptying of non-caloric liquid was measured by the spectrophotometric method in conscious rats. Intravenous administration of rat ghrelin (20 microg/kg) increased not only dominant frequency, dominant power and regularity of the gastric slow wave but also the gastric emptying rate when compared with the control rats (P<0.01, P<0.05, P<0.05, P<0.001 respectively). These stimulatory actions of ghrelin on both gastric myoelectrical activity and gastric emptying were not fully eliminated by pretreatment with atropine sulphate. These results taken together suggest that ghrelin may play a physiological role in the enteric neurotransmission controlling gastric contractions in rats.     

Effect of cigarette smoking on gastric emptying.

Gastric emptying after a test meal was studied in 17 normal volunteers--10 habitual smokers and seven non-smokers. The solid component of the test meal was labelled with technetium and the liquid component with indium. After one meal the habitual smokers smoked two cigarettes. Emptying curves were produced for both technetium and indium, and the differences between curves for meals with and without cigarettes were analysed. Cigarette smoking accelerated the rate at which the liquid component of a meal left the stomach. This may be important in the pathogenesis of duodneal ulcer and the delay in healing caused by cigarette smoking.     

Effects of cycle exercise on intestinal absorption in humans.

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.     

Observations on the relation between alcohol absorption and the rate of gastric emptying.

Alcohol (ethanol) is absorbed slowly from the stomach and rapidly from the small intestine, and the rate of its absorption depends on the rate of gastric emptying. When gastric emptying is fast, the absorption of alcohol is fast. When gastric emptying is slow the absorption of alcohol is delayed and peak blood alcohol concentrations are reduced. Alterations of the gastric emptying rate, which may have a physiologic, pharmacologic or pathologic cause, markedly influence the rate of alcohol absorption. The gastric emptying rate makes an important contribution to inter- and intraindividual variations in the rate of alcohol absorption and therefore the timing and magnitude of the acute intoxicating effect of an oral dose of alcohol.