The effect of alcohol on zinc absorption

Two methods of intestinal perfusion are described and used to study the effecs of alcohol on zinc absorption in the rat small intestine. The first method used perfusion of the lumen of the rat small intestinein situ without interruption of the vascular supply. During perfusion with a zinc-containing medium (with and without alcohol), alcohol was found to have no effect on net zinc uptake from the lumen of the intestine. However, there were significantly higher serum zinc concentrations recorded in the rats perfused wih the zinc and alcohol, 28.8 μmol/L, when compared with a group perfused without alcohol, 19.1 μmol/L (P < 0.01). The second method used simultaneous perfusion of the lumen of the rat small intestine, with constant-rate perfusion of the vascular bed with an artificial blood supply. In this experiment with a zinc-containing medium, with and without alcohol, there was no difference noted in zinc absorption from the lumen of the intestine, or release into the artificial blood supply. Therefore, in conclusion, alcohol does not appear to directly influence zinc absorption by the mucosal cells of the small intestine.     

Effect of size of Trichinella spiralis (Nematode) infections on glucose and ion transport in the rat intestine

An in vivo perfusion technique, using 3 intestinal loops representing the anterior, mid and posterior regions of the rat small intestine, was used to determine intestinal glucose uptake 5 days after infection with Trichinella spiralis. At high levels of infection (3,000 and 6,000 larvae/rat) net glucose absorption by the intestinal mucosa was significantly impaired in all regions of the small intestine when compared to uninfected controls. At low levels of infection (50 larvae/rat) glucose uptake by the mucosa was significantly enhanced in all 3 regions of the small intestine. Intermediate levels of infections (200-1,000 larvae/rat) also enhanced glucose uptake, but only in the anterior regions of the small intestine. When washings from the small intestine of rats infected with 50 larvae/rat were added to the perfusion fluid used on uninfected rats, glucose uptake was also significantly enhanced. These results suggest that at low levels of infection the intestinal lumen contains a metabolite which may affect the mucosal transport of glucose and the related fluxes of H2O, Na+, Cl-, and K+, in the rat intestine. Luminal [H+] and pCO2 decreased from the proximal to distal regions of the small intestine following perfusion; pO2 was significantly decreased in the proximal and distal regions.     

The release of GLP-1 and ghrelin, but not GIP and CCK, by glucose is dependent upon the length of small intestine exposed

Previous observations suggest that glucagon-like peptide-1 (GLP-1) is released into the bloodstream only when dietary carbohydrate enters the duodenum at rates that exceed the absorptive capacity of the proximal small intestine to contact GLP-1 bearing mucosa in more distal bowel. The aims of this study were to determine the effects of modifying the length of small intestine exposed to glucose on plasma concentrations of GLP-1 and also glucose-dependent insulinotropic peptide (GIP), insulin, cholecystokinin (CCK) and ghrelin, and antropyloric pressures. Glucose was infused at 3.5 kcal/min into the duodenum of eight healthy males (age 18-59 yr) over 60 min on the first day into an isolated 60-cm segment of the proximal small intestine ("short-segment infusion"); on the second day, the same amount of glucose was infused with access to the entire small intestine ("long-segment infusion"). Plasma GLP-1 increased and ghrelin decreased (P < 0.05 for both) during the long-, but not the short-, segment infusion. By contrast, increases in plasma CCK and GIP did not differ between days. The rises in blood glucose and plasma insulin were greater during the long- than during the short-segment infusion (P < 0.05). During the long- but not the short-segment infusion, antral pressure waves (PWs) were suppressed (P < 0.05). Isolated pyloric PWs and basal pyloric pressure were stimulated on both days. In conclusion, the release of GLP-1 and ghrelin, but not CCK and GIP, is dependent upon >60 cm of the intestine being exposed to glucose.     

Satiety, fasting, and refeeding study of absorption in rats

In the rat, small intestine preparation was studied with the aid of our modification of Na(+)-dependent nutrient absorption short-circuit current method. In experiments on rats, it was shown that reaction of the gut to animal state changes (fasting, satiety and refeeding) depended on its medial or distal localization. Active Na+ absorption in medial part of small intestine after refeeding rose 3-6-fold depending on period of previous fasting (2 or 5 days). Two states of satiety were elucidated: when the rats were in cage with meal and after refeeding following a 5-day fasting; at least in distal small intestine, absorption of nutrients in the latter state was much higher. Fast nutrient adaptation (approximately 30 min) of absorption was revealed, second responses of short-circuit current to glyala were 3.4-fold higher than the first one: 33.4 +/- 9.7 (n = 6) and 9.9 +/- 2.9 microA/cm2 (n = 6) (P < 0.05). It is possible that increased nutrients (glucose and aminoacids) entering in mucose after the 5th day refeeding play role as a primary signal for change of animal behavior.     

Structural and functional analysis of glucose adsorption at high maltose concentrations in the rat small intestine in vivo

To elucidate the mechanism of glucose absorption at high substrate concentrations, we studied structural and ultrastructural peculiarities of enterocytes arranged at different levels along the intestinal villus. The preparations were obtained from an isolated segment of the rat small intestine after its perfusion with maltose solutions with both low (25 mM) and high (100 mM) concentrations, respectively. Under conditions of chronic experiment at high substrate concentration, an enlargement of intercellular clefts, indicating glucose absorption, occurred in deeper areas of the villus. Besides, also in chronic experiment, we studied kinetics of maltose hydrolysis and derived glucose absorption in the isolated segment of the rat small intestine after its perfusion with maltose at superhigh (up to 200 mM) initial concentrations. Based on these data, a conclusion is made that active transport is the main mechanism of absorption of glucose derived from maltose hydrolysis, operating both at low disaccharide concentrations, and in the range of its superhigh (up to 200 mM) concentrations.     

Seasonal Variation in Amount of Unabsorbed Dietary Carbohydrate from the Intestine after Breakfast in Japanese Subjects

We previously showed that daytime dim‐light exposure has a negative effect on the efficiency of dietary carbohydrate absorption in the evening, whereas evening‐time dim‐light exposure has a beneficial effect. These results suggest that seasonal changes in the environmental light may affect gastrointestinal activity, and that there might, therefore, be seasonal variation in the efficiency of dietary carbohydrate absorption from the intestine. In order to prove this hypothesis, we measured the amount of dietary carbohydrate unabsorbed from the intestine after a breakfast in healthy female Japanese subjects during the four seasons of the year. We estimated the amount of unabsorbed dietary carbohydrate by the breath hydrogen test, which measures the amount of hydrogen in exhaled air. A 6 g solution of lactosucrose, an indigestible trisaccharide, was used for comparison. Two groups of subjects, 12 subjects in Osaka and 14 subjects in Nagano, were studied in the winter (January to February), spring (April to May), summer (July to August), and autumn (October to November) of 2004. We found the following results: (1) In no season were there any significant differences between the two subgroups in the orocecal transit time of the breakfast and the lactosucrose solution. Nor were there any significant differences in the amount of unabsorbed dietary carbohydrate from the breakfast. (2) Using the pooled data of the total of 26 subjects, there was no significant seasonal variation in the orocecal transit time of the breakfast or the lactosucrose solution. (3) There was a significant seasonal variation in the amount of unabsorbed dietary carbohydrate from the breakfast. (4) The amount of unabsorbed dietary carbohydrate from the breakfast was largest in winter and smallest in autumn. Results in spring and in summer were similar and intermediate between those in winter and autumn. Post hoc multiple comparison tests showed that the amount of unabsorbed dietary carbohydrate in winter was significantly larger than in autumn. (5) In winter, the average ratio of the amount of unabsorbed dietary carbohydrate to the total amount of carbohydrate in the breakfast was about 12%; in autumn it was about 6%. These results clearly show that there is seasonal variation in the efficiency of intestinal dietary carbohydrate absorption among young female Japanese subjects.     

The influence of protein starvation on hydrolytic and transport characteristics of the rat small intestine in chronic experiments

Time dynamics of maltose, glycylglycine, glucose, and glycine hydrolysis and absorption in isolated loop of the small intestine was studied in chronic experiments on Wistar rats (group 1) after their transition from the standard diet to the protein-free one with enhanced content of carbohydrates. During protein starvation, there were different changes in the rates of glucose and glycine absorption, and glycylglycine hydrolysis and absorption in isolated intestinal loop, but to the end of the 2nd week they returned to the initial levels (for glucose and glycylglycine) or increased (for glycine). The rates of maltose hydrolysis and derived glucose absorption remained at the initial levels for the first days of protein starvation, decreased on the 5th day, and did not change afterwards. Maltase, alkaline phosphatase, and amino peptidase M activities, determined in homogenates of the small intestinal mucosa (per g of the tissue) after 2 weeks of protein starvation, were lower in the rats of group 1 in comparison with the rats of group 2, kept on the standard diet. Thus, under protein deficiency the hydrolytic and absorptive capacities of the small intestine correspond to both ingested food composition, and body requirements.     

Immunohistochemical localization of Na+-dependent glucose transporter in the rat digestive tract

Summary Glucose is actively absorbed in the intestine by the action of the Na⁺-dependent glucose transporter. Using an antibody against the rabbit intestinal Na⁺-dependent glucose transporter (SGLT1), we examined the localization of SGLT1 immunohistochemically along the rat digestive tract (oesophagus, stomach, duodenum, jejunum, ileum, colon and rectum). SGLT1 was detected in the small intestine (duodenum, jejunum and ileum), but not in the oesophagus, stomach, colon or rectum. SGLT1 was localized at the brush border of the absorptive epithelium cells in the small intestine. Electron microscopical examination showed that SGLT1 was localized at the apical plasma membrane of the absorptive epithelial cells. SGLT1 was not detected at the basolateral plasma membrane. Along the crypt-villus axis, all the absorptive epithelial cells in the villus were positive for SGLT1, whose amount increased from the bottom of the villus to its tip. On the other hand, cells in the crypts exhibited little or no staining for SGLT1. Goblet cells scattered throughout the intestinal epithelium were negative for SGLT1. These observations show that SGLT1 is specific to the apical plasma membrane of differentiated absorptive epithelial cells in the small intestine, and suggest that active uptake of glucose occurs mainly in the absorptive epithelial cells in the small intestine.     

Effect of Evening Exposure to Dim or Bright Light on the Digestion of Carbohydrate in the Supper Meal

In a previous study we found that daytime exposure to bright as compared to dim light exerted a beneficial effect on the digestion of the evening meal. This finding prompted us to examine whether the digestion of the evening meal is also affected by evening light intensity. Subjects lived in light of 200 lux during the daytime (08:00–17:00 h) and took their evening meal at 17:00 h under 20 lux (evening dim‐light condition: 17:00–02:00 h) or 2000 lux (evening bright‐light condition: 17:00–02:00 h) until retiring at 02:00 h. Assessment of carbohydrate digestion of the evening meal was accomplished by a breath hydrogen test that is indicative of the malabsorption of dietary carbohydrate. Hydrogen excretion in the breath in the evening under the dim‐light condition was significantly less than under the bright‐light condition (p < 0.05). This finding is the opposite to that obtained in previous experiments in which subjects were exposed to the different intensities of light during the daytime, and indicates that the exposure to dim light in the evening exerts a better effect on carbohydrate digestion in the evening meal than does the exposure to bright light.     

Study of glucose concentrated solution consumption in rats and simulation of glucose distribution along the intestine

Free ingestion of glucose solution (200 or 400 g/l) by Wistar rats, previously starved for 18-20 Hrs, was investigated in two groups of the animals: with intact small intestine (group 1, n = 9), and a shortened small intestine following the Thiry-Wella isolation of its one third proximal part (group 2, n = 9). In the rats of the group 2, the isolated intestinal loops were perfused in chronic experiments with soulutions of different glucose concentrations to estimate a permeability of the pre-epithelial ("unstirred") layer and "true" kinetic constants of glucose active transport. The rate of glusouse ingestion was found to be 1.3-fold as high in the of rats fgroup 1 than in the rats of group 2 (p < 0.01). According to results of mathematical modeling, the rate of glucose ingestion by rats corresponds to glucose concentration in the initial solutions and to the absorbing capacity of the small intestine due to the substrate regulation of gastric emptying. The model predicts that, during free ingestion by rats of 400 g/l (2200 mM) glucose solution, the substrate concentration in the intestinal lumen under steady state conditions hardly exceeds 75 mM. This fact contradicts a recently proposed hypothesis about a facilitated transport mediated by GLUT2 as the main mechanism of glucose absorption in the small intestine under normal conditions.     

Kinetic parameters of maltose hydrolysis and glucose intake in the rat small intestine in a chronic experiment

"True" (corrected for the influence of the pre-epithelial layer) kinetic constants of maltose hydrolysis (Km and Vmax) and Glucose active transport (Kt and Jmax) in the isolated loop of the rat small intestine in chronic experiments were determined using a new mathematical approach. The Km (4.260.25 mM) does not differ from that, obtained in in vitro experiments on the homogenates of mucous membrane taken from the same intestinal loops, and the Vmax (0.72 +/- 0.07 mol/(min.cm)) is 1.7 times lower than that in in vitro experiments. The Kt and Jmax values are 3.18 +/- 0.68 mM and 0.73 +/- 0.07 mol/(min.cm), resp. The estimated values of Km, Kt and Vmax are in accordance with the corresponding published data, whereas the Jmax is several times higher than the value generally believed on the basis of acute experiments in vivo. A high level of glucose absorption in the small intestine of unanesthetized animals is achieved mainly due to a high permeability of the pre-epithelial layer and a high capacity of the active transport as a major mechanism of glucose absorption in the small intestine under normal conditions.     

Intestinal absorption and metabolism of a soluble flavonoid, αG-rutin,in portal cannulated rats

A highly soluble quercetin glycoside, αG-rutin, is a glucose adduct of insoluble rutin, and intestinal absorption and metabolism of αG-rutin has not been known. We investigated the intestinal absorption and metabolism of αG-rutin by using portal and duodenal cannulated rats and the isolated rat intestinal mucosa. After a duodenal instillation of αG-rutin (150 μmol), intact αG-rutin, rutin and quercetin were appeared in the portal blood and these concentrations were similarly increased at 15 min. Portal quercetin reached a peak value at 60 min, and the value was higher than those of αG-rutin and rutin at that time. Quercetin-conjugates were also increased 30 min after the instillation. The remaining of αG-rutin metabolites, mainly rutin, in the intestine were 58% of instilled αG-rutin after 150 min. In the experiment by using the isolated mucosa of the jejunum, ileum and cecum, αG-rutin and rutin, but not quercetin, appeared in the serosal sides of all segments, and they were increased linearly from 10 to 100 mmol/l of mucosal αG-rutin. We also showed portal injected αG-rutin was very rapidly cleared from the blood, and appeared a large amount of conjugates. In conclusion, a soluble flavonoid-glycoside, αG-rutin, was absorbed as glycosides into the portal blood. A part of αG-rutin was hydrolyzed to rutin, but not to aglycone, through the intestine.     

The acute regulation of glucose absorption, transport and metabolism in rat small intestine by insulin in vivo.

The effect of acute changes in insulin concentrations in vivo on the absorption, transport and metabolism of glucose by rat small intestine in vitro was investigated. Within 2 min of the injection of normal anaesthetized rats with anti-insulin serum, lactate production and glucose metabolism were respectively diminished to 28% and 21% of normal and the conversion of glucose into lactate became quantitative. These changes correlated with the inhibition of two mucosal enzymes, namely the insulin-sensitive enzyme pyruvate dehydrogenase, and phosphofructokinase, which was shown by cross-over measurements to be the rate-limiting enzyme of glycolysis in mucosa. The proportion of glucose translocated unchanged from the luminal perfusate to the serosal medium was simultaneously increased from 45% to 80%. All the changes produced by insulin deficiency were completely reversed with 2 min when antiserum was neutralized by injection of insulin in vivo. The absorption and transport of 3-O-methylglucose were unaffected by insulin. It is concluded that glucose metabolism in rat small intestine is subject to short-term regulation by insulin in vivo and that glucose absorption and transport are regulated indirectly in response to changes in metabolism. Moreover, transport and metabolism compensate in such a way as to deliver the maximal 'effective' amount of glucose to the blood, whether as glucose itself or as lactate for hepatic gluconeogenesis.     

The influence of estradiol and diet on small intestinal glucose transport in ovariectomized rats

Although gender differences exist for intestinal absorption of nutrients and drugs, the possible role estradiol may play in modulating nutrient transport has not been established. Therefore, small intestine glucose transport was measured 1 week after administering estradiol to ovariectomized rats fed diets high in carbohydrate (C) or protein (P). Rats treated with estradiol ate 21% less (P<0.05) and lost body mass (7%; P<0.05) but did not have smaller intestines. Administration of estradiol increased rates of glucose transport, but only when the rats were fed the C diet. These findings indicate that estradiol causes a disconnect between food intake and the dimensions and nutrient transport capacities of the small intestine. Furthermore, the responses to estradiol are influenced by diet composition, are not of the same magnitude for rats and dogs, and can be predicted to affect systemic availability of nutrients and drugs.     

Effect of phloretin and phloridzin on properties of digestion and absorption in the rat small intestine

Experiments in vitro on everted sacs of rat small intestine have shown that phloretin (an inhibitor of basolatheral glucose GLUT2 transporter) added from mucosal side of the sacs decreases release of glucose from enterocytes into serosal fluid without changing glucose accumulation in tissue of the preparations. Addition of phloridzin (an inhibitor of Na⁺ and glucose co-transporter SGLT1) from mucosal side inhibited both glucose accumulation in the tissue and its release into serosal fluid. Unspecific effects of phloretin and phloridzin on activities of several digestive enzymes (in particular, alkaline phosphatase, amino peptidase, and glycyl-L-leucine dipeptidase) has been revealed in homogenates of the rat small intestine mucosa. In chronic experiments on rats, absorption of glycine from the isolated small intestinal loop was inhibited in the presence of phloretin in perfusate. The obtained results indicate that the experimental approach of inhibition of glucose absorption by phloretin used from mucosal side in vitro appears to give a significant overestimation of contribution of facilitated diffusion (with participation of the GLUT2 transporter inserted in the apical enterocyte membrane) to glucose transport across this membrane. Thus, the role of the GLUT2 transporter in the mechanism of glucose absorption in the small intestine under its physiological conditions does not seem to be as great as it is thought by the authors of the recently proposed hypothesis.     

Nippostrongylus brasiliensis: malabsorption in experimentally infected rats

Glucose absorption and net small intestinal water movement were examined in rats infected with Nippostrongylus brasiliensis at Days 4, 6, 9, 13, and 19 after inoculation. Rats were infected with 4 X 10(3) N. brasiliensis third stage larvae. The entire small intestine was divided into three segments and each segment perfused simultaneously in vivo with Krebs-Ringer phosphate buffer containing 80 mM glucose, 6 X 10(5) dpm/ml [3H]glucose, and 6.2 X 10(3) dpm/ml [14C]polyethylene glycol. Rats perfused on Days 6, 9, 13, and 19 after inoculation showed a significant (P less than 0.05) decrease in glucose absorption rates from all three segments of the small intestine when compared to uninfected controls. In the three segments of uninfected rat small intestine and those perfused on Days 4, 13, and 19 after inoculation, net absorption of water occurred. However, in the proximal and distal segments perfused on Day 6 and the proximal segment perfused on Day 9, net water movement into the lumen occurred. This is the first report of depressed glucose absorption along the entire length of the small intestine during nippostrongylosis and contradicts previous reports of unaltered net glucose absorption in response to this parasite.     

大鼠红细胞葡萄糖代谢的异头物选择性

为研究大鼠红细胞对葡萄糖利用的异头物选择性及其作用机制,应用大鼠红细胞,对葡萄糖的两种异头物作了异构化速率、乳酸生成量、内流速度和大鼠红细胞已糖激酶作用下的磷酸化速度等进行了测定．结果指出,３７℃时大鼠红细胞的Ｄ－葡萄糖β－异头物和α－异头物代谢成乳酸的速度分别是０．２７μｍｏｌ／ｇＨｂ（３ｍｉｎ）和０．２１μｍｏｌ／ｇＨｂ（３ｍｉｎ）,即前者快于后者３０％．同时β－Ｄ－葡萄糖向红细胞内转运速度也快于后者：分别是５．０和３．５μｍｏｌ／ｇＨｂ（３ｍｉｎ）．大鼠红细胞已糖激酶的葡萄糖磷酸化速率实验结果指出：β－异头物比α－异头物快３０％;对于该两种异头物已糖激酶的Ｋｍ值均为５３μｍｏｌ／Ｌ．红细胞与α－和β－Ｄ－葡萄糖保温１ｍｉｎ后,其葡萄糖浓度均达到１ｍｍｏｌ／Ｌ左右,说明至少在１ｍｉｎ内对于已糖激酶的磷酸化此两种异头物的葡萄糖浓度均已饱和．这些结果提示,大鼠红细胞葡萄糖利用的β－异头物优选性主要与其磷酸化速度有关,而与其转运速度关系不大．     

Seasonal variation in amount of unabsorbed dietary carbohydrate from the intestine after breakfast in Japanese subjects

We previously showed that daytime dim-light exposure has a negative effect on the efficiency of dietary carbohydrate absorption in the evening, whereas evening-time dim-light exposure has a beneficial effect. These results suggest that seasonal changes in the environmental light may affect gastrointestinal activity, and that there might, therefore, be seasonal variation in the efficiency of dietary carbohydrate absorption from the intestine. In order to prove this hypothesis, we measured the amount of dietary carbohydrate unabsorbed from the intestine after a breakfast in healthy female Japanese subjects during the four seasons of the year. We estimated the amount of unabsorbed dietary carbohydrate by the breath hydrogen test, which measures the amount of hydrogen in exhaled air. A 6 g solution of lactosucrose, an indigestible trisaccharide, was used for comparison. Two groups of subjects, 12 subjects in Osaka and 14 subjects in Nagano, were studied in the winter (January to February), spring (April to May), summer (July to August), and autumn (October to November) of 2004. We found the following results: (1) In no season were there any significant differences between the two subgroups in the orocecal transit time of the breakfast and the lactosucrose solution. Nor were there any significant differences in the amount of unabsorbed dietary carbohydrate from the breakfast. (2) Using the pooled data of the total of 26 subjects, there was no significant seasonal variation in the orocecal transit time of the breakfast or the lactosucrose solution. (3) There was a significant seasonal variation in the amount of unabsorbed dietary carbohydrate from the breakfast. (4) The amount of unabsorbed dietary carbohydrate from the breakfast was largest in winter and smallest in autumn. Results in spring and in summer were similar and intermediate between those in winter and autumn. Post hoc multiple comparison tests showed that the amount of unabsorbed dietary carbohydrate in winter was significantly larger than in autumn. (5) In winter, the average ratio of the amount of unabsorbed dietary carbohydrate to the total amount of carbohydrate in the breakfast was about 12%; in autumn it was about 6%. These results clearly show that there is seasonal variation in the efficiency of intestinal dietary carbohydrate absorption among young female Japanese subjects.     

Enhanced glucose absorption in the rat small intestine following repeated doses of 5-fluorouracil

Many studies demonstrated that 5-fluorouracil (5-FU) treatment of rodents caused the damage of small intestine, resulting in the malabsorption, while we recently found that repeated administration of 5-FU to rats increased Na(+)-dependent glucose absorption in the small intestine. This study investigated the cause of enhanced glucose absorption. 3-O-methyl-d-glucose (3-OMG) absorption was examined using the everted intestine technique. d-Glucose uptake, phlorizin binding, Western blot analysis and membrane fluidity were examined using small intestinal brush-border membrane vesicles (BBMV). Repeated oral administration of 5-FU to rats increased Na(+)-dependent 3-OMG absorption in the small intestine, while alkaline phosphatase activity in the small intestine decreased. Na(+)/K(+)-ATPase activity of 5-FU-treated rats was about three-fold higher than that of control rats. Although the amount of Na(+)-dependent glucose co-transporter (SGLT1) in 5-FU-treated rats decreased, the overshoot magnitude of d-glucose uptake in BBMV was not altered. Maximum binding of phlorizin in 5-FU-treated rats was 1.5-fold larger than that of control rats, but not altered the maximal rate of d-glucose absorption, Michaelis constant of d-glucose and dissociation constant of phlorizin. The membrane fluidity of 5-FU-treated rats increased. The enhanced d-glucose absorption in 5-FU-treated rats seems to occur secondarily due to the activation of Na(+)/K(+)-ATPase activity in basolateral membranes (BLM). Because the amounts of SGLT1 in 5-FU-treated rats decreased, the increase of turnover rate of SGLT1 and/or an expression of unknown Na(+)-dependent glucose co-transporter with high affinity for d-glucose and phlorizin sensitivity would contribute to the enhancement of d-glucose transport in 5-FU-treated rats.