Intestinal glucose absorption in calves as affected by different carbohydrate sources

From numerous recent studies, it has been demonstrated that the development of the forestomach system in ruminants and thus microbial carbohydrate fermentation do not exclude the potential of the small intestines for enzymatic carbohydrate digestion and subsequent monosaccharide absorption. However, the role of regulatory nutritional factors is still under discussion. Therefore, we investigated the kinetic parameters of intestinal Na⁺‐dependent glucose absorption and SGLT1 expression using isolated brush border membrane vesicles (BBMV) from the jejunum of 10‐week‐old calves kept on either hay, concentrate or corn silage‐based diets in addition to milk replacer. While the maximal transport capacity was significantly higher for concentrate and corn silage‐fed animals, SGLT1 protein expression was highest in BBMV isolated from hay‐fed animals. This observation differs from the prevalent conception that induction of Na⁺‐dependent glucose uptake via SGLT1 is based on an increased number of transporters at the brush border membrane.     

Effect of dietary phytic acid on performance and nutrient uptake in the small intestine of piglets

An experiment was conducted with piglets to determine the effect of dietary phytic acid supplementation on performance, electrophysiological properties of jejunum mounted in Ussing chambers, sodium-dependent glucose transporter 1 (SGLT1) protein expression in jejunum, and plasma glucose and Na concentrations. Sixteen piglets with an average initial BW of 7.40 ± 0.36 kg were randomly assigned to 2 experimental diets with 8 piglets per diet. The diets were casein-cornstarch-based and were either unsupplemented or supplemented with 2% phytic acid (as Na phytate). The basal diet was formulated to meet the recommendation of NRC (1998) for energy, AA, minerals, and vitamins for piglets. The experiment lasted for 21 d, and at the end, BW gain and feed consumption were determined, and blood samples were collected for determination of plasma glucose and Na concentrations. The piglets were then euthanized to determine jejunal electrophysiological properties (transmural potential difference and short-circuit current) and SGLT1 protein expression. Phytic acid supplementation reduced ADG (P = 0.002), ADFI (P = 0.017), and G:F (P = 0.001) from 316.1 to 198.2 g, 437.4 to 360.3 g, and 0.721 to 0.539 g/g, respectively. Phytic acid supplementation also tended to reduce (P = 0.088) potential difference (-3.80 vs. -2.23 mV) and reduced (P = 0.023) short-circuit current from 8.07 to 0.1 μA/cm(2). However, phytic acid supplementation did not affect SGLT1 protein, and blood plasma glucose and Na concentrations. In conclusion, dietary phytic acid reduced growth performance and transmural short-circuit current in the jejunum of piglets. The reduced transmural short-circuit current in the jejunum by phytic acid implies reduced active Na transport in the jejunum by the phytic acid. Therefore, it seems that dietary phytic acid reduces growth performance of pigs partly through reduced capacity of the small intestine to absorb Na.     

Expression of mRNA for sodium-glucose transporter 1 and fatty acid translocase in the ruminant gastrointestinal tract before and after weaning

The mRNA expression of sodium‐glucose transporter 1 (SGLT1) and fatty acid translocase (CD36) in the gastrointestinal tract of Holstein cattle and Saanen goats before and after weaning was investigated. Before weaning, the expression of both SGLT1 and CD36 was highest in the jejunum, relative to the other parts of the gastrointestinal tract in both species. The expression of SGLT1 and CD36 in the duodenum was second highest in the goats. After weaning, SGLT1 and CD36 expression in the small intestine significantly decreased in both species. The expression of both types of transporters was also detected in the forestomach. From these results, it was concluded that the jejunum is probably the major absorption site for glucose and long‐chain fatty acids before weaning, and that the expression of both types of transporters decreases after weaning in cattle and goats.     

Influence of deoxynivalenol on the D-glucose transport across the isolated epithelium of different intestinal segments of laying hens

Deoxynivalenol (DON) decreases glucose absorption in the proximal jejunum of laying hens in vitro and this effect is apparently mediated by the inhibition of the sodium D-glucose co-transporter. DON could modulate the sugar transport of other intestinal regions of chickens. For this purpose, we have measured the effects of DON on the Na(+) D-glucose co-transporter, by addition of DON after and before a glucose addition in the isolated epithelium from chicken duodenum, jejunum, ileum, caecum and colon by using the Ussing chamber technique in the voltage clamp technique. The data showed in all segments of the gut that the addition of D-glucose on the mucosal side produced an increase in the current (Isc) compared with the basal values, the Isc after glucose addition to the small intestine was greater than the Isc of the large intestine compared with the basal values, specially of the jejunum (p < 0.002), indicating that the jejunum is the segment that is the best prepared for Na(+)-D-glucose co-transport. Further addition of 10 microg DON/ml to the mucosal solution decreased the Isc in all segments and the Isc returned to the basal value, especially in the duodenum and mid jejunum (p < 0.05). In contrast, the addition of 5 mmol D-glucose/l on the mucosal side after incubation of the tissues with DON in all segments had no effect on the Isc (p > 0.05), suggesting that DON previously inhibited the Na(+)D-glucose co-transport. The blocking effects of DON in duodenum and jejunum were greater than the other regions of the gut. It can be concluded that the small intestine of laying hens has the most relevant role in the carrier mediated glucose transport and the large intestine, having non-significant capacity to transport sugars, appears to offer a minor contribution to glucose transport because the surface area is small. The effect of D-glucose on the Isc was reversed by DON in all segments, especially in the duodenum and jejunum, suggesting that DON entirely inhibited Na(+)-D-glucose co-transport. This finding indicates that the inhibition of Na(+) co-transport system in all segments could be an important mode of action for DON toxicity of hens.     

Molecular characterisation of carbohydrate digestion and absorption in equine small intestine

Dietary carbohydrates, when digested and absorbed in the small intestine of the horse, provide a substantial fraction of metabolisable energy. However, if levels in diets exceed the capacity of the equine small intestine to digest and absorb them, they reach the hindgut, cause alterations in microbial populations and the metabolite products and predispose the horse to gastrointestinal diseases. We set out to determine, at the molecular level, the mechanisms, properties and the site of expression of carbohydrate digestive and absorptive functions of the equine small intestinal brush-border membrane. We have demonstrated that the disaccharidases sucrase, lactase and maltase are expressed diversely along the length of the intestine and D-glucose is transported across the equine intestinal brush-border membrane by a high affinity, low capacity, Na+/glucose cotransporter type 1 isoform (SGLT1). The highest rate of transport is in duodenum > jejunum > ileum. We have cloned and sequenced the cDNA encoding equine SGLT1 and alignment with SGLT1 of other species indicates 85-89% homology at the nucleotide and 84-87% identity at the amino acid levels. We have shown that there is a good correlation between levels of functional SGLT1 protein and SGLT1 mRNA abundance along the length of the small intestine. This indicates that the major site of glucose absorption in horses maintained on conventional grass-based diets is in the proximal intestine, and the expression of equine intestinal SGLT1 along the proximal to distal axis of the intestine is regulated at the level of mRNA abundance. The data presented in this paper are the first to provide information on the capacity of the equine intestine to digest and absorb soluble carbohydrates and has implications for a better feed management, pharmaceutical intervention and for dietary supplementation in horses following intestinal resection.     

Histomorphology and small intestinal sodium-dependent glucose transporter 1 gene expression in piglets fed phytic acid and phytase-supplemented diets

An experiment was conducted to determine the effect of dietary phytic acid (PA) and phytase supplementation on small intestinal histomorphology and Na-dependent glucose transporter 1 (SGLT1) gene expression in piglets. Twenty-four piglets with an average initial BW of 7.60 ± 0.73 kg were randomly assigned to 3 experimental diets, to give 8 piglets per diet. The diets were a casein-cornstarch-based diet that was supplemented with 0 or 2% PA, or 2% PA (as Na phytate) plus an Escherichia coli-derived phytase at 500 phytase units/kg. The basal diet was formulated to meet the 1998 NRC energy, digestible AA, mineral, and vitamin requirements for piglets. After 10 d of feeding, the piglets were killed to determine small intestinal histomorphology and small intestinal SGLT1 gene expression. Phytic acid supplementation did not affect (P > 0.1) villus height (VH) and the VH-to-crypt depth (CD) ratio, but did decrease (P < 0.05) CD in the jejunum. Phytase supplementation did not affect (P > 0.1) VH, CD, and the VH-to-CD ratio. Phytic acid supplementation reduced SGLT1 gene expression in the duodenum, jejunum, and ileum by 1.1-, 5.4-, and 2.4-fold, respectively. Phytase supplementation increased SGLT1 gene expression in the jejunum by 2.6-fold, but reduced SGLT1 gene expression in the duodenum and ileum by 2.0- and 4.0-fold, respectively. In conclusion, PA reduced CD in the jejunum and SGLT1 gene expression in the duodenum, jejunum, and ileum, whereas phytase supplementation increased the expression of SGLT1 in the jejunum. The reduced SGLT1 gene expression by PA implies that PA reduces nutrient utilization in pigs partly through reduced expression of SGLT1, which is involved in glucose and Na absorption. The increased expression of SGLT1 in the jejunum by phytase supplementation implies that phytase alleviated the negative effects of PA partly through increased expression of SGLT1.     

Influence of abomasal carbohydrates on small intestinal sodium-dependent glucose cotransporter activity and abundance in steers

Most animals adapt readily to increased supplies of carbohydrate in the intestinal lumen by increasing enzymes for degradation and increasing glucose transporter activity. However, the extent of upregulation of Na+-dependent glucose cotransporter 1 (SGLT1) activity and content in response to increased delivery of carbohydrate to the small intestinal lumen of ruminants is unclear. Therefore, an experiment was conducted to determine the effect of glucose and starch hydrolysate on the activity and abundance of SGLT1 in the small intestine of steers. In a randomized complete block design, 40 crossbred beef steers (243+/-2 kg BW) were fed 0.163 Mcal of ME/(kg BW0.75(d; W), 0.215 Mcal of ME/(kg BW0.75 x d; 2M), or 0.163 Mcal ME/(kg BW0.75 x d) and infused for 35 d into the rumen (R) or abomasum (A) with 12.6 g/(kg BW0.75 x d) of starch hydrolysate (S) or into the abomasum with 14.4 g/(kg BW0.75 x d) of glucose (G). Steers were slaughtered, and brush-border membrane vesicles were prepared from the small intestinal samples obtained from five equidistant sites along the intestine. Maltase activity in vesicles and homogenates differed with intestinal sampling site (quadratic, P < 0.001). Steers on the AG treatment yielded a greater intestinal maltase activity (38 nmol glucose x mg protein(-1) x min(-1)) compared with the AS, RS, W, or 2M treatments (34, 26, 23, and 23 nmol glucose x mg protein(-1) x min(-1) respectively [SEM = 3; P = 0.02]). Sodium-dependent glucose uptake averaged 18.4+/-3.94 pmol glucose/(mg protein x s) and was not affected by treatment, but uptake decreased distally along the intestine (P < 0.001). There was no effect of treatment on SGLT1 protein abundance, but SGLT1 protein abundance increased linearly from the duodenum to the ileum (P = 0.05). The inverse relationship between glucose uptake and SGLT1 abundance suggests that the regulation of brush border Na+-dependent glucose transport capacity is complex, involving factors other than the presence of luminal carbohydrate.     

Nonruminant Nutrition Symposium: intestinal glucose sensing and regulation of glucose absorption: implications for swine nutrition

The Na(+/)glucose cotransporter (SGLT1) is the major route for the transport of dietary sugars from the lumen of the intestine into enterocytes. Regulation of this protein is essential for the provision of glucose to the body and avoidance of intestinal malabsorption. This has important nutritional implications in particular for young and growing animals. It has been demonstrated that dietary sugars and artificial sweeteners increase SGLT1 expression and the capacity of the gut to absorb monosaccharides. Furthermore, diets supplemented with artificial sweeteners have been shown to improve growth and performance of weaning piglets. In this review, after describing the organization of intestinal epithelium, the type of gut hormones released in response to dietary carbohydrates, the mechanism underlying the transcellular transport of glucose in the intestine is outlined. Next, a historical background to the work carried out in various laboratories aimed at identifying molecular mechanisms involved in regulation of intestinal glucose transporter, SGLT1, is described. Subsequently, the more recent data on the role of intestinal glucose, or sweet, sensor T1R2 + T1R3, a G protein-coupled receptor, required for upregulation of SGLT1 by dietary sugars and artificial sweeteners, are presented. The glucose sensor subunits, T1R2 + T1R3, are members of the taste receptor family 1, T1R, and are expressed in the gut enteroendocrine cells. Sensing of dietary sugars and artificial sweeteners by T1R2 + T1R3 activates a pathway in endocrine cells leading to secretion of gut hormones. Finally, after describing molecular mechanisms by which a specific gut hormone released by endocrine cells may regulate SGLT1 expression in the neighboring absorptive enterocytes, the application of these findings to enhancing intestinal capacity to absorb dietary sugars in weaning piglets is presented. A better understanding of the molecular events involved in regulation of SGLT1 will allow the identification of nutritional targets with attendant promise of avoiding nutrient malabsorption and enhancing growth and well-being of species.     

Small intestinal starch digestion in steers: effect of various levels of abomasal glucose, corn starch and corn dextrin infusion on small intestinal disappearance and net glucose absorption

Eight Holstein steers (four at 300 kg, four at 406 kg) fitted with an elevated carotid artery, hepatic portal and mesenteric venous catheters, and abomasal and ileal cannulas were used in several 4 x 4 Latin square experiments to evaluate small intestinal starch digestion. They were fed alfalfa hay at 1.5% of BW and abomasally infused with water or glucose, corn starch or corn dextrin (one carbohydrate per Latin square) at 20, 40 or 60 g/h, with subsequent determination of small intestinal disappearance and net portal glucose absorption. Increasing the amount of all three carbohydrates infused abomasally increased the amount of carbohydrate disappearing in the small intestine. Increased infusion of glucose caused a continual increase (linear, P less than .01) in net glucose absorption, whereas net glucose absorption for starch and dextrin was maximal at the 20 g/h infusion (quadratic, P less than .05). With the 60 g/h infusion, 94% of the glucose but only 38% of starch and 29% of small intestinal dextrin disappearance could be accounted for as net glucose absorption, leaving a large portion of starch and dextrin disappearance unaccounted for. Of the infused starch and dextrin passing the ileum, 5.8 and 7.3%, respectively, was unpolymerized glucose, indicating that, at least in the distal small intestine, complete starch hydrolysis exceeded the capacity for glucose disappearance. It is concluded that only about 35% of the raw corn starch disappearing in the steer's small intestine resulted in net portal glucose absorption.     

Effects of B-trichothecenes on luminal glucose transport across the isolated jejunal epithelium of broiler chickens

Trichothecenes are closely-related sesquiterpenoids (ring structure) with a 12, 13 epoxy ring and a variable number of hydroxyl, acetyl or other substituents. In chickens, D-glucose and amino acid absorption occurs via carrier-mediated transport. Recently, it has been observed that deoxynivalenol (DON) alters the gut function and impairs glucose and amino acid transport in chickens. The purpose of this work was to determine the effects of different B-trichothecenes [DON, Nivalenol (NIV), 15-Ac-DON and Fusarenon X (FUS X)] on intestinal carrier-mediated sodium co-transport of D-glucose in the small intestine of broiler chickens. Intestinal transport was determined by changes in the short-circuit current (Isc), proportional to ion transmembrane flux, in the middle segment of the jejunum of broilers with the Ussing chamber technique. D-glucose produced an increase of the Isc, and this effect was reverted by different B-trichothecene mycotoxins, indicating that the glucose induced Isc was altered by B-trichothecenes. The addition of glucose after pre-incubation of the tissues with B-trichothecenes had no effect (p > 0.05) on the Isc, suggesting that B-trichothecenes afflicted the Na(+)-D-glucose co-transport. However, FUX had no obvious effect on the measured parameters. It could be concluded from the present study that the glucose co-transporter activity appears to be more sensitive to DON, NIV and 15-Ac-DON suppression than by FUS X in the jejunum of broilers.     

Influence of the dietary potassium content on transepithelial potassium transport in rat jejunum

In a recent study, we found that the distal rat jejunum is able to secrete K⁺ under in vitro conditions. The question therefore arises as to whether the small intestine might participate in K⁺ homeostasis. Consequently, this study examined the influence of the dietary K⁺ content on transepithelial K⁺ transport in rat jejunum. Rats were fed two diets differing in K⁺ content (control diet 4.0 g K⁺/kg, low K⁺ diet (LK) 0.27 g K⁺/kg). After a minimal feeding period of 7 days, distal jejunal sheets were mounted in Ussing chambers and unidirectional ⁸⁶Rb⁺ fluxes (as a marker for K⁺ transport) were measured under short‐circuit conditions. Jejunum obtained from rats fed the control diet showed a net K⁺ secretion of 200 nmol Rb⁺/h/cm². Unidirectional Rb⁺ fluxes were smaller in distal jejunum from rats fed the LK diet. In these tissues, glucose‐induced short‐circuit current and tissue conductance were also smaller than in controls. However, net Rb⁺ fluxes were not significantly different in small intestine from K⁺‐restricted rats compared with jejunum from control animals. Based on the observation that the dietary K⁺ content does not affect transepithelial net K⁺ transport, we conclude that transcellular K⁺ secretion by the small intestine is not involved in K⁺ homeostasis.     

鸡肠道SGLT1和GLUT2 mRNA表达的组织特异性研究

运用相对定量RT-PCR方法，研究不同肠段Arbor Acre（AA）肉鸡肠道葡萄糖吸收转运主要载体SGLT1和GLUT2mRNA表达的组织特异性。结果发现。随着肠道空间位置的后移，SGLT1 mRNA的表达量逐步降低。十二指肠SGLT1 mRNA的丰度比结直肠高76．19Vo，差异极显著（P〈0．01）；而空肠和回肠SGLT1 mRNA的表达量分别比结直肠高42．86％和38．10％，差异不显著（P〉0．05），但有提高的趋势（P值分别为0．06和0．07）。十二指肠与空肠和回肠相比，SGLTlmRNA的表达量虽然分别高23．33％和27．59％，但差异不显著（P值分别为0．18和0．10）。相对定量分析表明，十二指肠和空肠GLUT2 mRNA丰度非常接近，差异不显著（P〉0．05）。定性研究显示，十二指肠与空肠GLUT2 mRNA丰度高于回肠和结直肠。鸡肠道SGLT1和GLUT2 mRNA表达的组织特异性之生理功能，有待于进一步研究。     

Abundance of intestinal Na+/glucose cotransporter (SGLT1) in roe deer (Capreolus capreolus)

Introduction Based on morphological and physiological differences in their digestive systems H ofmann and S tewart (1972) classified ruminants into three feeding types: concentrate selectors (CS), grass and roughage eaters (GR) and intermediate, opportunistic, mixed feeders (IM). In evolutionary terms CS most closely resemble the original ruminants (H ofmann 1989). They have a relatively small forestomach with large openings between the different parts of the stomach. The retention time of ingesta is short and therefore less suited to optimizing cellulose digestion. They have relatively large saliva glands, producing high volumes of saliva (F ickel et al. 1998), which may facilitate the passage of soluble nutrients down their highly developed ventricular groove. The CS ruminants choose easily digestible forage, especially dicotyledons, which are rich in soluble plant cell contents (PCC, T ixier et al. 1997; D uncan et al. 1998). With evolution, the forestomach of the ruminants became larger relative to body size, and also more subdivided. These evolutionary adaptations optimized the selective retention of feed particles and increased retention time, leading to improvement of cellulose digestion. Large GR are well adapted to digest plant cell walls (PCW), i.e. structural carbohydrates (cellulose); they consequently feed mainly on monocotyledons. Roe deer (Capreolus capreolus) are very small ruminants which select concentrated feed. As energy requirements increase proportional to metabolic body weight (K leiber 1961) roe deer require relatively more energy per unit body mass for maintenance compared to that required by large ruminants (V an S oest 1994; D uncan et al. 1998). Easily digestible forage is not sufficient to satisfy the energy requirements of roe deer. It is proposed therefore that these animals may have other methods of avoiding energy losses due to microbial fermentation, either bypassing nutrients down the ventricular groove (rumen bypass) or by ruminal escape of unfermented and/or partially fermented nutrients (H ofmann 1989). The relatively high content of polyunsaturated fatty acids present in the depot fat of roe deer due to only partial rumen biohydrogenation (M eyer et al. 1998) supports the alternative hypothesis of rumen bypass or ruminal escape. Once reaching the small intestine, partially fermented or bypassed soluble carbohydrates can be further hydrolysed by maltase and sucrase to monosaccharides. These monosaccharides are then available for absorption. The intestinal sodium-dependent glucose cotransporter (SGLT1) in the brush border membrane (BBM) of the enterocytes is a stable indicator for the presence of sugars in the small intestine. The expression and activity of SGLT1 protein are regulated by the level of sugars reaching the small intestine (F erraris and D iamond 1989). Infusion of d -glucose into the intestinal lumen of ruminant sheep for 2 h stimulates the expression of SGLT1 which can be detected 4 days later in the newly formed mature enterocytes (S hirazi -B eechey et al. 1995). When dietary carbohydrate is removed, it takes 3 days before the brush border glucose uptake capacity decreases significantly from control values (F erraris 1994). This reflects the time of physiological cell renewal. In GR, such as sheep, the capacity of the intestine to absorb sugars decreases up to 500-fold during development (S hirazi -B eechey et al. 1995). This decrease in the intestinal absorptive capacity is a reflection of the decline in SGLT1 transport activity and protein abundance. It is not due to modifications in the structure of the absorptive surface and cannot be explained in terms of an age-related process (S hirazi -B eechey et al. 1991). It has been shown that there is a direct correlation between the level of monosaccharides reaching the lumen of the small intestine and the expression of functional SGLT1 protein (D yer et al. 1997). Therefore in this study we aimed to investigate the presence of functional SGLT1 in the small intestine of roe deer as a stable indicator of the availability of glucose in the luminal content of the small intestine. The presence of SGLT1 protein in the small intestine will support the hypothesis of rumen bypass and/or ruminal escape of nutrients. Furthermore we measured the maltase activities in the BBM, as part of the carbohydrates reach the intestinal lumen as polysaccharides and have to be broken down to monosaccharides before absorption.     

Influence of alpha-linked glucose on sodium-glucose cotransport activity along the small intestine in cattle

Thirteen steers (378+/-23 kg) were used in a split-plot experimental design to evaluate the effect of small intestinal carbohydrate on sodium-glucose cotransport in brush border membrane vesicles prepared from five equidistant sites along the small intestine. The steers consumed 7.2+/-0.4 kg/d ground fescue hay and soybean meal-based supplement and were infused ruminally or postruminally with a partial alpha-amylase starch hydrolysate (914.5+/-8.3 g/d) for 7 d. On d 7, five equidistant 1-m small intestinal sections were harvested and frozen in liquid N for later preparation of brush-border membrane vesicles. Maltase activity of the homogenate and vesicle preparations changed (P < 0.001; lowest in the duodenum, highest in the jejunum) and alkaline phosphatase decreased (P < 0.001) along the small intestine. With respect to the original homogenates, the vesicle preparations were enriched 9.80+/-0.83- and 7.64+/-0.67-fold for alkaline phosphatase and maltase, respectively; enrichments were not different between treatments (P = 0.76 and 0.39, respectively). However, alkaline phosphatase and maltase enrichment changed (P < 0.001) along the small intestine. Recoveries of alkaline phosphatase and maltase activities (25.0+/-0.2% and 19.5+/-0.2%, respectively) in the vesicle preparation were not affected (P = 0.29 and 0.21, respectively) by treatment but changed (P < 0.001) along the intestine. Recovery of protein in the vesicle preparation was 2.60+/-0.01% and was not affected by treatment or intestinal site. Sodium-glucose cotransport activity (220+/-44 pmol x mg(-1) x s(-1)) was not affected (P = 0.34) by treatment but did change (P < 0.001; lowest in the ileum, highest in the proximal and mid-jejunum) along the small intestine. Apparent Km of the sodium-glucose cotransporter for glucose was 62.8+/-5.8 microM. The specific activity of maltase was highest in the jejunum, and sodium-glucose cotransport was highest in the first two jejunal sites. However, duodenal maltase activity was lowest and ileal sodium-glucose cotransport activity was lowest. Sodium-glucose cotransport activity may limit small intestinal starch assimilation in the distal small intestine. It does not seem that glucose arising from carbohydrate hydrolysis regulates activity of sodium-dependent glucose transport in cattle.     

Glucose,epithelium, and enteric nervous system: dialogue in the dark

The gastrointestinal epithelium is in close contact with the various components of the chymus, including nutrients, bacteria and toxins. The epithelial barrier has to decide which components are effectively absorbed and which components are extruded. In the small intestine, a nutrient like glucose is mainly absorbed by the sodium linked glucose cotransporter 1 (SGLT1) and the glucose transporter 2 (GLUT2). The expression and activity of both transport proteins is directly linked to the amount of intraluminal glucose. Besides the direct interaction between glucose and the enterocytes, glucose also stimulates different sensory mechanisms within the intestinal wall. The most important types of cells involved in the sensing of intraluminal contents are enteroendocrine cells and neurones of the enteric nervous system. Regarding glucosensing, a distinct type of enteroendocrine cells, the enterochromaffine (EC) cells are involved. Excitation of EC cells by intraluminal glucose results in the release of serotonin (5‐HT), which modulates epithelial functions and activates enteric secretomotorneurones. Enteric neurones are not only activated by 5‐HT, but also directly by glucose. The activation of different cell types and the subsequent crosstalk between these cells may trigger appropriate absorptive and secretory processes within the intestine.     

Influence of fermentable fiber on small intestinal dimensions and transport of glucose and proline in dogs

OBJECTIVE: To determine whether intestinal dimensions and nutrient absorption are influenced by different types of dietary fiber. ANIMALS: 10 adult Beagles of both sexes. PROCEDURE: Dogs were randomly assigned to 2 groups and fed a diet with fermentable fibers (beet pulp and oligofructose) or a nonfermentable fiber (cellulose) for 6 weeks. Effects of the diets on small intestinal dimensions were measured, and transport rates for glucose and proline were determined. Kinetics of glucose and proline uptake were defined in the proximal and middle regions of the small intestine, respectively. RESULTS: Small intestines of dogs fed fermentable fiber had 28% more nominal surface area and 37% more mucosal mass, were 35% heavier, and had 95% higher capacity for carrier-mediated glucose uptake than those of dogs fed a diet with cellulose. Differences were more pronounced in the proximal portion of the intestine. CONCLUSIONS AND CLINICAL RELEVANCE: Diets containing fermentable fibers increase small intestinal dimensions and the capacity for nutrient absorption in dogs. These changes may reduce the risk of enteric infections or aid in treatment of intestinal diseases, particularly those involving reduced nutrient absorption.     

Effects of Cecropin and Synbiotics on the Intestinal Mucosal Morphology and Intestinal Mucosal Immune Cells of AA Broilers

In order to investigate the effects of cecropin and synbiotics on the intestinal mucosal morphology and intestinal mucosal immune cells of AA broilers. 480 of 1-day-old healthy AA broilers were chosen and randomly divided into 4 groups with 4 replicates per group and 30 broilers per replicate. The broilers in group Ⅰ(control group) were fed basal diet,while that in groups Ⅱ to Ⅳ were fed the basal diet supplemented with 0.5% cecropin,0.3% synbiotics,0.5% cecropin+0.3% synbiotics,respectively. The trial lasted for 42 days. The result showed that compared with group Ⅰ,the villus height of duodenum and ileum in group Ⅳ were extremely significantly increased (P<0.01).The crypt depth of jejunum and ileum in group Ⅱ,and that of small intestine in group Ⅲ were significantly or extremely significantly decreased (P<0.05;P<0.01).The villus height/crypt depth of small intestine in groups Ⅱ and Ⅲ,and that of duodenum and ileum in group Ⅳ were significantly or extremely significantly increased (P<0.05;P<0.01).The villus width of jejunum in group Ⅱ was significantly decreased (P<0.05),while the villus width of duodenum and jejunum in group Ⅲ,that of jejunum and ileum in group Ⅳ were extremely significantly decreased (P<0.01).The mucous thickness of jejunum in groups Ⅱ and Ⅲ were significantly increased (P<0.05),while that of small intestine in group Ⅳ was extremely significantly increased (P<0.01).The number of the intraepithelial lymphocyte of ileum in group Ⅱ was significantly increased (P<0.05),and that of duodenum in group Ⅲ and small intestine in group Ⅳ were extremely significantly increased (P<0.01).The number of the goblet cell of duodenum in group Ⅲ,duodenum and ileum in group Ⅳ were extremely significantly increased (P<0.01).The mast cell of jejunum in group Ⅳ was significantly increased (P<0.05).In conclusion,both the cecropin and synbiotics could improve the small intestine mucosal structure and promote the small intestine mucosal immunocompetent cells proliferation in AA broiler, and the effect of combined utilization would be better.     

天蚕素和合生素对AA肉鸡小肠黏膜形态和小肠免疫细胞的影响

为研究日粮中添加天蚕素、合生素对AA肉鸡小肠黏膜形态及免疫细胞的影响,试验选用480只1日龄健康AA肉鸡,随机分为4组,每组4个重复,每个重复30只鸡。对照组（Ⅰ组）饲喂基础日粮,试验组（Ⅱ~Ⅳ组）分别在基础日粮中添加0.5%天蚕素、0.3%合生素、0.5%天蚕素+0.3%合生素。试验期42 d。结果显示,与Ⅰ组相比,Ⅳ组十二指肠、回肠绒毛高度极显著升高（P<0.01）;Ⅱ组空肠和回肠、Ⅲ组小肠各段隐窝深度显著或极显著降低（P<0.05;P<0.01）;Ⅱ、Ⅲ组小肠各段和Ⅳ组十二指肠、回肠绒毛高度/隐窝深度显著或极显著升高（P<0.05;P<0.01）;Ⅱ组空肠绒毛宽度显著降低（P<0.05）,Ⅲ组十二指肠和空肠、Ⅳ组空肠和回肠绒毛宽度均极显著降低（P<0.01）;Ⅱ、Ⅲ组空肠黏膜厚度显著升高（P<0.05）,Ⅳ组小肠各段黏膜厚度均极显著升高（P<0.01）。Ⅱ组回肠上皮内淋巴细胞数量显著升高（P<0.05）,Ⅲ组十二指肠、Ⅳ组小肠各段上皮内淋巴细胞数量极显著升高（P<0.01）;Ⅲ组十二指肠、Ⅳ组十二指肠和回肠杯状细胞数量极显著升高（P<0.01）;Ⅳ组空肠肥大细胞数量显著升高（P<0.05）。综上所述,天蚕素、合生素单独或联合添加均能改善AA肉鸡小肠黏膜结构,促进小肠黏膜免疫细胞增殖,联合添加效果最佳。