Glucose metabolism in proliferating epithelial cells from the rat colon.

1. The effects of fasting and fasting followed by refeeding on the activities of the oxidative pentose pathway (OPP) and the tricarboxylic acid cycle (TCA) in isolated rat colonocytes were estimated by the rate of production of 14CO2 from [1-14C]glucose and [6-14C]glucose, respectively. 2. Refeeding after a fast induced a 2-3-fold increase in glucose flux through the OPP and TCA cycle and the degree of change was similar in colonocytes from the proximal and distal colon. 3. Butyrate at a concentration of 40 mM inhibited the OPP by 20-30% (P less than 0.05) but had no effect on the activity of the TCA cycle. Glutamine at a concentration of 2 mM decreased the glucose flux through both the OPP and the TCA cycle by 30-50% (P less than 0.05). 4. Production of 14CO2 from the oxidation of butyrate or glucose indicated that the former was 5-7 times more active in colonocytes from fasted rats. After refeeding, however, butyrate utilization was similar to fasting values in the proximal colon but significantly lower (P less than 0.05) in the distal colon.     

Consumption of carbohydrates, amino acids and oxygen across the intestinal circulation in the fetal sheep

Since large volumes of nutrient rich amniotic fluid are swallowed by the fetus, it has been suggested that intestinal digestion and absorption contribute significantly to fetal nutrition. To see if nutrients are being gained across the intestine, we measured blood flow and intestinal arteriovenous concentration differences of glucose, alpha-amino nitrogen, lactate, fructose and oxygen in eleven third trimester fetal sheep with chronically implanted vascular catheters. We found that in fetal blood circulating through the intestine nutrient concentration decreased significantly with arterio-venous concentration differences for glucose of 0.78 +/- 0.21 (SEM) mg/dl (P < 0.002), for alpha-amino nitrogen of 0.52 +/- 0.15 mg/dl (P < 0.005), for lactate of 0.68 +/- 0.24 mg/dl (P < 0.05) and for oxygen of 1.50 +/- 0.08 ml/dl (P < 0.001). Fructose concentration did not change. Blood flow to the fetal intestine averaged 89.92 +/- 7.16 ml/min and the intestine consumed 0.74 +/- 0.24 mg of glucose, 0.43 +/- 0.17 mg of alpha-amino nitrogen, 0.83 +/- 0.28 mg of lactate and 1.37 +/- 0.14 ml of oxygen per minute. Compared to previously published values for the umbilical uptake of nutrients the fetal intestine metabolizes about 4% of the glucose, 6% of the alpha-amino nitrogen, 13% of the lactate and 6% of the oxygen obtained across the umbilical circulation. Intestinal absorption does not appear to serve as a source of simple nutrients for the rest of the fetus, in fact intestinal metabolism extracts significant amounts of nutrients from fetal blood.     

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.     

Influence of nitrate and nitrite on electrolyte transport by the rat small and large intestine

1. The influence of nitrate and nitrite on net absorption of electrolytes (Na+, K+, Cl-) and water from ligated loops was studied at various intestinal sites in rats. 2. Nitrate strikingly reduced Cl- absorption in rat proximal and distal colon, whereas Na+ absorption was reduced only moderately. Nitrite also reduced Cl- absorption in the colon. 3. Nitrate showed no significant effect on electrolyte absorption in the small intestine. 4. The results suggest that Cl-/HCO3- on exchange is the major route of Cl- absorption in the colon, whereas this mechanism seems not to be of importance for Cl- absorption by the small intestine.     

Gastrointestinal absorption of estrone sulfate in germfree and conventional rats

Steroids are extensively excreted in the bile of rats. There was no significant difference in biliary excretion of steroid following administration of [3H]-estrone sulfate into the proximal small intestine (PSI) of conventional (CVL; 17.8 +/- 62%; mean +/- SD) or germfree (GF; 28.2 +/- 5.3) rats. A similar finding resulted from administration into the distal small intestine (DSI)-CVL, 22.3 +/- 11.8%; GF, 11.4 +/- 3.7%. However, when the drug was given into the caecum, excretion in the bile of CVL rats after 5 h was 59.1% whereas in GF rats it was only 1.7%. When estrone was injected into the PSI and DSI of CVL and GF rats, absorption (as judged by excretion in bile) was more rapid than that seen with estrone sulfate. Five hours after injection into the PSI, biliary excretion was, in CVL 88.2% and in GF 81.7% and after injection into the DSI excretion was, in CVL 84.7% and in GF 83.6%. Absorption of estrone from the caeca of GF rats was apparently reduced (49.0% and 25.3% excreted in the bile of CVL and GF rats respectively). There was no significant difference in bile flow rate between CVL and GF rats. These results give unequivocal evidence of intact absorption of estrone sulfate from the small intestine of the rat. The rate of absorption is however very much reduced compared to the non-sulphated steroid. Estrone sulfate is not absorbed intact in the caecum but is hydrolysed by the gut microflora prior to absorption.     

Changes in Carboxypeptidase A,Dipeptidase and Na<Superscript>+</Superscript>/K<Superscript>+</Superscript> ATPase Activities in the Intestine of Rats Orally Exposed to Different Doses of Cadmium

The purpose of the present study was to evaluate the effect of cadmium on some protein digestive and absorption enzymes in rats. Thirty-six rats were grouped into three groups of 12 animals each; one group received deionised water and acted as control. One group received 445 μM Cd and the last group received 890 μM Cd in their drinking water for a period of one month. The results obtained indicate that increasing the level of cadmium from 445 μM to 890 μM in the drinking water of the rats led to 29 and 23 increase in accumulated cadmium in the proximal and distal small intestine respectively. The body weight gain of rats exposed to 445 μM and 890 μMCd was decreased by about 24 and 43 respectively when compared with the control. The activities of carboxypeptidase A, dipeptidase and Na+/K+ ATPase were reduced in the mucosa of the proximal end of the small intestine of cadmium exposed rats. The reduction was dose dependent; with the 890 μM Cd exposed rats displaying the least activities. In the distal small intestine, the activities of these enzymes were restored in the 445 μM Cd exposed rats to levels that were not statistically different (P>0.05) from those observed in the controls. In the 890 μMCd exposed rats, dipeptidase activity improved by about 80 compared with the activity of the enzyme in the proximal small intestine. Likewise, Na+/K+ ATPase activity increased by about 125 compared with the observed level in the proximal small intestine. The study suggests that cadmium given to rats in drinking water compromise protein digestion and absorption of nutrients particularly in the proximal region of small intestine and could account for weight reduction associated with cadmium toxicity. Published online December 2004     

禁食和重喂食对大绒鼠消化道长度与重量的影响

为探讨禁食和重喂食对栖息于横断山地区大绒鼠(Eothenomys miletus)消化道形态的影响,对禁食和重喂食条件下大绒鼠消化道各项指标进行了测定.实验分别测定了大绒鼠禁食12h、24 h、36 h和重喂食12 h、48 h、7d后的总消化道、胃、小肠、大肠、盲肠的长度及其含内容物重、去内容物重、干重.结果表明:禁食后,总消化道含内容物重、胃含内容物重和胃去内容物重增加,重喂食7d后均恢复到对照组水平.小肠含内容物重在禁食12h时最大,在重喂食12h时最小,重喂食48 h后恢复到对照组水平.禁食和重喂食条件下,大绒鼠的大肠和盲肠各指标均没有显著变化.以上结果表明,大绒鼠在食物受到限制、饥饿等胁迫因子作用下,可能通过调节消化道形态来满足部分能量需求,维持正常的生理机能.大绒鼠的消化道在禁食和重喂食中表现出的变化模式,可能与其食物资源时常波动的野外生存环境有关,从一方面反映了该物种在食物胁迫下的生存机制和适应对策.     

Intestinal absorption of copper: effect of sodium

The mechanisms of copper (Cu) absorption from the small intestinal lumen are poorly understood. In this study we investigated the role of sodium (Na) during the removal of Cu from the lumen of jejunal and ileal segments, using an in situ perfusion procedure in the anesthetized rat. Intestinal absorption of Cu from a 31 microM solution was highest in the presence of an isotonic concentration of NaCl, as compared to solutions containing either glycerol (GRL) or N-methyl-D-glucamine (NMG) as osmotic agents. In the jejunum, mean +/- SEM Cu absorption rates in the presence of the following solutes were: with NaCl, 57.5 +/- 10.5 pmole/min X cm; with GRL, 13.3 +/- 14.7 (P less than 0.05); with NMG, 18.4 +/- 10.1 (P less than 0.05). In the ileum, copper absorption in the presence of NaCl was 64.4 +/- 9.6; with GRL, 24.3 +/- 10.1 (P less than 0.01); with NMG, 15.8 +/- 3.7 (P less than 0.001). Kinetic analysis of the carrier-mediated component of Cu absorption in rat jejunum yielded a Vmax = 47.5 pmole/min X cm and an apparent Kt = 21 microM. The diffusion coefficient was calculated to be 1.4 X 10(-5) cm2/sec. The absorption of Cu was independent of net water absorption, which was highest in the presence of GRL and abolished and reversed into secretion by NMG. The data obtained are indicative of a significant role of Na in the small intestinal transport of Cu, in vivo, although not directly related to unidirectional water fluxes. The cation specificity of Na in this process remains to be elucidated, although the results support earlier studies which postulated that mediated transport may constitute a major component of Cu absorption in the mammalian small intestine.     

Insulin, cGMP, and TGF-beta signals regulate food intake and quiescence in C. elegans: a model for satiety

Despite the prevalence of obesity and its related diseases, the signaling pathways for appetite control and satiety are not clearly understood. Here we report C. elegans quiescence behavior, a cessation of food intake and movement that is possibly a result of satiety. C. elegans quiescence shares several characteristics of satiety in mammals. It is induced by high-quality food, it requires nutritional signals from the intestine, and it depends on prior feeding history: fasting enhances quiescence after refeeding. During refeeding after fasting, quiescence is evoked, causing gradual inhibition of food intake and movement, mimicking the behavioral sequence of satiety in mammals. Based on these similarities, we propose that quiescence results from satiety. This hypothesized satiety-induced quiescence is regulated by peptide signals such as insulin and TGF-beta. The EGL-4 cGMP-dependent protein kinase functions downstream of insulin and TGF-beta in sensory neurons including ASI to control quiescence in response to food intake.     

Soybean impairs Na(+)-dependent glucose absorption and Cl- secretion in porcine small intestine

Recent evidence indicates that soybean, which is widely used in animal nutrition, could directly alter intestinal ion and nutrient transport. However, the mechanisms involved are still unknown. The aim of the study was to investigate the effect of three differently treated soybean products on the glucose and Cl- transport capacity in porcine small intestine by the Ussing chamber technique. Jejunal and ileal piglet epithelial tissues were pre-incubated with extracts of raw soybean flour (RSF), heated soybean flour (HSF), or ethanol heat-treated soybean protein concentrate (SPC). The Na(+)-dependent glucose co-absorption capacity was then measured as an increase in the short-circuit current (ISC) after luminal addition of D-glucose. The effect of the soybean products on cAMP-dependent Cl- secretion was measured as the increase in ISC after the addition of the phosphodiesterase inhibitor, theophylline, while nervous regulation of Cl- secretion was investigated by the addition of the enteric neurotransmitters; 5-hydroxytryptamine (5-HT), substance P and vasoactive intestinal polypeptide (VIP). Incubation with RSF and HSF induced a 30% decrease of the Na(+)-dependent glucose absorption capacity in the jejunum. The effect was similar for RSF in the ileum. Theophylline-induced secretion was decreased by 30% after incubation with RSF, HSF and SPC but only in the jejunum. 5-HT-, substance P- and VIP-induced secretion were not altered by incubation with soybean extracts except in the HSF-incubated where the substance P-induced secretion was significantly reduced. In conclusion, soybean contains ethanol-sensitive heat-insensitive compounds impairing Na(+)-dependent glucose absorption in the jejunum and ileum, and ethanol- and heat-insensitive compounds causing an acute impairment of cAMP-dependent jejunal secretion.     

Somatostatin content and binding in small intestinal mucosa from fed, fasted, and refed rabbits

The present study is an investigation of the effects of 12- to 96-hours' starvation and 96-hours' starvation plus 48-hours' refeeding on both somatostatin-like immunoreactivity (SLI) and cytosolic somatostatin binding sites in rabbit small intestinal mucosa. The SLI concentration increased after 24 h in duodenal and jejunal mucosa, but not in ileal mucosa, and reached its highest value after 96 h of fasting. The number of specific high and low-affinity somatostatin binding sites, but not their affinity, decreased with the duration of fasting in the same gut segments, refeeding of fasted animals resulted in a return to normal control values for small intestine mucosal SLI and somatostatin binding.     

Glucagon-like peptide 2 has limited efficacy to increase nutrient absorption in fetal and preterm pigs

Exogenous glucagon-like peptide 2 (GLP-2) prevents intestinal atrophy and increases nutrient absorption in term newborn pigs receiving total parenteral nutrition (TPN). We tested the hypothesis that the immature intestine of fetuses and preterm neonates has a diminished nutrient absorption response to exogenous GLP-2. This was accomplished using catheterized fetal pigs infused for 6 days (87-91% of gestation) with GLP-2 (25 nmol.kg(-1).day(-1) iv; n = 7) or saline (n = 7), and cesarean-delivered preterm pigs (92% of gestation) that received TPN with GLP-2 (25 nmol.kg(-1).day(-1) iv; n = 8) or saline (n = 7) for 6 days after birth. Responses to GLP-2 were assessed by measuring intestinal dimensions, absorption of nutrients (glucose, leucine, lysine, proline) by intact tissues and brush border membrane vesicles, and abundance of sodium-glucose cotransporter mRNA. Infusion of GLP-2 increased circulating GLP-2 levels in fetuses, but did not increase intestinal mass or absorption of nutrients by intact tissues and brush border membrane vesicles, except for lysine. Administration of exogenous GLP-2 to preterm TPN-fed pigs similarly did not increase rates of nutrient absorption, yet nutrient absorption capacities of the entire small intestine tended to increase (+10-20%, P < 0.10) compared with TPN alone due to increased intestinal mass (+30%, P < 0.05). GLP-2 infusion did not increase sodium-glucose cotransporter-1 mRNA abundance in fetuses or postnatal preterm pigs. Hence, the efficacy of exogenous GLP-2 to improve nutrient absorption by the intestine of fetal and preterm pigs is limited compared with term pigs and more mature animals and humans.     

Electroneutral sodium absorption and electrogenic anion secretion across murine small intestine are regulated in parallel

Electrolyte transport processes of small intestinal epithelia maintain a balance between hydration of the luminal contents and systemic fluid homeostasis. Under basal conditions, electroneutral Na(+) absorption mediated by Na(+)/H(+) exchanger 3 (NHE3) predominates; under stimulated conditions, increased anion secretion mediated by CFTR occurs concurrently with inhibition of Na(+) absorption. Homeostatic adjustments to diseases that chronically affect the activity of one transporter (e.g., cystic fibrosis) may include adaptations in the opposing transport process to prevent enterosystemic fluid imbalance. To test this hypothesis, we measured electrogenic anion secretion (indexed by the short-circuit current) across NHE3-null [NHE3(-)] murine small intestine and electroneutral Na(+) absorption (by radioisotopic flux analysis) across small intestine of mice with gene-targeted disruptions of the anion secretory pathway, i.e., CFTR-null [CFTR(-)] or Na(+)-K(+)-2Cl(-) cotransporter-null [NKCC1(-)]. Protein expression of NHE3 and CFTR in the intestinal epithelia was measured by immunoblotting. In NHE3(-), compared with wild-type small intestine, maximal and bumetanide-sensitive anion secretion following cAMP stimulation was significantly reduced, and there was a corresponding decrease in CFTR protein expression. In CFTR(-) and NKCC1(-) intestine, Na(+) absorption was significantly reduced compared with wild-type. NHE3 protein expression was decreased in the CFTR(-) intestine but was unchanged in the NKCC1(-) intestine, indicating that factors independent of expression also downregulate NHE3 activity. Together, these data support the concept that absorptive and secretory processes determining NaCl and water movement across the intestinal epithelium are regulated in parallel to maintain balance between the systemic fluid volume and hydration of the luminal contents.     

Dietary induction of angiotensin-converting enzyme in proximal and distal rat small intestine

Induction of angiotensin-converting enzyme was examined in proximal and distal intestinal segments of rats fed a low-protein (4%) diet and then switched to a high-protein (gelatin) diet. Animals were killed at varying time points, and brush-border membranes and total RNA were prepared from the segments. In the proximal intestine, there was a fivefold increase in angiotensin-converting enzyme levels after 14 days but only a twofold change in mRNA. In the distal intestine, there was no increase in enzyme activity but mRNA increased 2.4-fold. Organ culture was used to measure changes in enzyme biosynthesis. There was a 5- to 6-fold increase in the biosynthesis of angiotensin-converting enzyme in the proximal intestine 24 h after the switch to the gelatin diet and a 1.6-fold increase in mRNA levels. No change in biosynthesis was observed in the distal small intestine despite an increase in mRNA. These results support the conclusion that rapid dietary induction of intestinal angiotensin-converting enzyme is differentially regulated in proximal and distal segments of the small intestine.     

Distribution of estrone sulfatase activity in the intestine of germfree and conventional rats

The intestinal content, the mucosa and the rest of the intestinal wall of germfree (GF) and conventional ( CVL ) rats were tested for in vitro hydrolysis of [3H]estrone sulfate. In homogenates from GF rat intestine some estrone sulfate hydrolysis was detected in those from the proximal small intestine (PSI) (4.2 +/- 0.1% hydrolyzed after 4 h), but not in those from the distal small intestine (DSI) and the caecum. Estrone sulfate was also hydrolyzed by the homogenates of the mucosa and the rest of the intestinal wall from each of the segments tested (PSI: 12.8 +/- 0.4% (mucosa) and 21.5 +/- 2.1 (wall); DSI: 8.2 +/- 0.9% (mucosa) and 17.3 +/- 1.7% (wall); caecum: 8.8 +/- 1.6% (mucosa) and 17.3 +/- 0.5% (wall) ). In the homogenates of CVL rat intestine, the estrone sulfatase activity in the rest of the intestinal wall did not differ considerably from the values for GF rats, when expressed per mg protein of the homogenate. The mucosa of the CVL rats, however, showed higher rates of hydrolysis than the mucosa of the GF rats. The microbial estrone sulfatase activity in the intestinal content of CVL rats, tested by anaerobic incubation, was high in the caecum (91.7 +/- 6.6% after 4 h), but very low in the PSI (2.2 +/- 0.7%) and DSI (1.3 +/- 0.5%). Serial dilutions of the caecal content also showed higher viable numbers of estrone sulfate hydrolyzing bacteria. These results add further weight to the suggestion that estrone sulfate may be absorbed from the small intestine, but has to be hydrolyzed in the caecum by the gut microflora prior to absorption.     

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.     

5-(N,N-Dimethyl)-amiloride to discriminate the Unidirectional electrolyte transports in rat small intestine and proximal colon in vivo

The effect of dimethyl-amiloride (DMA), a selective Na+/H+ exchange blocker, was studied on electrolyte net fluxes and unidirectional fluxes of Na and Cl at four levels of rat intestine in vivo in basal conditions. DMA was applied intraluminally at concentrations of 10(-4) and 10(-3) M in the model of ligated loops prepared from duodenum, proximal jejunum, distal ileum and ascending colon in fasted Sprague Dawley rats. Two iso-osmotic test solutions were used: (1) hypo-ionic: Na+ 80 mM and (2) iso-ionic: Na+ 148 mM, pH 8.2. 22Na was placed in the loop and 36Cl was given by intravenous route at the beginning of the experiment. Na+/H+ was calculated by two different means, one was based on pH variation following amiloride inhibition of Na influx, the other on the calculation of the passive Na transport. The quantitative evaluation shows that Na/H exchange largely contributes to the electroneutral absorption and luminal pH regulation. The exchanger activity decreases from duodenum, jejunum, ileum and colon where it is completed by K/H exchange to assure low colon luminal pH.     

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.     

The Hepatic Genes for Immunoproteasome Are Upregulated by Refeeding after Fasting in the Rat

Considering that animals maintain energy homeostasis in response to nutrient levels, experiments were done to elucidate the temporal effects of refeeding after fasting on gene expression profiles in the rat liver. Using DNA microarray technology, we first compared gene expression profiles in the livers of rats allowed to feed for 6 h after fasting for 18 h and those in 24-h fasting rats, and found that the expression levels of energy metabolism-related genes in the two groups were different. In addition, refeeding induced upregulation of the genes encoding immunoproteasome components. Finally, immunoblot analysis confirmed changes in protein levels, suggesting that refeeding after fasting enhanced immune function.