Absorption Of D-glucose Research Articles

Antihyperglycemic potential of the Lavandula stoechas aqueous extract via inhibition of digestive enzymes and reduction of intestinal glucose absorption

BackgroundDiabetes mellitus is a widespread metabolic disorder affecting global populations. Lavandula stoechas from Moroccan traditional medicine is used for its potential anti-diabetic effects. ObjectiveThis study aims to evaluate the antihyperglycemic impact of the aqueous extract of L. stoechas (AqLs) and explore its mechanisms. MethodsThe study employed a glucose tolerance test (OGTT) on normal and diabetic Wistar rats, administering AqLs at 150 mg/kg. In vitro, AqLs was tested against α-glucosidase and α-amylase activities, confirmed in vivo using normal and Allx-diabetic rats. The extract’s impact on intestinal d-glucose absorption was assessed using the jejunum segment perfusion technique at 250 mg/kg in situ. Albino mice were used to assess toxicity. ResultsAqLs significantly reduced postprandial hyperglycemia (P < 0.001) due to glucose overload. It inhibited pancreatic α-amylase (IC50: 0.485 mg/mL) and intestinal α-glucosidase (IC50: 168 µg/mL) in vitro. Oral AqLs at 150 mg/kg reduced hyperglycemia induced by sucrose and starch in normal and diabetic rats. It also lowered (P < 0.001) intestinal glucose absorption in situ at 250 mg/kg. Oral acute toxicity tests on Albino mice indicated no adverse effects at different doses. Conclusionto summarize, L. stoechas has evident antihyperglycemic effects attributed to inhibiting intestinal glucose absorption and key monosaccharide digestion enzymes like α-amylase and α-glucosidase.

Antioxidant Activity and Inhibition of Carbohydrate Digestive Enzymes Activities of Artemisia campestris L.

Carbohydrate digestive enzymes play a major role in the management of the postprandial hyperglycemia. A chronic hyperglycemia can lead to serious health problems due to excessive production of several reactive oxygen species. Therefore, the inhibition of carbohydrate digestive enzyme and the use of antioxidant natural product can be an important strategy to control the glycaemia level and prevent against the complication of diabetes. The study aims to perform a phytochemical analysis, antioxidant activity, inhibitory effect on α -amylase, α -glucosidase (in vitro and in vivo) and the intestinal glucose absorption in Wistar rats of Artemisia campestris aqueous extract (AcAE) and hydro-ethanolic extract (AcEE). The test of total phenolic content, show that the AcAE has the highest quantity of polyphenol (44.65 ± 0.54 μ g GAE/mg extract) compared to the AcEE (31.7 ± 0.53 μ g GAE/mg extract) significantly. The amount of flavonoid and condensed tannins content in AcAE is 24.41 ± 3.57 μ g QrE/mg extract, 14.31 ± 5.26 μ g CE/mg respectively. The AcAE has also exhibit a great antioxidant activity in DPPH-scavenging and Ferric reducing antioxidant power assay (FRAP) compared to AcEE with an IC 50 = 0.355 ± 0.057 mg/mL and IC 50 = 0.269 ± 0.025 mg/mL. However, in a β -carotene bleaching assay the AcEE has the highest effect with an IC 50 = 0.319 ± 0.097 mg/mL. The both extract of Artemisia campestris L. (250 mg/kg) decreased postprandial hyperglycemia in the normal and alloxane diabetic rats in a very significant manner after starch or sucrose administration as an α -amylase and α -glucosidase substrate respectively. This result is confirmed in vitro by a remarkable inhibitory effect on α -amylase digestive enzymes by an IC 50 = 1.259 ± 0.128 mg/mL and IC 50 = 0.602 ± 0.072 mg/mL receptively for AcAE and AcEE. For the α -glucosidase enzyme, the both extracts significantly inhibit α -glucosidase activity compared to the control and they are almost similar to each other. Using a jejunum perfusion technique (in situ), Artemisia campestris L. decrease the intestinal D-glucose absorption activity significantly compared to the control and comparable to the Phlorizin used as a positive control by an amount of glucose absorbed equal a 6.53 ± 0.57, 5.34 ± 0.64 and 4.71 ± 0.24 mg/10 cm/h, for AcAE, AcEE and Phlorizin respectively. These results showed that the Artemisia campestris L. has highest phenolic content, antioxidant activity and demonstrated a postprandial anti-hyperglycemic effect via the inhibiting of the carbohydrate digestive enzyme ( α -amylase and α -glucosidase) and the intestinal glucose absorption.

Inhibition of α-Amylase, α-Glucosidase, and Lipase, Intestinal Glucose Absorption, and Antidiabetic Properties by Extracts of Erodium guttatum.

Erodium guttatum is widely used in traditional medicine to treat various diseases, including diabetes. In this study, we evaluated in vitro inhibitory activity of extracts of E. guttatum on α-amylase, α-glucosidase, and lipase and then studied in vivo using different animal models. The results showed that the aqueous and alcoholic extracts of E. guttatum significantly inhibited digestive enzymes. The extracts of E. guttatum significantly reduced postprandial hyperglycemia after starch loading in normal rats. Additionally, extracts of E. guttatum significantly decrease the intestinal absorption of D-glucose. However, the methanolic extract of E. guttatum showed remarkable antidiabetic activity compared to the aqueous and ethanolic extracts of E. guttatum. In addition, the extracts significantly reduced blood sugar levels in albino mice and hematological and biochemical profiles. Therefore, the results of this study show that the extracts of E. guttatum have antidiabetic effects and could therefore be suggested in the management of type 2 diabetes.

Ammodaucus leucotrichus Coss. &amp; Durieu: Antihyperglycemic activity via the inhibition of α-amylase, α-glucosidase, and intestinal glucose absorption activities and its chemical composition

Context: Ammodaucus leucotrichus commonly known as a ‘Kamune es sufi or akâman’ in Morocco, is used to treat many diseases including diabetes. Aims: To investigate the antihyperglycemic activity of an aqueous extract of fruits A. leucotrichus (AEAL) and its chemical composition. Methods: The antihyperglycemic effect of the AEAL was tested against intestinal α-glucosidase and pancreatic α-amylase activities, in vitro, at the concentrations (41-328 µg/mL) and (0.5-3 mg/mL) respectively. In addition, the inhibitory effect of the AEAL (150 mg/kg) against these enzymes was confirmed, in vivo in normal and alloxan diabetic rats using sucrose, starch, and glucose as a substrate.The antihyperglycemic effect of the AEAL was also tested against intestinal D-glucose absorption activity at the dose of 150 mg/kg using the jejunum segment perfusion technique, in situ. Chemical composition was evaluated using HPLC. Results: The results of this study showed that the AEAL was significantly (p&lt;0.001) inhibited the intestinal α-glucosidase, in vitro (IC50 = 0.254 mg/mL). The same effect of this extract was confirmed against the pancreatic α-amylase activity, with IC50 = 1.81 mg/mL. In vivo, the oral intake of the AEAL at a dose of 150 mg/kg was significantly attenuated the hyperglycemia induced by the sucrose, starch, and glucose in the normal and alloxan diabetic rats. AEAL, also, significantly (p&lt;0.01) decreased intestinal glucose absorption, in situ.HPLC results revealed the presence of four molecules: vanillin, quercetin, kaempferol, and thymol. Conclusions: A. leucotrichus showed a significant antihyperglycemic activity. This effect can be explained by the inhibition of α-amylase, α-glucosidase activities, and the intestinal absorption of D-glucose.

Opuntia dillenii (Ker Gawl.) Haw., Seeds Oil Antidiabetic Potential Using In Vivo, In Vitro, In Situ, and Ex Vivo Approaches to Reveal Its Underlying Mechanism of Action.

Opuntia dillenii Ker Gawl. is one of the medicinal plants used for the prevention and treatment of diabetes mellitus (DM) in Morocco. This study aims to investigate the antihyperglycemic effect of Opuntia dillenii seed oil (ODSO), its mechanism of action, and any hypoglycemic risk and toxic effects. The antihyperglycemic effect was assessed using the OGTT test in normal and streptozotocin (STZ)-diabetic rats. The mechanisms of action were explored by studying the effect of ODSO on the intestinal absorption of d-glucose using the intestinal in situ single-pass perfusion technique. An Ussing chamber was used to explore the effects of ODSO on intestinal sodium-glucose cotransporter 1 (SGLT1). Additionally, ODSO’s effect on carbohydrate degrading enzymes, pancreatic α-amylase, and intestinal α-glucosidase was evaluated in vitro and in vivo using STZ-diabetic rats. The acute toxicity test on mice was performed, along with a single-dose hypoglycemic effect test. The results showed that ODSO significantly attenuated the postprandial hyperglycemia in normal and STZ-diabetic rats. Indeed, ODSO significantly decreased the intestinal d-glucose absorption in situ. The ex vivo test (Ussing chamber) showed that the ODSO significantly blocks the SGLT1 (IC50 = 60.24 µg/mL). Moreover, ODSO indu\\ced a significant inhibition of intestinal α-glucosidase (IC50 = 278 ± 0.01 µg/mL) and pancreatic α-amylase (IC50 = 0.81 ± 0.09 mg/mL) in vitro. A significant decrease of postprandial hyperglycemia was observed in sucrose/starch-loaded normal and STZ-diabetic ODSO-treated rats. On the other hand, ODSO had no risk of hypoglycemia on the basal glucose levels in normal rats. Therefore, no toxic effect was observed in ODSO-treated mice up to 7 mL/kg. The results of this study suggest that ODSO could be suitable as an antidiabetic functional food.

Inhibitory effect of roasted/ unroasted Argania spinosa seeds oil on α- glucosidase, α-amylase and intestinal glucose absorption activities

BackgroundDiabetes mellitus is a serious metabolic disease, which affects a large number of populations in the world. Phytotherapy is considered as the most remedies used by Moroccan people to treat this pathology. Argania spinosa L. (SKEELS) seeds oils is among the products that are used traditionally in Morocco for the anti-diabetic purposes. ObjectiveThe aim of this study is to investigate the effect of roasted (Roil) and unroasted (UnRoil) Argan seeds oils on α-glucosidase, α-amylase and intestinal glucose absorption activities in vitro and in vivo. MethodsThe antihyperglycemic effect of the roasted and unroasted Argania spinosa L. seeds oils was tested against α-glucosidase and α-amylase activities, in vitro, at the concentrations (82, 165, 328 and 656 µg/mL) and (0.9, 2.25, 4.5 and 9 mg/mL) respectively. In addition, the inhibitory effect of the oils against these enzymes was confirmed, in vivo, in normal and STZ- diabetic rats. The antihyperglycemic effect of these oils was also tested against intestinal d-glucose absorption activity at the dose of 1 mL/Kg using the jejunum segment perfusion technique, in situ. ResultsThe results of this study were showed that the Roil and the UnRoil were significantly (p < 0.001) inhibited the pancreatic α-amylase, in vitro, with (IC50 = 23, 98 mg/mL) and (IC50 = 5, 87 mg/mL) respectively. The same effect of these oils was confirmed against the intestinal α-glucosidase activity, with (IC50 = 0.081 mg/mL) and (IC50 = 0.117 mg/mL) for UnRoil and Roil respectively. Besides, the inhibitory effect of these oils against these enzymes, in vitro, was confirmed, in vivo. The oral intake of these oils at a dose of (2 mL/Kg) was significantly attenuated the hyperglycemia induced by the sucrose (substrate of intestinal α-glucosidase) and the starch (substrate of pancreatic α-amylase), in the normal and STZ-diabetic rats. Although, the Roil and the UnRoil at the dose 1 mL/Kg were found that they significantly (p < 0.001) reduce the intestinal glucose absorption, in situ, with 50, 99% and 57, 97% respectively. ConclusionThe Argan oils showed a very high anti-hyperglycemic activity. This effect could be achieved by the inhibiting of the activity of pancreatic α-amylase, intestinal α-glucosidase and the intestinal absorption of D-glucose. Moreover, the UnRoil has shown a better anti-hyperglycemic activity than the Roil, which means that the torrefaction of the Argan seeds before the oil extraction, influence on the bioactive constituents responsible for this beneficial effect.

High dietary carbohydrate inclusion by both protein and lipid replacement in gilthead sea bream. Changes in digestive and absorptive processes

The effect of high amounts of dietary carbohydrates on digestive and absorptive processes was studied in juvenile gilthead sea bream. Two trials were conducted over 14 weeks. In the first trial, sea bream were fed with isoproteic diets with lipid replaced with starch and in the second with isolipidic diets with protein replaced with starch; in both wheat starch was included at above the established maximum levels for this fish species. At the end of each trial, intestinal alkaline protease, α-amylase and lipase activities were measured post-feeding, and alkaline phosphatase and leucine aminopeptidase activities and nutrient absorption capacities were measured under basal conditions.When lipid (23 to 17%) was replaced with starch (12 to 28%) in the 46% protein diet, a decrease in trypsin and chymotrypsin activities was found without modifying the trypsin/chymotrypsin ratio as dietary starch increases. Moreover, the pH of the intestinal content in the pyloric caeca increased and alkaline phosphatase activity and d-glucose absorption capacity decreased. Thus, compensatory mechanisms in buffer capacity, pancreatic enzyme activities and nutrient absorption capacities took place, allowing the maintenance of feed utilization and growth.Diets for the second trial were formulated with the lowest lipid content tested previously (17%) and protein (46 to 40%) was substituted with starch (19 to 39%). Lipase and trypsin activities increased as dietary starch raise, chymotrypsin activity and l-lysine absorption were not modified and amylase activity and d-glucose and L-alanine absorption decreased, but these digestive compensatory mechanisms were not sufficient, and there was a significant increase in FCR and a decrease in voluntary feed intake and SGR. This study suggests that sea bream are able to modulate the digestive process when protein requirements are met.

SGLT1-Mediated Transport in Caco-2 Cells Is Highly Dependent on Cell Bank Origin

The human colon adenocarcinoma (Caco-2) cell line is a well-established in vitro model for studying transport phenomena for prediction of intestinal nutrient and drug absorption. However, substances depending on transporters such predictions are complicated due to variable transporter expression and limited knowledge about transporter function during multiple cell passaging and cell thawings. In the case of sodium glucose transporter 1 (SGLT1), a key transporter of oral absorption of d-glucose, one reason for compromised prediction could be inadequate expression of SGLT1 in Caco-2 cells and thereby limited sensitivity in the determination of SGLT1-mediated permeability (PSGLT1). Here, the objective is to characterize and compare SGLT1-mediated uptake in Caco-2 cells obtained from different cell banks. SGLT1-mediated uptake of the standard SGLT1 substrate, methyl-α-d-glucopyranoside, in Caco-2 cells was shown to be highly dependent on cell bank origin. The most robust and reliable SGLT1 functionality was identified in Caco-2 cells from Deutsche Sammlung für Mikroorganismen und Zellkulturen (DSMZ), whereas cells from the American Type Culture Collection and European Collection of Authenticated Cell Cultures have lower SGLT1 transport activity. Transepithelial PSGLT1 across Caco-2 cells from DSMZ showed that PSGLT1 likely accounts for approximately 97% of absorptive methyl-α-d-glucopyranoside Papp(a-b). In conclusion, Caco-2 cells from DSMZ provide a robust in vitro model for studying SGLT1-mediated uptake and transport—over multiple cell passages and independent cell stock thawings.

Duodenal-Jejunal Bypass Improves Glycemia and Decreases SGLT1-Mediated Glucose Absorption in Rats With Streptozotocin-Induced Type 2 Diabetes

To elucidate whether duodenal-jejunal-bypass (DJB), which improves blood glucose control, changes activity of Na-D-glucose cotransporter SGLT1 in small intestine. DJB has been shown to improve oral glucose tolerance in normal rats and a genetic diabetic rat model. Because intestinal D-glucose absorption is mediated by SGLT1 localized in the brush border membrane of small intestinal enterocytes, it is unclear whether function of SGLT1 is altered by DJB and whether this contributes to the improvement of glycemic control. A high-fat diet and low-dose streptozotocin administration were used to induce a type 2 diabetes in male Lewis rats. The diabetic animals underwent DJB or sham surgery. An oral glucose tolerance test (OGTT) was used to evaluate glucose control 3 weeks after surgery. SGLT1-mediated glucose transport was assessed using everted rings of different small intestinal segments. SGLT1 mRNA expression was determined by quantitative reverse transcription polymerase chain reaction (RT-PCR). DJB improved the OGTT significantly (P < 0.001) compared with sham-operated rats while body weight was not different among the surgical groups. DJB induced a 50% reduction of SGLT1-mediated glucose uptake into enterocytes of duodenum and jejunum (P < 0.001). The concentration of D-glucose in the blood following glucose gavage increased more slowly after DJB versus sham. The data indicate that DJB surgery decreases glucose absorption in the small intestine by downregulation of SGLT1-mediated glucose uptake. We suggest that the downregulation of SGLT1 contributes to the body-weight independent improvement of diabetes type 2.

Characterization of d-Glucose Transport across Equine Jejunal Brush Border Membrane Using the Pig as an Efficient Model of Jejunal Glucose Uptake

To test the hypotheses that glucose transport capacity across the brush border membrane (BBM) of the large colon is lower than that of the small intestine in equids, and that small intestinal transport capacity in equids is lower than suids. d-glucose transport capacity (Vmax) and affinity (KM) across the BBM of the distal jejunum (DJ) and proximal large colon (PLC) of the pony and pig were measured. Mucosa was collected from the DJ and PLC of ponies (n = 4) and pigs (n = 3), flash-frozen in liquid nitrogen, and stored at −80°C. Jejunal and colonic BBM vesicles were manufactured, and d-glucose transport was determined. There was no detectable active uptake of glucose in the equine PLC. Compared with the pig DJ, d-glucose transport capacity was lower (2595 ± 331 vs. 655 ± 286 ρmol·mg protein−1·s−1, respectively, P < .01) and transport affinity tended to be lower (0.09 ± 0.07 vs. 0.27 ± 0.06 mM, respectively, P = .11) in the pony DJ. Compared with the pig DJ, d-glucose transport capacity (2,595 ± 331 vs. 571 ± 331 ρmol·mg protein−1·s−1, respectively, P < .001) and transport affinity (0.09 ± 0.07 vs. 0.54 ± 0.07 mM, respectively, P < .001) in the pig PLC were lower. Results show there is negligible d-glucose uptake across pony PLC, and capacity for d-glucose absorption across DJ BBM is fourfold lower in the pony compared with the pig. Results further exemplify, at a physiological level, the limited capacity of the equid small intestine to transport glucose relative to an omnivorous mammal, and the likely evolutionary adaptation of equids to low dietary levels of nonstructural carbohydrates.

Response to Comment on: Gorboulev et al. Na+-d-glucose Cotransporter SGLT1 Is Pivotal for Intestinal Glucose Absorption and Glucose-Dependent Incretin Secretion. Diabetes 2012;61:187–196

In response to the commentary of Professor Kellett (1), we would like to clarify the following points. The data reported in our article (2) confirm the observation that SGLT1-mediated D-glucose uptake in the presence of a high D-glucose concentration in the small intestinal lumen mediates translocation of GLUT2 to the luminal membrane of the enterocytes; however, they contradict the hypothesis that GLUT2 is the major pathway of D-glucose absorption when glucose is plentiful (3–6). Comparing SGLT1-mediated and GLUT2-mediated glucose uptake into isolated brush-border membrane (BBM) vesicles, we present evidence that SGLT1 transports about 90% of D-glucose into the enterocytes in the presence of high luminal glucose whereas only about 10% …

Na(+)-D-glucose cotransporter SGLT1 is pivotal for intestinal glucose absorption and glucose-dependent incretin secretion.

To clarify the physiological role of Na+-d-glucose cotransporter SGLT1 in small intestine and kidney, Sglt1−/− mice were generated and characterized phenotypically. After gavage of d-glucose, small intestinal glucose absorption across the brush-border membrane (BBM) via SGLT1 and GLUT2 were analyzed. Glucose-induced secretion of insulinotropic hormone (GIP) and glucagon-like peptide 1 (GLP-1) in wild-type and Sglt1−/− mice were compared. The impact of SGLT1 on renal glucose handling was investigated by micropuncture studies. It was observed that Sglt1−/− mice developed a glucose-galactose malabsorption syndrome but thrive normally when fed a glucose-galactose–free diet. In wild-type mice, passage of d-glucose across the intestinal BBM was predominantly mediated by SGLT1, independent the glucose load. High glucose concentrations increased the amounts of SGLT1 and GLUT2 in the BBM, and SGLT1 was required for upregulation of GLUT2. SGLT1 was located in luminal membranes of cells immunopositive for GIP and GLP-1, and Sglt1−/− mice exhibited reduced glucose-triggered GIP and GLP-1 levels. In the kidney, SGLT1 reabsorbed ∼3% of the filtered glucose under normoglycemic conditions. The data indicate that SGLT1 is 1) pivotal for intestinal mass absorption of d-glucose, 2) triggers the glucose-induced secretion of GIP and GLP-1, and 3) triggers the upregulation of GLUT2.

Modifications of intestinal nutrient absorption in response to dietary fish meal replacement by plant protein sources in sea bream ( Sparus aurata) and rainbow trout ( Onchorynchus mykiss)

The effects of partial (75%; diet PP75) and total (100%; diet PP100) replacement of fish meal by plant protein sources on the intestinal nutrient absorption of gilthead sea bream and rainbow trout were examined over a 12-week growth trial. The diets comprised a mixture of plant ingredients (corn gluten meal, wheat gluten, extruded peas and rapeseed meal) and met the amino acid requirements of the fish. A third group of fish on a fish meal diet was used as a control for comparative purposes. Diets were tested in triplicate and fish were fed twice a day until visual satiation. At the end of the trial, we measured amino acid ( l-leucine, l-lysine, l-phenylalanine, l-alanine and l-proline) and d-glucose absorption at short-term (6 h) and long-term (36 h and 48 h in rainbow trout and sea bream respectively) post-feeding by means of brush border membrane vesicles obtained from pyloric caeca, proximal intestine and distal intestine. The absorption pattern at 6 h post-feeding was modified in both species in response to fish meal replacement. In PP75-fed trout absorption was delayed from pyloric caeca to proximal and/or distal intestinal segments, thus total absorption capacity was maintained in this group. On the contrary, total uptake was significantly decreased in trout fed the PP100 diet and in sea bream on both PP75 and PP100 diets. Glucose transport capacity was increased in both experimental sea bream groups and in PP75 trout. Long-term transport capacity was up-regulated for both species. Our results show that intestinal nutrient absorption is modified in response to the use of high levels of plant protein sources and that these changes are species-specific.

Concentration- and region-dependent intestinal permeability of fluvastatin in the rat.

The purpose of this study was to investigate the mechanisms of transport of fluvastatin across the intestinal mucosa in various regions of the intestine in the rat. In-situ single-pass perfusions of the jejunum, ileum and colon were performed and the effective permeability (Peff) of fluvastatin, antipyrine and D-glucose were assessed in each region, at three different perfusate fluvastatin concentrations (1.6, 16 and 160 microM). The effect of lovastatin acid on the bi-directional transport of fluvastatin across the ileal mucosa was also studied. The Peff of fluvastatin was found to be dependent both on the intestinal region and on the concentration in the intestinal lumen (P < 0.001). Fluvastatin had the lowest Peff (0.55 +/- 0.10 x 10(-4) cm s(-1)) in the jejunum at 1.6 microM, and the highest Peff (1.0 +/- 0.16 x 10(-4) cm s(-1)) in the colon at 160 microM. The highest concentration of fluvastatin increased the average absorption of water from the intestine by 209% (P < 0.05), and the average Peff of D-glucose by 29% (P < 0.05). The presence of excess lovastatin acid (100 microM, compared with fluvastatin 1.6 microM) at the luminal side increased the average absorption of water by 218% (P < 0.001), and the Peff of fluvastatin in the ileum and the colon by 44 and 50%, respectively (P < 0.05). The presence of lovastatin acid on the luminal side in the ileum also increased the blood-to-lumen transport (exsorption) of fluvastatin by 43% (P < 0.001). The increased intestinal absorption of fluvastatin at higher concentrations does not suggest that substantial absorption occurs by any carrier-mediated process in the absorptive direction. The increased bi-directional transport when lovastatin acid was added to the lumen suggests that fluvastatin is not a P-glycoprotein substrate. Instead, the concentration-dependent increase in the absorption of fluvastatin, water and D-glucose suggests a direct effect of fluvastatin on the transcellular passive transport.

Inhibition of intestinal absorption by different samples of cetrimide and the homologous alkyl series C10-C20.

Abstract The effects of different samples of cetrimide on the intestinal absorption of D-glucose, sodium butyrate and DL-methionine were compared with those of homologous compounds C(10)-C(20) of the same alkyl series, by in vivo intraluminal perfusion in the mouse, rat and guinea-pig. Two samples of “cetrimide” had different inhibitory activities in the mouse and rat but were equiactive in the guinea-pig in which both samples caused glucose reversal. None of the homologues, C(10)-C(20), paralleled the activity of either of the cetrimide samples exactly. It is concluded that cetrimide should be assayed in the rat before its use in studies of absorption and protein binding.

Transepithelial D‐glucose and D‐fructose transport across lobster intestine

The mechanisms of transepithelial absorption of dietary D-glucose and D-fructose were examined in the lobster, Homarus americanus, intestine using 3H-D-glucose and 3H-D-fructose. Lobster intestines were mounted in a perfusion chamber to determine transepithelial mucosal to serosal (MS) and serosal to mucosal (SM) transport mechanisms of glucose and fructose. Both MS glucose and fructose transports, as functions of luminal [sugar], increased in a hyperbolic manner, suggesting the presence of mucosal transport proteins. Phloridzin inhibited MS flux of glucose, but not that of fructose, suggesting the presence of an SGLT1-like transporter. Immunohistochemistry analysis, using a goat anti-rabbit GLUT5 polyclonal antibody, revealed the localization of a brush border GLUT5-like fructose transport protein. MS fructose transport was decreased in the presence of mucosal phloretin, but the same effect was not observed in the MS transport of glucose. Both SM glucose and fructose transports were decreased in the presence of increasing concentrations of serosal phloretin, suggesting the presence of a shared serosal GLUT2 transport protein for both sugars. D-glucose and D-fructose transports across lobster intestine are similar to those for sugar uptake in mammalian intestine, suggesting evolutionarily conserved absorption processes for these solutes.

Insulin down-regulates the Na +/K + ATPase in enterocytes but increases intestinal glucose absorption

The effect of insulin on [ 14C] 3-O-methyl- d-glucose (3OMG) absorption in the rat jejunum was studied using an in situ perfusion technique. Insulin increased apical glucose entry into the cells and decreased intestinal retention suggesting that serosal glucose transport was enhanced by the hormone. This enhanced uptake was ascribed to an increase in the expression of glucose transporters as confirmed by Western blot analysis and not to a higher sodium gradient, since insulin reduced the activity and protein expression of the Na +/K + ATPase. To separate the glycemic from the insulinemic effect on glucose transport, the effect of the hormone was investigated in vitro using cultured Caco-2 cells. The cells also showed an increase in [ 14C] 3OMG uptake and intracellular glucose levels when treated with insulin and a lower Na +/K + ATPase activity. Phloretin, an inhibitor of GLUT2 was used to determine if these transporters are targeted by the hormone. The results showed that the effect of insulin on glucose uptake and intracellular glucose was still enhanced in presence of phloretin. Considering the inhibitory effect of the hormone on the Na +/K + ATPase, it was concluded that insulin acts by increasing the number of glucose transporters, a hypothesis that was confirmed by Western blot analysis.

Effect of dietary fatty acids on the intestinal permeability of marker drug compounds in excised rat jejunum.

The aim of this study was to explore the effects of diets containing saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and omega-3 and omega-6 polyunsaturated fatty acids (omega-3 and omega-6 PUFA, respectively) on the passive and active transport properties of rat jejunum using marker compounds. Rats were fed diets supplemented with 18.4% (w/w) lipid (4 groups) or standard rat chow (1 group) for a period of 30 days. At the end of the dietary period, mucosal scrapings were taken for the determination of membrane phospholipids, and the apparent jejunal permeability of radiolabelled marker compounds was determined using modified Ussing chambers. Changes in the phospholipid content of the brush border membrane reflected the different lipid content of the diets. The passive paracellular permeability of mannitol was not significantly affected by the fatty acid composition of the diet, although there was a trend toward decreased mannitol permeability in the rats fed both the omega-3 and omega-6 PUFA diets. In comparison, the transcellular diffusion of diazepam was reduced by 20% (P < 0.05) in rats fed diets supplemented with omega-3 and omega-6 PUFA. In the lipid-fed rats, the serosal to mucosal flux of digoxin, an intestinal P-glycoprotein substrate, was reduced by 20% (P < 0.05) relative to the chow-fed group, however there were no significant differences between the different lipid groups. The active absorption of D-glucose via the Na+-dependent transport pathway was highest in the SFA, MUFA and PUFA omega-3 dietary groups, intermediate in the low-fat chow group and lowest in the PUFA omega-6 group, and was positively correlated with short-circuit current. These studies indicate that dietary fatty acid changes can result in moderate changes to the active and passive transport properties of excised rat jejunum.

Mechanistic bases for differences in passive absorption

Increasing evidence indicates that small birds have more extensive non-mediated, paracellular intestinal absorption of hydrosoluble compounds than do mammals, although studies have not employed uniform methodologies or demonstrated differences at the tissue level. The mechanistic bases behind apparent species differences are poorly understood. We show using uniform methodology at the whole-animal level that intact, unanesthetized pigeons had significantly higher absorption of l-arabinose and l-rhamnose, two water-soluble compounds used to measure paracellular absorption, than similarly sized laboratory rats. The species differences were also evident using perfused isolated loops of duodenum, showing that the difference in paracellular absorption occurred at the tissue level, even when d-glucose absorption rates (transcellular+paracellular) were similar between the two species. The greater absorption of these probes in pigeons could not be explained by mediated uptake of the putative paracellular probes, or by increased nominal surface area, increased villus area or increased number of tight junctions. Rats and pigeons had comparable absorption of larger probes, which is consistent with similar effective pore size of the tight junction between enterocytes. The elimination of these mechanistic explanations might suggest that pigeon intestine has relatively higher paracellular solvent drag, but pigeon duodenal segments did not have higher net water absorption than rat duodenal segments. Whatever the exact mechanism(s), the paracellular pathway of both species limits substantial (>5%) fractional absorption to molecules smaller than about 4.8 A (M(r) ca. 350), and permeability to smaller molecules at the tissue level is higher in pigeons than in rats.

L-proline transport by purified cell types of lobster hepatopancreas

The hepatopancreas of the American lobster, Homarus americanus, has four epithelial cell types that are anatomically distinguishable and can be separated for in vitro investigation of their individual biological roles in the intact organ using centrifugal elutriation. Previous studies employing this separation method have produced hepatopancreatic cell suspensions that have been used to examine the nature of copper transport, 2 Na+/1 H+ exchange, and D-glucose absorption by each cell type in isolation from the other cells comprising the tubular epithelium. The present investigation used this method to study amino acid transport by E-, F-, R-, and B-cells of the lobster hepatopancreas in order to characterize the absorption processes for protein digestion products by this organ and to identify which cell type was most likely the responsible agent for net transcellular transfer of these organic molecules from lumen to blood. Results indicated that heptopancreatic E- and F-cell types were the only cells exhibiting Na+-dependent 3H-L-proline transport. Further examination of 3H-L-proline influx by F-cell suspensions indicated that this cell type possessed plasma membrane Na+-dependent IMINO-like and B0-like transport mechanisms and Na+-independent L-like transport mechanisms. Using selective inhibitors of these separate transport systems (e.g., L-pipecolate, L-alanine, and L-leucine), the IMINO-like transporter appeared to predominate in L-proline influx into F-cells, while lesser amounts of amino acid transport took place by the B0-like and L-like systems. The results of this study suggest that the hepatopancreatic F-cell is the epithelial cell type responsible for the bulk of amino acid absorption by this organ and that the IMINO-like transporter is responsible for most of the L-proline transfer through this agent. It is further suggested that as digestion and absorption proceeds in the hepatopancreas and concentrations of luminal amino acids and sodium fall, Na+-dependent transport systems, like the IMINO-like and B0-like, increase their binding affinities for their substrates to maximize nutrient transfer across the epithelium.