Intestinal adaptation to diabetes. Altered Na-dependent nutrient absorption in streptozocin-treated chronically diabetic rats

Vitamin E (α-Tocopherol) Does Not Ameliorate the Toxic Effect of Bisphenol S on the Metabolic Analytes and Pancreas Histoarchitecture of Diabetic Rats

This study investigated whether the coadministration of vitamin E (VitE) diminishes the harmful effects provoked by plasticizer bisphenol S (BPS) in the serum metabolites related to hepatic and renal metabolism, as well as the endocrine pancreatic function in diabetic male Wistar rats. Rats were divided into five groups (n = 5-6); the first group was healthy rats (Ctrl group). The other four groups were diabetic rats induced with 45 mg/kg bw of streptozotocin: Ctrl-D (diabetic control); VitE-D (100 mg/kg bw/d of VitE); BPS-D (100 mg/kg bw/d of BPS); The animals from the VitE + BPS-D group were administered 100 mg/kg bw/d of VitE + 100 mg/kg bw/d of BPS. All compounds were administered orally for 30 days. Body weight, biochemical assays, urinalysis, glucose tolerance test, pancreas histopathology, proximate chemical analysis in feces, and the activity of antioxidants in rat serum were assessed. The coadministration of VitE + BPS produced weight losses, increases in 14 serum analytes, and degeneration in the pancreas. Therefore, the VitE + BPS coadministration did not have a protective effect versus the harmful impact of BPS or the diabetic metabolic state; on the contrary, it partially aggravated the damage produced by the BPS. VitE is likely to have an additive effect on the toxicity of BPS.

Mechanisms of weight loss and improved metabolism following bariatric surgery

Bariatric surgery is increasingly recognized as one of the most effective interventions to help patients achieve significant and sustained weight loss, as well as improved metabolic and overall health. Unfortunately, the cellular and physiological mechanisms by which bariatric surgery achieves weight loss have not been fully elucidated, yet are critical to understanding the central role of the intestinal tract in whole-body metabolism and to developing novel strategies for the treatment of obesity. In this review, we provide an overview of potential mechanisms contributing to weight loss, including effects on regulation of energy balance and both central and peripheral nervous system regulation of appetite and metabolism. Moreover, we highlight the importance of the gastrointestinal tract, including alterations in bile acid physiology, secretion of intestinally derived hormones, and the microbiome, as a potent mediator of improved metabolism in postbariatric patients.

Glucose transporters: cellular links to hyperglycemia in insulin resistance and diabetes

Abnormal expression and/or function of mammalian hexose transporters contribute to the hallmark hyperglycemia of diabetes. Due to different roles in glucose handling, various organ systems possess specific transporters that may be affected during the diabetic state. Diabetes has been associated with higher rates of intestinal glucose transport, paralleled by increased expression of both active and facilitative transporters and a shift in the location of transporters within the enterocyte, events that occur independent of intestinal hyperplasia and hyperglycemia. Peripheral tissues also exhibit deregulated glucose transport in the diabetic state, most notably defective translocation of transporters to the plasma membrane and reduced capacity to clear glucose from the bloodstream. Expression of renal active and facilitative glucose transporters increases as a result of diabetes, leading to elevated rates of glucose reabsorption. However, this may be a natural response designed to combat elevated blood glucose concentrations and not necessarily a direct effect of insulin deficiency. Functional foods and nutraceuticals, by modulation of glucose transporter activity, represent a potential dietary tool to aid in the management of hyperglycemia and diabetes.

The role of gut adaptation in the potent effects of multiple bariatric surgeries on obesity and diabetes

Bariatric surgical procedures such as vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass (RYGB) are the most potent treatments available to produce sustained reductions in body weight and improvements in glucose regulation. While traditionally these effects are attributed to mechanical aspects of these procedures, such as restriction and malabsorption, a growing body of evidence from mouse models of these procedures points to physiological changes that mediate the potent effects of these surgeries. In particular, there are similar changes in gut hormone secretion, bile acid levels, and composition after both of these procedures. Moreover, loss of function of the nuclear bile acid receptor (FXR) greatly diminishes the effects of VSG. Both VSG and RYGB are linked to profound changes in the gut microbiome that also mediate at least some of these surgical effects. We hypothesize that surgical rearrangement of the gastrointestinal tract results in enteroplasticity caused by the high rate of nutrient presentation and altered pH in the small intestine that contribute to these physiological effects. Identifying the molecular underpinnings of these procedures provides new opportunities to understand the relationship of the gastrointestinal tract to obesity and diabetes as well as new therapeutic strategies to harness the effectiveness of surgery with less-invasive approaches.

Metabolic and molecular action of Trigonella foenum-graecum (fenugreek) and trace metals in experimental diabetic tissues

Diabetes mellitus is a heterogeneous metabolic disorder characterized by hyperglycaemia resulting in defective insulin secretion, resistance to insulin action or both. The use of biguanides, sulphonylurea and other drugs are valuable in the treatment of diabetes mellitus; their use, however, is restricted by their limited action, pharmacokinetic properties, secondary failure rates and side effects. Trigonella foenum-graecum, commonly known as fenugreek, is a plant that has been extensively used as a source of antidiabetic compounds from its seeds and leaf extracts. Preliminary human trials and animal experiments suggest possible hypoglycaemic and antihyperlipedemic properties of fenugreek seed powder taken orally. Our results show that the action of fenugreek in lowering blood glucose levels is almost comparable to the effect of insulin. Combination with trace metal showed that vanadium had additive effects and manganese had additive effects with insulin on in vitro system in control and diabetic animals of young and old ages using adipose tissue. The Trigonella and vanadium effects were studied in a number of tissues including liver, kidney, brain peripheral nerve, heart, red blood cells and skeletal muscle. Addition of Trigonella to vanadium significantly removed the toxicity of vanadium when used to reduce blood glucose levels. Administration of the various combinations of the antidiabetic compounds to diabetic animals was found to reverse most of the diabetic effects studied at physiological, biochemical, histochemical and molecular levels. Results of the key enzymes of metabolic pathways have been summarized together with glucose transporter, Glut-4 and insulin levels. Our findings illustrate and elucidate the antidiabetic/insulin mimetic effects of Trigonella, manganese and vanadium.

Ileal apical Na+-dependent bile acid transporter ASBT is upregulated in rats with diabetes mellitus induced by low doses of streptozotocin

Increased intestinal bile acid absorption and expansion of the bile acid pool has been implicated in the hypercholesterolemia associated with diabetes mellitus. However, the molecular basis of the increase in bile acid absorption in diabetes mellitus is not fully understood. The ileal apical Na(+)-dependent bile acid transporter (ASBT) is primarily responsible for active reabsorption of the majority of bile acids. Current studies were designed to investigate the modulation of ASBT function and expression in streptozotocin (STZ)-induced diabetes mellitus in rats and to examine the effect of insulin on rat ASBT promoter by insulin. Diabetes mellitus was induced in Sprague-Dawley rats by intraperitoneal injection of low doses of STZ (20 mg/kg body wt) on five consecutive days. Human insulin (10 U/day) was given to a group of diabetic rats for 3 days before euthanasia. RNA and protein were extracted from mucosa isolated from the small intestine and ASBT expression was assessed by real-time quantitative RT-PCR and Western blotting. Our data showed that ASBT mRNA and protein expression were significantly elevated in diabetic rats. Insulin treatment of diabetic rats reversed the increase in ASBT protein expression to control levels. Consistently, ileal Na(+)-dependent [(3)H]taurocholic uptake in isolated intestinal epithelial cells was significantly increased in diabetic rats. In vitro studies utilizing intestinal epithelial Caco-2 cells demonstrated that ASBT expression and promoter activity were significantly decreased by insulin. These studies demonstrated that insulin directly influences ASBT expression and promoter activity and that ASBT function and expression are increased in rats with STZ-induced diabetes mellitus. The increase in ASBT expression may contribute to disturbances in cholesterol homeostasis associated with diabetes mellitus.

Immediate insulin treatment prevents gut motility alterations and loss of nitrergic neurons in the ileum and colon of rats with streptozotocin-induced diabetes

The streptozotocin-induced diabetic rat model was used to investigate the relation between the deranged gut motility and the segment-specific quantitative changes in the nitrergic myenteric neurons. Additionally, we studied the effectiveness of early insulin replacement to prevent the diabetes-induced changes. Rats were divided into three groups: controls, diabetics and insulin-treated diabetics. Ten weeks after the onset of diabetes, animals were chosen from each group for intestinal transit measurements. The remainder were killed and gut segments were processed for NADPH-diaphorase histochemistry and HuC/HuD immunohistochemistry. The diabetic rats displayed faster transit than that for the controls. In the insulin-treated group, the transit time was the same as that in the controls. In the duodenum of the diabetic rats, the number of nitrergic neurons was decreased, while the total neuronal number was not altered. In the jejunum, ileum and colon, both the total and the nitrergic neuronal cell number decreased significantly. Insulin treatment did not prevent the nitrergic cell loss significantly in the duodenum and jejunum, but it did prevent it significantly in the ileum and colon. These findings comprise the first evidence that the nitrergic neurons located in different intestinal segments exhibit different susceptibilities to a diabetic state and to insulin treatment.

Therapy Insight: gastrointestinal complications of diabetes--pathophysiology and management

Patients with diabetes often have gastrointestinal symptoms, but the extent and severity of this problem and the specificity of the symptoms are not nearly as well defined as frequently assumed. Any part of the gastrointestinal tract can be affected, and the presenting symptoms depend on the composite of dysfunctional elements. Gastroesophageal reflux, Candida esophagitis, gastroparesis, diarrhea and constipation are among the many common gastrointestinal complications of diabetes. No specific risk factor for the development of these complications has been identified and their etiology is most likely to be multifactorial, involving both reversible and irreversible processes. Treatment should be directed at tighter glycemic and symptom control, which can bring about clinical improvement for many patients. For other patients, however, effective clinical management is problematic because no therapies are available to prevent or correct the underlying disease mechanisms. Studies now suggest that reduced levels of key trophic factors cause transdifferentiation of pacemaker interstitial cells of Cajal into a smooth-muscle-like phenotype. If this really is the case, therapies directed at restoring the normal milieu of trophic signals could correct the dysfunction of the interstitial cells of Cajal and resolve many gastrointestinal complications. Advances in stem cell technology also hold promise to provide a cure for diabetes and to correct abnormalities in gastrointestinal pathology.

The effects of insulin on glucose and fluid transport in the isolated small intestine of normal rats

Chronically administered insulin returns enhanced maximal glucose transport capacity induced by diabetes to its normal state. In this study, the direct and acute effects of insulin on glucose transport in different parts of isolated small intestine were investigated. Mucosal Fluid Transport (MFT), Mucosal Glucose Transport (MGT) and Serosal Glucose Transport (SGT) were measured in the presence and absence of insulin in averted sacs, prepared from female Wistar rats. This study shows that the presence of insulin in vitro (40 and 80 microU/mL) can reduce MGT and SGT in different segments of the small intestine (duodenum, jejunum and ileum) after 30 min whereas it had no effect on MFT. Mucosal glucose transfer rates in the duodenum, jejunum and ileum of the controls were 6.07+/-0.4, 6.34+/-0.62 and 6.43+/-0.47 mg/g tissue respectively which were significantly reduced to 3.82+/-0.93, 3.60+/-0.50 and 1.17+/-0.45 in the presence of 80 microU/mL of insulin. Serosal glucose transfer too was decreased significantly from 0.3+/-0.05, 0.57+/-0.07 and 0.43+/-.07 in the duodenum, jejunum and ileum to 0.16+/-0.03, 0.16+/-0.04 and .07+/-.02 respectively. Mucosal fluid transfer was not affected by insulin. Insulin was as effective whether it was added on the mucosal or the serosal side. The results of this study show that insulin can directly affect glucose transport in the small intestine; its physiological role must be examined. Direct effect of insulin deficiency on glucose absorption in diabetic patients may play a role in the pathophysiology of the disease.

Low doses of vanadate and Trigonella synergistically regulate Na+/K + -ATPase activity and GLUT4 translocation in alloxan-diabetic rats

Oral administration of vanadate to diabetic animals have been shown to stabilize the glucose homeostasis and restore altered metabolic pathways. However, vanadate exerts these effects at relatively high doses with several toxic effects. Low doses of vanadate are relatively safe but unable to elicit any antidiabetic effects. The present study explored the prospect of using low doses of vanadate with Trigonella foenum graecum, seed powder (TSP), another antidiabetic agent, and to evaluate their antidiabetic effect in diabetic rats. Alloxan diabetic rats were treated with insulin, vanadate, TSP and low doses of vanadate with TSP for three weeks. The effect of these antidiabetic compounds was examined on general physiological parameters, Na(+)/K(+) ATPase activity, membrane lipid peroxidation and membrane fluidity in liver, kidney and heart tissues. Expression of glucose transporter (GLUT4) protein was also examined by immunoblotting method in experimental rat heart after three weeks of diabetes induction. Diabetic rats showed high blood glucose levels. Activity of Na(+)/K(+) ATPase decreased in diabetic liver and heart. However, kidney showed a significant increase in Na(+)/K(+) ATPase activity. Diabetic rats exhibited an increased level of lipid peroxidation and decreased membrane fluidity. GLUT4 distribution was also significantly lowered in heart of alloxan diabetic rats. Treatment of diabetic rats with insulin, TSP, vanadate and a combined therapy of lower dose of vanadate with TSP revived normoglycemia and restored the altered level of Na(+)/K(+) ATPase, lipid peroxidation and membrane fluidity and also induced the redistribution of GLUT4 transporter. TSP treatment alone is partially effective in restoring the above diabetes-induced alterations. Combined therapy of vanadate and TSP was the most effective in normalization of altered membrane linked functions and GLUT4 distribution without any harmful side effect.

Human small bowel storage: the role for luminal preservation solutions

BACKGROUND

Graft injury incurred during periods of cold storage remains a factor affecting the success of small bowel (SB) transplantation. No one preservation solution, including the gold standard University of Wisconsin (UW) solution, has been able to maintain graft integrity for storage periods paralleling that of other commonly transplanted intra-abdominal organs. We investigated the role for the luminal administration of preservation solutions in a small animal model, documenting significantly improved graft quality. The current study addresses direct clinical applicability using human SB.

METHODS

Human SB was obtained at the time of standard multiviscera procurement. After a common intra-arterial UW flush, the SB was immediately removed from the abdomen, randomly divided into three segments, and treated as follows (n=6-9): group 1, no luminal flush; group 2, luminal flush with UW solution; and group 3, luminal flush with an amino acid- enriched solution. Analysis of cellular energetics, permeability, and histologic injury was performed throughout 24 hr of cold storage.

RESULTS

Mucosal barrier function, measured by mannitol permeability, was significantly better overall in groups 2 and 3, with 24-hr values measuring 31 and 34 nmol/cm2/hr versus 57 nmol/cm2/hr, respectively (both P<0.05). Significantly less morphologic injury was also noted in the luminally treated specimens (groups 2 and 3) compared with the clinical standard (vascular flush with UW solution). Damage in group 1 reached gross villus denudation with an obvious elevated risk of villus tissue loss, whereas groups 2 and 3 only exhibited epithelial clefting to varying degrees.

CONCLUSION

This study supports luminal administration of preservation solutions for improvement of human SB graft quality during clinically relevant periods of cold storage.

Defining the role of a tailored luminal solution for small bowel preservation

The mucosal layer is the initial site of small bowel (SB) graft injury sustained during cold storage. Vascular administration of preservation solutions alone is unable to prevent ischemic injury of this layer during clinically relevant storage periods. The SB is unique in that it possesses both a vascular and a luminal route by which preservation solutions can be administered. We hypothesized that addition of a luminal-delivered solution, formulated on amino acid requirements for energy- and non-energy-related reactions, would provide site-specific preservation of mucosal energetics, barrier function and morphology throughout an extended period of cold storage. Of the three luminal solutions containing amino acids which were tested (UWG, AA1, AA2), only the two groups (AA1, AA2), containing glutamine plus 18 other amino acids, +/- osmotic agent (lactobionate) and buffer (BES), exhibited significant improvements in energetics, barrier function, and histology compared to the clinical standard of isolated vascular University of Wisconsin (UW) solution. Although the AA1 and AA2 groups preserved barrier function and morphology up to 24h better than all other solutions tested, AA2 proved to be the only luminal solution with values of permeability, conductance, and short-circuit current not significantly different from freshly isolated tissues. Furthermore, the greatest reduction in histologic injury was effected by AA2 treatment (median grade 2 compared to control, UW(v), grade 8). This study documents that a luminal-delivered solution, formulated on physiologic SB requirements, provides targeted preservation of the SB mucosa.

Potentiating the benefit of vascular-supplied glutamine during small bowel storage: importance of buffering agent

BACKGROUND

Glutamine (gln)-supplemented University of Wisconsin (UW) solution improves overall small bowel (SB) preservation. Sustained gln metabolism in a system devoid of hepatic detoxification will necessarily result in the accumulation of pH active end products leading to nonphysiologic pH shifts. We hypothesized that simultaneous addition of N,N-bis[2-hydroxyethyl]-2-aminoethane sulfonic acid (BES), a known buffering agent, would potentiate the beneficial effect of gln supplementation by addressing the fundamental metabolic principle of pH homeostasis.

METHODS

Sprague-Dawley SB rats were administered a vascular flush with one of four solutions: UW; UW+90 mM BES (UWB); UW+2% gln (UWG); or UW+2% gln+90 mM BES (UWBG). Indices of energetics, barrier function, gln catabolism, and histology (light and electron microscopy) were assessed over a 10-hr cold storage time course.

RESULTS

Superior gln utilization in the UWBG group was indicated by elevated levels of key catabolites (glutamate, aspartate, glycine, ammonia). The addition of BES and gln resulted in significantly higher levels of all energetic parameters (ATP, total adenylates) at 10 hr compared with UW, UWB, and/or UWG. Barrier function was markedly improved after 10 hr storage in the UWBG group; mannitol permeability was 169 nmol/cm2/hr versus 572 and 445 nmol/cm(2)/hr (for UW and UWG, respectively). Histologic injury at 10 hr was 5.5, 7.5, and 8 (Park's grade) for UWBG, UWG, and UW. Ultrastructural damage was markedly reduced with UWBG, as assessed by grade of mitochondria damage.

CONCLUSION

This study strongly supports that the beneficial effects of gln-enriched UW solution can be amplified when combined with an effective buffering agent such as BES.

Adverse gastrointestinal effects of mycophenolate mofetil: aetiology, incidence and management

Mycophenolate mofetil (MMF) is a relatively new immunosuppressive drug. It inhibits inosine monophosphate dehydrogenase, a key enzyme in the de novo pathway of purine synthesis, and thus causes lymphocyte-selective immunosuppression. Large clinical trials have revealed the efficacy of MMF in the prevention of allograft rejection when administered together with cyclosporin or tacrolimus and corticosteroids. Although the adverse effect profile of MMF is comparatively benign, gastrointestinal adverse effects are a major concern. These effects are partially explained by the increased immune suppression, by the mode of action and by interactions, particularly with other immunosuppressants. The aetiology of the rarest gastrointestinal adverse effects is still not completely clear. Therapy depends upon the clinical gravity of the adverse effects and is therefore a case of waiting and ob- serving. An adjustment of dosage of immunosuppressants according to the clinical situation and, particularly in the case of MMF, spreading the total dosage over more than 2 daily doses are often sufficient. Should adverse effects persist for a longer period of time and be of a more serious nature, a comprehensive invasive diagnostic process is necessary, including endoscopy and biopsy and the search for opportunistic infections. In this case, dosage reduction or the complete withdrawal of MMF seems to be unavoidable. Severe gastrointestinal complications with MMF are rare, but when they do occur they may require extensive diagnosis and treatment. In the future, therapeutic drug monitoring and, where necessary, pharmacological modifications of MMF could lead to a further reduction of adverse effects with an equal or even increased efficacy.

Nutritional effects of surgical and medical treatment for short bowel syndrome

BACKGROUND

The choice of treatment options in short bowel syndrome (SBS) is hampered by a lack of comparative studies. This study uses a previously validated juvenile pig model of SBS to compare nontreated controls (C), surgical treatment with either proximal colon interposition (CI) or bowel lengthening (BL), with medical treatment with codeine and cimetidine (M).

METHODS

Treatment was initiated 6 weeks after resection of 75% of the small bowel, and animals were followed until sacrifice at week 16. Feed intake and weight gain were monitored throughout; in vivo nutrient absorption, in vitro nutrient transport, sodium-glucose cotransporter activity, and intestinal morphology (gross and microscopic) were examined at the end of treatment.

RESULTS

BL and M treatments resulted in improved rates of weight gain; this improvement was associated with improved absorption of dietary fat. The treatments did not affect carbohydrate or protein absorption in vivo. In vitro fatty acid absorption was not increased in any group. Active uptake of glucose was increased in the colon interposition group, but phlorizin binding (reflecting sodium glucose cotransporter activity) did not differ between groups. Gross serosal and microscopic mucosal surface areas increased in all groups; however, there were no significant differences between the treatment groups.

CONCLUSIONS

These results demonstrate that bowel lengthening and medical treatment improved the rate of weight gain in this model of SBS. This appeared to be due to improvement in the absorption of dietary fat, which was not caused by alterations in in vitro uptake or mucosal surface area, suggesting these treatments have their affects by altering motility or intraluminal digestion. These findings suggest that these treatments are worthy of further study in treating patients (primary pediatric) with SBS.

Effect of streptozotocin-induced diabetes on rat liver Na+/K+-ATPase

Na+/K+-ATPase during diabetes may be regulated by synthesis of its alpha and beta subunits and by changes in membrane fluidity and lipid composition. As these mechanisms were unknown in liver, we studied in rats the effect of streptozotocin-induced diabetes on liver Na+/K+-ATPase. We then evaluated whether fish oil treatment prevented the diabetes-induced changes. Diabetes mellitus induced an increased Na+/K+-ATPase activity and an enhanced expression of the beta1 subunit; there was no change in the amount of the alpha1 and beta3 isoenzymes. Biphasic ouabain inhibition curves were obtained for diabetic groups indicating the presence of low and high affinity sites. No alpha2 and alpha3 isoenzymes could be detected. Diabetes mellitus led to a decrease in membrane fluidity and a change in membrane lipid composition. The diabetes-induced changes are not prevented by fish oil treatment. The results suggest that the increase of Na+/K+-ATPase activity can be associated with the enhanced expression of the beta1 subunit in the diabetic state, but cannot be attributed to changes in membrane fluidity as typically this enzyme will increase in response to an enhancement of membrane fluidity. The presence of a high-affinity site for ouabain (IC50 = 10-7 M) could be explained by the presence of (alphabeta)2 diprotomeric structure of Na+/K+-ATPase or an as yet unknown alpha subunit isoform that may exist in diabetes mellitus. These stimulations might be related, in part, to the modification of fatty acid content during diabetes.

Hormonal therapy for short bowel syndrome

PURPOSE

Treatment of short bowel syndrome (SBS) can be difficult; this study examines the effect of parental administration of different peptide hormones in a rat model of SBS.

METHODS

Juvenile male Lewis rats (220 to 240 g) underwent resection of the proximal 90% of small bowel and were assigned randomly to treatment groups: growth hormone (GH), insulinlike growth factor-1 (IGF-1), glucagonlike peptide-2 (GLP-2; given as ALX-0600, a potent protease resistant analogue of the human GLP-2), control-resected (Con-R), or control-transected (Con-T). Drugs were delivered by continuous subcutaneous infusion via Alzet mini-pumps: controls received equivalent volumes of drug vehicle. Animals were pair-fed (23 g chow per day) and followed up for 14 days monitoring weight gain. Animals were killed and active transport, hormone profiles, and intestinal morphology were assessed.

RESULTS

Hormonal treatments significantly increased weight gain in all groups (GH, 9.9+/-4.9; IGF-1, 6.0+/-9.6; and GLP-2, 0.8+/-2.7 v. -6.2+/-4.7 in untreated resected animals [weight as percentile initial weight]). This was associated with a significant alteration in intestinal morphology in the IGF-1-treated animals, and an increase in glucose transport rates in all hormonally treated animals when compared with untreated control resected animals.

CONCLUSIONS

These results show that IGF-1, GH, and GLP-2 all improve short-term weight gain after massive bowel resection in a rat model. The effects seen on weight gain may be caused by improved dietary nutrient absorption from an increase in the intestinal surface area or increase in transporting activity or alterations in the metabolic efficiency of the animal. These findings suggest further studies of these therapies as treatment for short-bowel syndrome are indicated.

Antioxidant action and potential antidiabetic properties of an isoflavonoid-containing soyabean phytochemical extract (SPE)

The potential role of oestrogenic agents, antioxidants and intestinal glucose-uptake inhibitors in the treatment of diabetes is briefly reviewed. Reports in the literature suggest that oestrogen replacement therapy may favourably modulate glucose homeostasis. A soya phytochemical extract (SPE) containing the isoflavone phytoestrogens genistein and daidzein (mostly in their glycone forms as genistin and daidzin) was investigated as an antioxidant and modulator of intestinal glucose-transport. In the present study, SPE was found to protect against glucose-induced oxidation of human low density lipoproteins (LDL) in vitro. Equol (a gut bacterial metabolite of daidzein) was a more effective antioxidant than daidzein or genistein in this system and was of similar antioxidant potency to the dietary flavonols quercetin and kaempferol and to the endogenous antioxidant 17beta-oestradiol. SPE was found to be an inhibitor of glucose uptake into rabbit intestinal brush border membrane vesicles in vitro, though of weaker potency than the classical sodium dependent glucose transporter (SGLT) inhibitor, phlorizin. Thus SPE displays a range of properties which may be of benefit in diabetes, namely as an oestrogenic agent, an inhibitor of intestinal glucose-uptake and a preventive agent for glucose-induced lipid peroxidation.

Effect of glycemic control on plasma plant sterol levels and post-heparin diamine oxidase activity in type 1 diabetic patients

We examined the effect of glycemic control on the plasma plant sterol levels (a measure of cholesterol absorption efficacy) and the plasma post-heparin diamine oxidase (DAO) activity (a measure of intestinal mucosal mass) in type 1 diabetes. The plasma plant sterol levels (mmol/mol of cholesterol) and the DAO activities after 30 U/kg of intravenous heparin were determined in age- and sex-matched three groups (12 type 1 diabetic patients undergoing conventional insulin therapy, ten patients undergoing intensive insulin therapy, and ten normal subjects). All patients continued their indicated insulin regimen for 14 days with a weight-maintaining energy restricted diet. The conventional group showed a significant higher (p < 0.001) level of the fasting plasma glucose (FPG) or the glycated albumin (GA), a higher (P < 0.01) DAO activity (2-fold of the peak level), which was observed 10-30 min after the heparin injection, and a higher (P < 0.01) plasma plant sterol levels (1.5-fold) compared with those in the other two groups, respectively. The DAO activity 30 min after the heparin injection significantly correlated with either the glycated albumin (GA) concentration or the plant sterol levels in all subjects. Furthermore, the acute glycemic control by the changes of insulin regimen from conventional to intensive showed a significant reduction of the DAO activity and plant sterols in the same patients. These results suggest that glycemic control in part relates to the intestinal adaptation to cholesterol absorption efficacy in type 1 diabetes.

Effect of combined immunosuppressive drug therapy on small intestinal nutrient transport in the rat

OBJECTIVE

Prevention of rejection and preservation of graft function remain as obstacles to clinical small intestinal transplantation (SIT). This study evaluated the effects of combined immunosuppressive agents (FK506, Rapamycin, and Mycophenolate Mofetil) on intestinal function and animal well being.

METHODS

Screening for additive toxicity was done in experiment one (D1, n = 10); doses were: FK506 0.3 mg/kg/d, Rapamycin 2 mg/kg/d, and Mycophenolate Mofetil 20 mg/kg/d, orally once daily. Control animals (C1, n = 10) received equivalent vehicle. In the second phase of the experiment, the effect of an additional parenteral treatment phase was investigated, with drug treated animals (D2, n = 6) received FK506 0.3 mg/kg, Rapamycin 1 mg/kg, and Mycophenolate Mofetil 10 mg/kg sq q12h for 1 week followed by FK506 3 mg/kg, Rapamycin 1 mg/kg, and Mycophenolate Mofetil 10 mg/kg p.o. q12h for 4 weeks. Control animals (C2, n = 6) received equivalent vehicle. Parameters followed were weight gain, nutrient absorption, drug levels and nutrient transport in vitro.

RESULTS

Controls grew normally, while weight gain was significantly reduced in drug treated animals: This was paralleled by a reduction in dietary fat absorption. Drug levels were low to therapeutic for all drugs in both experiments; FK506 appeared to affect Rapamycin and Mycophenolate Mofetil metabolism, increasing levels of both as FK506 doses increased. Nutrient transport was either not effected (D1) or increased (D2).

CONCLUSIONS

We conclude that low dose combination immunosuppressive therapy inhibits weight gain, without affecting absorption of dietary energy, or adversely affecting glucose transport. We postulate a systemic metabolic cause, which requires additional investigation at the cellular level; additional studies are also required to determine if the additive immunosuppression outweigh the side effects for SIT.

Oral administration of rapamycin and cyclosporine differentially alter intestinal function in rabbits

The immunosuppressive drugs rapamycin (Rap) and cyclosporine A (CsA) are used clinically to modify or abolish immune-mediated functions. This study examined the effect of orally administered regimens of Rap, CsA, and a combination of Rap/CsA on intestinal function in male New Zealand white rabbits. Animals received oral doses of CsA (15 mg/kg/body weight/day), low-dose (LD) and high-dose (HD) Rap (0.25 or 1 mg/kg/body wt/day, respectively), or Rap/CsA (0.25 and 5 mg/kg/body wt/day, or 0.5 and 5 mg/kg/body wt/day, respectively) for 20 days. We measured in vitro uptake of nutrients and permeability, and morphometric measurements in the jejunum and ileum were made. Animals receiving HD-Rap or HD-Rap/CsA had decreased food intake, body weight, and intestinal weight, when compared with LD-Rap, LD-Rap/CsA, CsA, or controls. The maximal transport rate (Vmax) for the active jejunal uptake of D-glucose was increased in HD-Rap and CsA, but not in the HD-Rap/CsA-treated animals. The jejunal Vmax of D-glucose in the LD-Rap- or -Rap/CsA-treated animals was no different from controls. In the HD-Rap- and HD-Rap/ CsA-treated animals, jejunal rates of uptake of stearic, linoleic, and linolenic acids were reduced when compared with controls. Jejunal and ileal permeability (as assessed by the passive uptake of L-glucose, tissue conductance, and mucosal-to-serosal flux of [3H]inulin) was increased in animals treated with HD-Rap or HD-Rap/CsA, when compared with CsA or controls. These parameters of permeability were no different at lower doses of Rap or Rap/CsA. The jejunal and ileal villous surface area was increased in CsA, but decreased in HD-Rap or HD-Rap/CsA animals. Thus, HD-Rap given alone or in combination with CsA reduced body weight gain, in part due to reduced food intake and malabsorption of lipids, which was due at least in part to reduced intestinal surface area. The relevance of these findings to patients undergoing chronic immunosuppressive drug therapy needs to be established.

Stanniocalcin: a novel protein regulating calcium and phosphate transport across mammalian intestine

Stanniocalcin (STC) is an anti-hypercalcemic glycoprotein hormone previously identified in the corpuscles of Stannius in bony fish and recently in the human genome. This study undertook to express human STC in Chinese hamster ovary (CHO) cells and to determine its effects on calcium and phosphate absorption in swine and rat intestine. Unidirectional mucosal-to-serosal (Jm-->s) and serosal-to-mucosal (Js-->m) 45Ca and 32P fluxes were measured in vitro in duodenal tissue in voltage-clamped Ussing chambers. Addition of STC (10-100 ng/ml) to the serosal surface of the duodenum resulted in a simultaneous increase in calcium Jm-->s and Js-->m fluxes, with a subsequent reduction in net calcium absorption. This was coupled with an STC-stimulated increase in phosphate absorption. Intestinal conductance was increased at the highest dose of STC (100 ng/ml) in swine tissue. The addition of STC to the mucosal surface had no effect on calcium and phosphate fluxes. STC at doses of 10-1,000 ng/ml had no effect on short-circuit current in any region of the rat intestine. In conclusion, human recombinant STC decreases the absorption of calcium and stimulates the absorption of phosphate in both swine and rat duodenum. STC is a novel regulatory protein that regulates mammalian intestinal calcium and phosphate transport.

Expression of rac1 protein in the crypt-villus axis of rat small intestine: in reference to insulin action

The expression of rho family along the crypt-villus axis of rat small intestine was investigated. The immunoblot analysis showed that the content of rac1 protein gradually increased from tip-villus to crypt-villus enterocytes without changes in the contents of rhoA and rac2 proteins. Furthermore, the contents of rac1 protein in the entire enterocytes were markedly decreased in streptozotocin-induced diabetic rats and restored by short-term treatment with insulin. These results suggest that differentiation and proliferation in the enterocytes of rat small intestine are possibly related to the expression of rac1 protein through insulin action.

Adaptation of intestinal nutrient transport in health and disease. Part II

The first part of this review dealt with the physiology of glucose transport with specific emphasis on transporters of the brush border membrane (BBM) and the basolateral membrane (BLM). On the BBM, the sodium (Na)/glucose transporters (SGLT1 and SGLT2), the Na-independent transporter (GLUT5) and on the BLM the hexose transporter (GLUT2) are discussed. The molecular biology of these transporters is also reviewed. In the second part of the review, we discuss the manner in which intestinal adaptation may be modified by alterations in the diet, especially the lipid constituents, and two important examples of intestinal adaptation will be given: diabetes mellitus and inflammatory bowel disease.

Renal protein degradation in streptozotocin diabetic mice

In diabetes mellitus, the kidney and the gut--but not the liver or the muscle--undergo hypertrophy. Hypertrophy may be due to an increase in the rate of protein synthesis and/or to a decrease in proteolysis. In order to resolve this issue we assessed in vivo the rates of protein degradation by measuring the disappearance rates of 3H- and 14C-labelled valine incorporated into renal and liver proteins of control and streptozotocin-diabetic mice. The half-life of labelled valine, which is inversely related to the rate of protein degradation, was shorter and of similar magnitude both in the kidneys and livers of diabetic (70 +/- 6 h) than of control (96 +/- 8 h) animals. Yet, only the kidneys of diabetic animals underwent hypertrophy (0.33 +/- 0.01 vs. 0.29 +/- 0.01 g, P < 0.05; 2.22 +/- 0.10 vs. 1.64 +/- 0.05% of body weight, P < 0.01)). The increase in protein degradation rate affected all subcellular (mitochondrial, nuclear, microsomal and cytosolic) fractions of the kidney but not the mitochondria of liver. We surmise that an increase in the degradation of proteins is a widely generalized phenomenon in diabetes mellitus. For reasons that are still unclear, but that may relate to the hyperglycaemia, in the kidneys of diabetic animals this process is associated with a transiently larger increase in protein synthesis resulting in hypertrophy, whereas in liver, changes in protein degradation proceed 'pan passu' with those in protein synthesis resulting in the preservation of organ weight. Accelerated renal protein turnover and hypertrophy are early manifestations and perhaps harbingers of more severe renal changes in diabetes mellitus.

Nutritional and intestinal effects of the novel immunosuppressive agents: deoxyspergualin, rapamycin, and mycophenolate mofetil

OBJECTIVES

Transplantation of the small intestine would be an attractive therapeutic option for treatment of short bowel syndrome if effective, nontoxic immunosuppressive agents could be developed. This study examines the effect of three newly developed immuno-suppressive agents: rapamycin, deoxyspergualin, and mycophenolate mofetil, on the nutritional status and intestinal function of normal juvenile rats.

DESIGN & METHODS

Rapamycin (2 mg/kg every second day), deoxyspergualin (2 mg/kg every second day) and mycophenolate mofetil (MM) (25 mg/kg every second day) were injected subcutaneously for six weeks.

RESULTS

Rapamycin and deoxyspergualin caused significant reductions in weight gain without impairing feed intake. Both drugs caused small decreases in fat absorption; treatment with DSG induced an increase in permeability to 99Tc-DTPA. However, the permeability to other markers, such as mannitol and lactulose, was decreased in the rapamycin and mycophenolate mofetil-treated animals. Intestinal function in vitro was quantified using glucose flux (absorption). In the rapamycin group, there was a significant decrease in ileal uptake of glucose, with the net flux (absorption) being zero; there was an associated loss of villous size histologically. In the deoxyspergualin-treated groups, there was a decrease in the jejunal glucose flux. In the mycophenolate mofetil-treated animals, there was a decrease in jejunal with a compensatory increase in ileal glucose absorption. There were minor variations in intestinal morphology, but these were not consistent.

CONCLUSIONS

Rapamycin and deoxyspergualin in these doses cause a significant reduction in weight gain in healthy juvenile animals, and all the drugs caused changes in the active transport characteristics of the intestine. Accordingly, the use of these drugs for intestinal transplantation should be evaluated carefully for their nutritional impact.

Tacrolimus (FK506)--its effects on intestinal glucose transport

Tacrolimus (FK506) is at present the mainstay of immunosuppression for small intestinal transplantation. This study investigates the effects of chronic treatment with varying dosages of tacrolimus on animal well-being, weight gain, intestinal permeability, and the active transport of nutrients as measured by in vitro studies quantifying glucose flux. The effect of acute treatment with high-dose tacrolimus on glucose flux was also investigated. In the chronic studies, juvenile male Lewis rats were given tacrolimus in a dosage of 0.1 mg/kg, 0.5 mg/kg, and 2 mg/kg q. second day by subcutaneous injection for five weeks. In the acute studies, animals were treated with 2 mg/kg given q. 24 hr [mult] 48 hr, 24 hr and 12 hr prior to sacrifice. In the acute treatment groups, tacrolimus caused no change in glucose flux. In the chronically treated animals, FK506 levels were within the clinically relevant range. Chronic treatment with 0.5 and 2 mg/kg caused a significant reduction in weight gain. These same groups of animals had a significant increase in intestinal permeability as measured by absorption of 99Te-DTPA. Glucose flux was affected in all chronically treated groups, with net flux increasing in the jejunum and decreasing in the ileum. These findings show that chronic treatment with low-dose tacrolimus is well tolerated, but in higher doses there are significant effects in intestinal permeability and nutrient uptake, and animal weight gain. We suggest that these changes are due to alterations in intestinal permeability that do not appear to be mediated by an acute drug effect and more likely represent chronic changes, possibly from alterations in gene expression. These findings suggest that further studies regarding the effects of tacrolimus on nutrient transport, intestinal permeability, and the known immunologically related functions of tacrolimus should be done.

FK506 increases permeability in rat intestine by inhibiting mitochondrial function

BACKGROUND & AIMS

Under normal physiological conditions, the intestine presents an adenosine triphosphate (ATP)-dependent barrier to luminal contents. Disruption of this barrier function can occur when cellular metabolism is compromised. This study examined the effects of FK506 on intestinal permeability and enterocyte metabolic function in Lewis rats.

METHODS

Rats were administered FK506 at a dose of 0.1, 0.5, or 2 mg/kg on alternate days for 6 weeks. Intestinal permeability was assessed by measuring urinary recovery of 99mTc-diethylenetriamine pentacetate, and electrophysiological conductance measurements were performed in Ussing chambers. Metabolic function was assessed in isolated enterocytes by measuring total ATP and CO2 release from [14C]pyruvate and [14C]glucose.

RESULTS

Rats treated with FK506 showed a dose-dependent reduction in weight gain as well as increased in vivo and in vitro intestinal permeability. There was no difference in plasma creatinine or urinary output. Changes in permeability correlated with reduced ATP levels and CO2 release because of diminished mitochondrial function. Lactate production, as a measure of glycolytic activity, was not altered by FK506.

CONCLUSIONS

In a dose-dependent manner, FK506 treatment in rats reduces weight gain, increases intestinal permeability, and decreases the ability of the small intestine to use glucose as an energy source.

The effect of surgical bowel manipulation and anesthesia on intestinal glucose absorption in rats

The effects of surgical bowel manipulation and anesthesia on intestinal glucose absorption were determined in chronically catheterized rats. Total and passive rates of glucose absorption were measured using 3-O-methyl-glucose (3OMG) and L-glucose, metabolically inert analogues of D-glucose. The rates of 3OMG absorption immediately postoperative and 4 h later were 86 and 62% less than the absorption rate 6 d postoperative. The absorption rates of 3OMG 1 and 2 d postoperative were not different from 6 d postoperative. Absorption of L-glucose was not altered by bowel manipulation and anesthesia. Even after correction for the increased resistance of the unstirred water layer (UWL) after bowel manipulation, the rates of total and active intestinal glucose absorption immediately postoperative were only 11 and 15% of predicted rates of absorption. In chronically catheterized rats, > 75% of luminal 3OMG at a concentration of 400 mM was absorbed by active transport. The Km and Vmax of 3OMG active transport corrected for the resistance of the UWL were 11.3 mM and 15.6 mumoles/min, respectively. We conclude that measurements of intestinal glucose absorption performed within 24 h of surgical bowel manipulation greatly underestimate active absorption even if corrections are made to account for the increased resistance of the UWL.

Active transport of 3-O-methyl-glucose by the small intestine in chronically catheterized rats

A method is described for determining the fraction of intestinal 3-O-methyl-glucose (3OMG) absorption that occurs by active transport in chronically catheterized rats without the influence of anesthesia or surgical bowel manipulation. That fraction was determined by simultaneously measuring portal venous-aortic blood concentration gradients (delta C) of 3-O-methyl-glucose (3OMG) and L-glucose, metabolically inert analogues of D-glucose. 3OMG is actively and passively absorbed by the same mechanisms as D-glucose, L-glucose is only passively absorbed. The fraction of 3OMG that is actively transported was calculated from the difference between 3OMG and L-glucose absorption, divided by total 3OMG absorption. We found that more than 94% of 3-O-methyl-glucose is absorbed by active transport when luminal concentrations range from 50 to 400 mM. We conclude that in unrestrained, unanesthetized chronically catheterized rats, most 3OMG is actively absorbed by the intestine even at high luminal concentrations.

Vanadate treatment rapidly improves glucose transport and activates 6-phosphofructo-1-kinase in diabetic rat intestine

The effect of oral vanadate on intestinal sodium-dependent glucose transport and 6-phosphofructo-1-kinase (EC 2.7.1.11) activity was examined in male Sprague-Dawley rats following a 30-day period of non-treated streptozotocin-induced diabetes. Non-treated diabetic rats were hyperglycaemic and demonstrated increased intestinal sodium-dependent glucose transport and Na,K-ATPase activity compared with controls. These increases were associated with a significant decrease in the total activity and activity ratios (activity at 0.5 mmol/l fructose 6-phosphate at pH 7.0/activity at pH 8.0) of intestinal 6-phosphofructo-1-kinase and decreased levels of fructose 2,6-bisphosphate. Supplementation of drinking water with vanadate (0.5 mg/ml) resulted in a rapid decline in blood glucose levels to a slightly hyperglycaemic level. Jejunal glucose transport and Na,K-ATPase activity were normalized after 48 h of vanadate treatment. In contrast, ileal glucose transport was significantly reduced 12 h following beginning vanadate treatment even though Na,K-ATPase activity did not normalize until 36 h later. Km was significantly decreased in both jejunum and ileum by vanadate treatment indicating an increased affinity of the sodium-dependent intestinal glucose transporter for glucose. 6-phosphofructo-1-kinase total activity and susceptibility to ATP inhibition was completely restored after 12 h of vanadate treatment. This increase was associated with a rise in fructose 2,6-bisphosphate levels. Fasting rats for 12 h had no effect on glucose transport or 6-phosphofructo-1-kinase activity, indicating the anorectic effect of vanadate was not responsible for changes in either parameter. In contrast, cycloheximide prevented both the rise in 6-phosphofructo-1-kinase activity and the rise in fructose 2,6-bisphosphate levels, and the subsequent reduction in glucose transport, indicating a requirement for protein synthesis. The removal of vanadate resulted in an immediate return to pre-treatment blood glucose levels. In contrast, intestinal glucose transport and 6-phosphofructo-1-kinase activity remained at treatment levels up until 72 h, indicating that oral vanadate treatment can have prolonged beneficial effects on intestinal function. In conclusion, the treatment of streptozotocin-induced diabetic rats with oral vanadate results in an activation of 6-phosphofructo-1-kinase coupled with a normalization of intestinal sodium-dependent glucose transport. Vanadate may thus have a beneficial effect on intestinal function and may prove useful as oral adjunctive diabetic therapy.

Dietary omega 3 fatty acids and cholesterol modify enterocyte microsomal membrane phospholipids, cholesterol content and phospholipid enzyme activities in diabetic rats

Diabetes-associated changes in intestinal uptake of nutrients are modified by isocaloric variations in the type of dietary lipids, and are associated with alterations in the phospholipid and fatty acyl content of the intestinal brush border membrane. The present study was designed to test the hypothesis that diet- and diabetes-associated changes in enterocyte microsomal membrane phospholipids are due to variations in the activity of two phospholipid metabolizing enzymes, 1,2-diacylglycerol:CDPcholine cholinephosphotransferase (CPT) and phosphatidylethanolamine methyltransferase (PEMT). Adult female Wistar rats were fed one of four semisynthetic diets--beef tallow low in cholesterol (BT), beef tallow high in cholesterol (BTC), fish oil low in cholesterol (FO) or fish oil high in cholesterol. In half of the animals, diabetes mellitus was produced by injection of streptozotocin. Jejunal and ileal enterocyte microsomes (EMM) were isolated and analyzed for cholesterol and phospholipids, as well as for CPT and PEMT activities. In control animals, feeding FO reduced EMM total phospholipids including phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol. Feeding FO resulted in a greater than 95% reduction in the activity of CPT. Diabetes was associated with increased jejunal EMM total phospholipids including sphingomyelin (SM) and PE, without associated changes in CPT or PEMT. Dietary cholesterol supplementation did not affect EMM total cholesterol or phosphlipid composition in control rats fed BT or FO, but was associated with an increase in EMM cholesterol in diabetic rats fed BT or FO. A decrease in total phospholipids due to a decline in SM, PC and PE in diabetic rats fed FO was not associated with changes in the activities of CPT or PEMT in EMM.(ABSTRACT TRUNCATED AT 250 WORDS)

Na,K-ATPase in diabetic rat small intestine. Changes at protein and mRNA levels and role of glucagon

Na,K-ATPase activity and isoform expression were measured in rat small intestinal mucosa taken from both normal and streptozocin-treated diabetic rats. Enzyme activity and abundance was 1.7-2.3-fold higher in rats diabetic for 2 wk than in controls. This was associated with 1.4-1.7-fold increases in small intestinal protein and DNA content. Ouabain inhibition curves of Na,K-ATPase were monophasic with Kis of 2.6 +/- 1.4 x 10(-4) and 2.0 +/- 1.2 x 10(-4) M for control and diabetic rats, respectively (NS). Northern blot analysis revealed a 2.5-fold increase in mRNA alpha 1 and a 3.4-fold increase in mRNA beta 1 in diabetic rats relative to controls. Two thirds of this increase occurred within 24h after injection of streptozocin. Immunoblots of intestinal enzyme preparations from diabetic and control rats indicated the presence of alpha 1 and beta 1 subunits but not of alpha 2 or alpha 3. Administration of glucagon (80 micrograms/kg) to normal rats daily for 14-16 d increased mRNA alpha 1 3.1-fold but did not increase mRNA beta 1 or enzyme activity. In experimental diabetes, alpha 1 and beta 1 isoforms of Na,K-ATPase are coordinately upregulated at both protein and mRNA levels, an effect which appears to be partially mediated by the associated hyperglucagonemia.

Small intestine hexose transport in experimental diabetes. Increased transporter mRNA and protein expression in enterocytes

The effect of insulinopenic diabetes on the expression of glucose transporters in the small intestine was investigated. Enterocytes were sequentially isolated from jejunum and ileum of normal fed rats, streptozotocin-diabetic rats, and diabetic rats treated with insulin. Facilitative glucose transporter (GLUT) 2, GLUT5, and sodium-dependent glucose transporter 1 protein content was increased from 1.5- to 6-fold in enterocytes isolated from diabetic animals in both jejunum and ileum. Insulin was able to reverse the increase in transporter protein expression seen after induction of diabetes. There was a four- to eightfold increase in the amount of enterocyte glucose transporter mRNA after diabetes with greater changes in sodium-dependent glucose transporter 1 and GLUT2 than in GLUT5 levels. In situ hybridization showed that after the induction of diabetes there was new hybridization in lower villus and crypt enterocytes that was reversed by insulin treatment. Thus, the increase in total hexose transport caused by diabetes is due to a premature expression of hexose transporters by enterocytes along the crypt-villus axis, causing a cumulative increase in enterocyte transporter protein during maturation. These changes are likely to represent an adaptive response by the organism to increase nutrient absorption in a perceived state of tissue starvation. These adaptive changes may lead to exacerbation of hyperglycemia in uncontrolled diabetes.

Regulation of the ovine intestinal Na+/glucose co-transporter (SGLT1) is dissociated from mRNA abundance

We have investigated the mechanisms of regulation of the Na+/glucose co-transporter (SGLT1) in a ruminant animal, which is an exceptional model system for studying intestinal glucose transport. Pre-ruminant lambs absorb glucose, produced by hydrolysis of the milk sugar lactose, in the intestine via apical SGLT1 and basolateral facilitative glucose transporters (GLUT2). Weaning coincides with the development of the rumen, and consequently the amount of hexoses reaching the small intestine of the ruminant sheep is undetectable. During development, SGLT1 activity and abundance in intestinal brush-border membranes decreased by over 200-fold, and either maintaining lambs on a milk replacer diet or infusing sheep intestine with D-glucose restored co-transporter activity and expression. We have measured ovine intestinal SGLT1 mRNA levels during development, with changes in diet and after direct infusion of D-glucose or methyl alpha-D-glucopyranoside into the intestinal lumen, in order to determine the level of regulation. During development, mRNA levels decreased only 4-fold. Lambs maintained on a milk replacer diet showed no change in mRNA levels relative to age-matched controls. Finally, upon infusion of the intestine of the ruminant sheep with sugars, D-glucose infusion increased SGLT1 mRNA, but only by 2-fold, compared with a 60-90-fold increase in co-transporter number and activity. Since the change in Na(+)-dependent glucose transport activity is correlated with SGLT1 protein abundance, and since changes in mRNA levels do not account for the dramatic changes in protein abundance, we conclude that the principal level of SGLT1 regulation by luminal sugar is translational or post-translational.

Regional alterations in intestinal sucrase expression in streptozocin-treated chronically diabetic rats

In ad libitum-fed diabetic rats, sucrase specific activities in jejunum and ileum were significantly increased two- to threefold compared to controls, a response unaltered by pair-feeding. Gradients of sucrase activities along the ileal villus-to-crypt axis were readily measured in crypt regions in diabetic, but not in nondiabetic, rats. Changes in sucrase activities were commensurate with increases in sucrase immunoreactivity and not a result of altered functional activity. Insulin treatment reversed these effects, although insulin-deficiency, studied in food-deprived, nondiabetic rats, did not affect sucrase expression. We conclude that chronic diabetes significantly stimulates sucrase expression along the proximal-to-distal and villus-to-crypt axes of rat small intestine. In ileum, these changes suggest marked alterations in phenotypic development of enterocytes along the villus-to-crypt axis. Alterations in sucrase expression do not appear to correlate with insulin states and are not a consequence of altered functional activity.

The role of insulin in the intestinal absorption of glucose in the rat

1. Acute pre-treatment with either mannoheptulose or streptozotocin--both compounds acting as powerful suppressors of insulin secretion--caused a significant decrease on the in vivo rate of intestinal glucose absorption following an intragastric [U-14C]glucose administration. 2. Mannoheptulose treatment also lowered the rate of whole-body oxidation of the administered tracer. 3. Insulin had no effect on the metabolic fate of [U-14C]glucose by isolated enterocytes. 4. However, the rate of glucose uptake, measured by the oxidation of [1-14C]glucose to 14CO2 in the presence of phenazine methosulphate, was decreased by insulin at concentrations of 50-200 munits/ml. 5. In addition, the rate of transport of [U-14C]glucose by brush-border membrane vesicles was also inhibited by insulin at high concentrations (100-1000 munits/ml). 6. This indicated that insulin acts by inhibiting glucose transport in isolated in vitro preparations. 7. Acute pre-treatment with either mannoheptulose or streptozotocin caused a significant decrease in the rate of gastric emptying, measured as the distribution of [3H]insulin along the gastrointestinal tract, following an intragastric glucose load. 8. It is concluded that insulin secretion modulates intestinal glucose absorption in vivo by enhancing gastric emptying in spite of the inhibitory effects of glucose transport observed with in vitro preparations.

Diabetes and glucose transporter gene expression in rat small intestine

The expressions of Na(+)-dependent glucose transporter (SGLT1) and five facilitative glucose transporter genes (GLUT1-5) in the small intestine of streptozotocin (STZ)-induced diabetic rats were examined by RNA blotting analysis. The transcripts of SGLT1 mRNA gave bands of 4.5 Kilobases (Kb) and 2.8Kb (very faint band). The levels of SGLT1 mRNA were significantly increased in 30- and 60-day STZ rats, but not changed in acute diabetic rats (2- to 10- day STZ rats). The GLUT2 mRNA levels changed in parallel with the D-galactose transport activity, being increased about 4-fold in 5-day STZ rats. The transcripts of GLUT5 mRNA gave three bands of 5.1Kb, 2.8Kb and 2.OKb, whose levels were significantly reduced in 30- and 60-day STZ rats. These results suggest that the facilitative glucose transporter (GLUT2), in addition to the Na(+)-dependent glucose transporter (SGLT1), may play an important role in intestinal glucose transport in diabetic rats.

Feeding rats a diet enriched with saturated fatty acids prevents the inhibitory effects of acute and chronic ethanol exposure on the in vitro uptake of hexoses and lipids

Chow-fed rats were given 15% ethanol in their drinking water for 4 weeks, and then for the next 2 weeks of ethanol exposure they were fed isocaloric semisynthetic diets enriched in either saturated (S) or polyunsaturated (P, linoleic acid) fats. Food intake was lower in ethanol-fed (ETH) than in control (C) rats, but the average body weight gain was similar in ETH and C fed S or P. Intestinal dry weight and the percentage of the intestinal wall comprised of mucosa were more than 2-fold higher in ETH than C fed P, whereas these values were 50% lower in ETH than C fed S. The in vitro jejunal uptake of glucose and galactose was higher in ETH than C fed S, whereas the converse was true when feeding P. These effects were due to differences in the values of the maximal transport rate (Vmax), the Michaelis constant (Km), and the contribution of passive permeation. The relative permeability of the intestine to lipids was unchanged by giving ethanol or by feeding S or P, but the individual rates of uptake of most medium- and long-chain fatty acids and cholesterol were lower in ETH fed P as compared with S. In a second series of studies the acute effect of ethanol exposure was examined: animals were fed S or P for 2 weeks and the intestine was then removed: when 5% ethanol was added directly to the test solutions, there was lower in vitro jejunal and ileal uptake of glucose and higher jejunal uptake of 18:2 when rats were previously fed P, but not in those fed S. In summary; (1) feeding an isocaloric polyunsaturated fatty acid diet has a trophic effect on the intestinal mucosa of animals chronically drinking ethanol; and (2) feeding rats a diet enriched with saturated fatty acids prevents the inhibitory effects of acute and chronic ethanol exposure on the in vitro jejunal uptake of glucose, galactose and lipids observed in animals fed a polyunsaturated diet. Thus, the effect of chronic consumption of ethanol on the active and passive jejunal uptake of nutrients is influenced by the type of lipids in the animal's diet.

Diabetes mellitus and sugar transport across the brush-border and basolateral membranes of rat jejunal enterocytes

1. The effects of streptozotocin-induced diabetes mellitus on active jejunal glucose uptake in vivo, and on galactose movement across the brush-border (phlorhizin-sensitive) and basolateral (phlorhizin-insensitive) membranes of isolated upper and mid-villus enterocytes has been studied. 2. Chronic diabetes increased unidirectional phlorhizin-sensitive galactose uptake by mid-villus but not upper villus cells. In contrast, phlorhizin-insensitive uptake by both cell populations was enhanced by diabetes. 3. Diabetes increased glucose absorption in vivo by mechanisms which were unrelated to hyperphagia. Mucosal hyperplasia acting together with an epithelium containing a higher proportion of mature enterocytes is the most likely explanation for the response. 4. We conclude that, during diabetes, the mid-villus region is an important site of adaptation with functional changes occurring at both the brush-border and basolateral membranes. The increased hexose transport ability of the basolateral membrane is retained during cell transit along the villus.

Effect of chemically induced diabetes mellitus on glutamine transport in rat intestine

The effect of chemically induced diabetes mellitus on the intestinal transport of glutamine was examined using a brush-border membrane vesicle technique. Diabetes was induced by a single intraperitoneal injection of streptozotocin (100 mg/kg body weight). Control and diabetic rats were studied 5 days following the induction of diabetes. Na(+)-dependent and Na(+)-independent glutamine (0.5 mM) transport was found to be significantly higher in the diabetic rats than in the control rats. This increase was found to be caused by a significant increase in the Vmax of the Na(+)-dependent and the Na(+)-independent glutamine transport processes in the diabetic rats (Vmax of 3742 +/- 487 and 2055 +/- 279 pmol/mg protein per 7 s, respectively) compared with that of the control rats (2183 +/- 75 and 1271 +/- 83 pmol/mg protein per 7 s, respectively). The apparent Km values of glutamine transport systems, on the other hand, were similar in the two rat groups. Insulin treatment of the diabetic rats significantly reduced the Vmax of glutamine transport by both the Na(+)-dependent and the Na(+)-independent processes to a level similar to that of the control rats (Vmax in the insulin-treated diabetic rats of 2036 +/- 123 and 1247 +/- 105 pmol/mg protein per 7 s, respectively). This study demonstrates that chemically induced diabetes mellitus is associated with an increase in intestinal glutamine transport. This increase is the result of the diabetic condition itself and appears to be mediated through an increase in the number of the transport carriers of glutamine.

Induction of intestinal glucose carriers in streptozocin-treated chronically diabetic rats

The maximal transport capacity (Vmax) for intestinal glucose absorption is increased in experimentally induced chronic diabetes mellitus. Using [3H]phlorizin radioautography, we examined the relation between this increase in transport Vmax and the number and distribution of sodium-glucose co-transporters on the luminal surface of rat ileum. Male Lewis rats were made diabetic with streptozocin. Ninety days later we measured 3-O-methyl-D-glucopyranose absorption and specific [3H]phlorizin binding to the ileal mucosa of the same rats. Net 3-O-methyl-D-glucopyranose flux was 6.9-fold greater in diabetic rats compared with age-matched controls. Specific binding of [3H]phlorizin to the luminal surface was 7.2-fold greater in the diabetic rats. Radioautography revealed that, in chronic diabetes, specific phlorizin binding extends into the midvillus region of the ileum, whereas in age-matched controls, it is confined to villus tips. We believe that, in untreated diabetes, a larger fraction of intestinal villus epithelial cells participate in glucose absorption.

Paradoxical organ-specific adaptations to streptozotocin diabetes mellitus in adult rats

Adult male Fisher rats injected with streptozotocin (Stz) to produce diabetes mellitus demonstrated a significant loss of total body weight associated with adipose and muscle tissue wasting. Paradoxically, intestinal mass and length were increased in Stz-treated rats despite catabolism of other tissues. Concomitant with increased intestinal mass, food and water intake increased significantly in Stz-diabetic animals. Renal weight was not reduced despite the fall in total body weight. It is proposed that the adult Stz-diabetic rat responds to a loss of available insulin by polyphagia, polydipsia, and catabolism of adipose and muscle tissue and that a large percentage of available synthetic fuel is devoted to the production of additional intestinal tissue.