Concurrent duodenal manometric and impedance recording to evaluate the effects of hyoscine on motility and flow events, glucose absorption, and incretin release

Upper gastrointestinal motor function and incretin hormone secretion are major determinants of postprandial glycemia and insulinemia. However, the impact of small intestinal flow events on glucose absorption and incretin release is poorly defined. Intraluminal impedance monitoring is a novel technique that allows flow events to be quantified. Eight healthy volunteers were studied twice, in random order. A catheter incorporating six pairs of electrodes at 3-cm intervals, and six corresponding manometry sideholes, was positioned in the duodenum. Hyoscine butylbromide (20 mg) or saline was given as an intravenous bolus, followed by a continuous intravenous infusion of either hyoscine (20 mg/h) or saline over 60 min. Concurrently, glucose and 3-O-methylglucose (3-OMG) were infused into the proximal duodenum (3 kcal/min), with frequent blood sampling to measure glucose, 3-OMG, insulin, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). The frequency of duodenal pressure waves and propagated pressure wave sequences was reduced by hyoscine in the first 10 min (P<0.01 for both), but not after that time. In contrast, there were markedly fewer duodenal flow events throughout 60 min with hyoscine (P<0.005). Overall, blood glucose (P<0.01) and plasma 3-OMG concentrations (P<0.05) were lower during hyoscine than saline, whereas plasma insulin, GLP-1, and GIP concentrations were initially (t=20 min) lower during hyoscine (P<0.05). In conclusion, intraluminal impedance measurement may be more sensitive than manometry in demonstrating alterations in duodenal motor function. A reduction in the frequency of duodenal flow events is associated with a decreased rate of glucose absorption and incretin release in healthy subjects.     

Pressure-geometry relationship in the antroduodenal region in humans

Understanding of the control mechanisms underlying gastric motor function is still limited. The aim of the present study was to evaluate antral pressure-geometry relationships during gastric emptying slowed by intraduodenal nutrient infusion and enhanced by erythromycin. In seven healthy subjects, antral contractile activity was assessed by combined dynamic magnetic resonance imaging and antroduodenal high-resolution manometry. After intragastric administration of a 20% glucose solution (750 ml), gastric motility and emptying were recorded during intraduodenal nutrient infusion alone and, subsequently, combined with intravenous erythromycin. Before erythromycin, contraction waves were antegrade (propagation speed: 2.7 +/- 1.7 mm/s; lumen occlusion: 47 +/- 14%). Eighty-two percent (51/62) of contraction waves were detected manometrically. Fifty-four percent of contractile events (254/473) were associated with a detectable pressure event. Pressure and the degree of lumen occlusion were only weakly correlated (r(2) = 0.02; P = 0.026). After erythromycin, episodes of strong antroduodenal contractions were observed. In conclusion, antral contractions alone do not reliably predict gastric emptying. Erythromycin induces strong antroduodenal contractions not necessarily associated with fast emptying. Finally, manometry reliably detects ~80% of contraction waves, but conclusions from manometry regarding actual contractile activity must be made with care.     

Glucagon-like peptide-2 protects against TPN-induced intestinal hexose malabsorption in enterally refed piglets

Premature infants receiving chronic total parenteral nutrition (TPN) due to feeding intolerance develop intestinal atrophy and reduced nutrient absorption. Although providing the intestinal trophic hormone glucagon-like peptide-2 (GLP-2) during chronic TPN improves intestinal growth and morphology, it is uncertain whether GLP-2 enhances absorptive function. We placed catheters in the carotid artery, jugular and portal veins, duodenum, and a portal vein flow probe in piglets before providing either enteral formula (ENT), TPN or a coinfusion of TPN plus GLP-2 for 6 days. On postoperative day 7, all piglets were fed enterally and digestive functions were evaluated in vivo using dual infusion of enteral ((13)C) and intravenous ((2)H) glucose, in vitro by measuring mucosal lactase activity and rates of apical glucose transport, and by assessing the abundances of sodium glucose transporter-1 (SGLT-1) and glucose transporter-2 (GLUT2). Both ENT and GLP-2 pigs had larger intestine weights, longer villi, and higher lactose digestive capacity and in vivo net glucose and galactose absorption compared with TPN alone. These endpoints were similar in ENT and GLP-2 pigs except for a lower intestinal weight and net glucose absorption in GLP-2 compared with ENT pigs. The enhanced hexose absorption in GLP-2 compared with TPN pigs corresponded with higher lactose digestive and apical glucose transport capacities, increased abundance of SGLT-1, but not GLUT-2, and lower intestinal metabolism of [(13)C]glucose to [(13)C]lactate. Our findings indicate that GLP-2 treatment during chronic TPN maintains intestinal structure and lactose digestive and hexose absorptive capacities, reduces intestinal hexose metabolism, and may facilitate the transition to enteral feeding in TPN-fed infants.     

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

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

Sympathetic neural responses to increased osmolality in humans

The purpose of this study was to examine the relationship between osmolality and efferent sympathetic outflow in humans. We hypothesized that increased plasma osmolality would be associated with increases in directly measured sympathetic outflow. Muscle sympathetic outflow was successfully recorded in eight healthy subjects during a 60-min intravenous hypertonic saline infusion (HSI; 3% NaCl) on one day and during a 60-min intravenous isotonic saline (ISO) infusion (0.9% NaCl) on a different day. The HSI provides an osmotic and volume stimulus, whereas the ISO infusion provides a volume-only stimulus. Muscle sympathetic nerve activity was quantified using the technique of peroneal microneurography. Plasma osmolality increased during the HSI but not during the ISO infusion (ANOVA, P < 0.05). Sympathetic outflow differed between the trials (ANOVA, P < 0.05); during the HSI burst, frequency initially increased from 14.6 +/- 2.5 to 18.1 +/- 1.9 bursts/min; during the ISO infusion, burst frequency initially declined from 14.7 +/- 2.5 to 12.0 +/- 2.1 bursts/min. Plasma norepinephrine concentration was greater at the end of the HSI compared with the end of the ISO infusion (HSI: 297 +/- 64 vs. ISO: 202 +/- 49 pg/ml; ANOVA, P < 0.05). We conclude that HSI-induced increases in plasma osmolality are associated with increases in sympathetic activity in humans.     

Effect of ethanol on intestinal lipid absorption in the rat

The effect of ethanol infusion on intestinal lipid absorption was studied in rats with a duodenal cannula. Rats were infused with ethanol overnight and ethanol was included in a trioleoylglycerol emulsion infusion given for 3 hr the next day. These rats were compared to control animals infused with glucose (isocalorically). The ethanol-infused rats had a greatly impaired lipid absorptive capacity. The monoacylglycerol and free fatty acid contents in the intestinal lumen in the ethanol-infused rats were 4- and 7-fold greater, respectively, than controls. The inhibition of absorption was not due to an effect of ethanol on lipolytic activity. The lipase content of the ethanol-infused rats was greater than controls and the separate infusion of monoacylglycerol and fatty acids demonstrated impaired absorption of these end products of lipolysis as compared to controls. To observe if these changes were due to an effect of ethanol on the enterocyte brush border membrane, the membrane lipids were analyzed. The phosphatidylcholine, lysophosphatidylcholine, and phosphatidylethanolanine content was reduced but not the neutral lipids, sphingomyelin, or phosphatidylserine. The uptake of fatty acid into intestinal rings was also shown to be impaired by ethanol infusion. Lastly, the specific activity of the neutral lipids remaining in the intestinal lumen after [3H]glycerol-labeled trioleoylglycerol-infusion was similar to controls even though the mass was much greater. It is concluded that ethanol impairs neutral lipid absorption due to an effect on the enterocyte brush border membrane and by increasing the efflux of low specific activity lipid from the enterocyte back out into the intestinal lumen. A potential pathway for this efflux is the recently described increased porosity of the apical junctional complex in response to ethanol infusion.     

GLP-1 reduces intestinal lymph flow, triglyceride absorption, and apolipoprotein production in rats

Glucagon-like peptide 1 (GLP-1) is a gastrointestinal hormone secreted in response to meal ingestion by enteroendocrine L cells located predominantly in the lower small intestine and large intestine. GLP-1 inhibits the secretion and motility of the upper gut and has been suggested to play a role in the "ileal brake." In this study, we investigated the effect of recombinant GLP-1-(7-36) amide (rGLP-1) on lipid absorption in the small intestine in intestinal lymph duct-cannulated rats. In addition, the effects of rGLP-1 on intestinal production of apolipoprotein (apo) B and apo A-IV, two apolipoproteins closely related to lipid absorption, were evaluated. rGLP-1 was infused through the jugular vein, and lipids were infused simultaneously through a duodenal cannula. Our results showed that infusion of rGLP-1 at 20 pmol.kg(-1).min(-1) caused a dramatic and prompt decrease in lymph flow from 2.22 +/- 0.15 (SE) ml/h at baseline (n = 6) to 1.24 +/- 0.06 ml/h at 2 h (P < 0.001). In contrast, a significant increase in lymph flow was observed in the saline (control) group: 2.19 +/- 0.20 and 3.48 +/- 0.09 ml/h at baseline and at 6 h of lipid infusion, respectively (P < 0.001). rGLP-1 also inhibited intestinal triolein absorption (P < 0.05) and lymphatic apo B and apo A-IV output (P < 0.05) but did not affect cholesterol absorption. In conclusion, rGLP-1 dramatically decreases intestinal lymph flow and reduces triglyceride absorption and apo B and apo A-IV production. These findings suggest a novel role for GLP-1 in lipid absorption.     

Lactose maldigestion during methotrexate-induced gastrointestinal mucositis in a rat model

Patients with chemotherapy-induced gastrointestinal mucositis suffer from anorexia, diarrhea, and stomach pain, often causing weight loss and malnutrition. When the intestinal function during mucositis would be known, a rational feeding strategy might improve the nutritional state, accelerate recuperation, and increase survival of mucositis patients. We developed a methotrexate (MTX)-induced mucositis rat model to study nutrient digestion and absorption. To determine lactose digestion and absorption of its derivative glucose during mucositis, we injected Wistar rats intravenously with MTX (60 mg/kg) or 0.9% NaCl (controls). Four days later, we orally administered trace amounts of [1-(13)C]lactose and [U-(13)C]glucose and quantified the appearance of labeled glucose in the blood for 3 h. Finally, we determined plasma citrulline level and harvested the small intestine to assess histology, myeloperoxidase level, glycohydrolase activity, immunohistochemical protein, and mRNA expression. MTX-treated rats showed profound villus atrophy and epithelial damage. During the experimental period, the absorption of lactose-derived [1-(13)C]glucose was 4.2-fold decreased in MTX-treated rats compared with controls (P < 0.01). Lactose-derived [1-(13)C]glucose absorption correlated strongly with villus length (rho = 0.86, P < 0.001) and with plasma citrulline level (rho = 0.81, P < 0.001). MTX treatment decreased jejunal lactase activity (19.5-fold, P < 0.01) and immunohistochemical protein and mRNA expression (39.7-fold, P < 0.01) compared with controls. Interestingly, MTX treatment did not affect the absorption of [U-(13)C]glucose during the experimental period. We conclude that lactose digestion is severely decreased during mucositis while glucose absorption is still intact, when supplied in trace amounts. Plasma citrulline level might be a useful objective, noninvasive marker for lactose maldigestion during mucositis in clinic.     

Effects of moderate hyperthyroidism and time relative to feeding on tissue responsiveness to insulin in sheep

The effects of moderate hyperthyroidism and time relative to feeding on tissue responsiveness to insulin were determined in four sheep using a hyperinsulinemic euglycemic clamp procedure, because thyroid hormones have glucoregulatory function in ruminants and non-ruminant animals. The sheep were fed alfalfa hay cubes and corn-based concentrates. They were intravenously injected in turn with saline (control treatment) and then with triiodothyronine (1.5 nmol d(-1); T3 treatment) once daily for 23 days for each treatment. The glucose clamp procedure was performed at four different times relative to feeding (before, during and after feeding) in both treatments. Insulin was intravenously infused at a constant rate of 6.0 mU (kgxmin)(-1) for 2 h and a glucose solution was infused to maintain euglycemia. Plasma T3 concentrations were higher (P=0.0001) for the T3 treatment than for the control treatment (4.0 and 1.3 nmol l(-1), respectively). For the glucose clamp procedure, glucose infusion rates were greater (P=0.0001) for the T3 treatment than for the control treatment, and were greater (P<0.05) during feeding than before feeding and after the end of feeding, but no interaction was detected. In conclusion, tissue responsiveness to insulin in sheep was independently enhanced by moderate hyperthyroidism induced by intravenous T3 injection and feeding.     

Rat small intestinal transit is independent of glucose consumption in the strenuous exercise

The present study was to determine the effect of strenuous exercise on glucose utilization, lactate accumulation and small intestinal transit (SIT). In strenuous exercises, rats would be put on the runway of a moving treadmill for a one-hour compulsive running. Rats first performed running treadmill for 45 min. After orogastric feeding of radiochromium marker, they resumed running for additional 15 min until sacrifice to measure SIT. Saline and various doses of glucose and lactate were infused through previously placed jugular vein during the whole procedure. Blood was finally obtained to measure plasma glucose and lactate levels. Saline infusion had no effect on running rat SIT during strenuous exercise, but plasma glucose level was significantly lowered (P < 0.01). Infusion of various doses of glucose did not alter SIT during strenuous exercise; however, the initially lowered plasma glucose was restored even to a hyperglycemic state. Meanwhile, strenuous running markedly increased plasma lactate level, irrespectively of saline or glucose infusion (P < 0.01). Lactate infusion did not change rat SIT obtained on the quiet runways. In conclusion, rat SIT remained unchanged in the strenuous exercise although obvious hypoglycemia and higher plasma lactate level did exist. Glucose utilization and lactate accumulation after the strenuous exercise may not directly mediate small intestinal motility.     

Regulation of intestinal and hypothalamic apolipoprotein A-IV

This review discusses the regulation of the intestinal and hypothalamic apolipoprotein A-IV (apo A-IV) gene and protein expression. Apo A-IV is a glycoprotein secreted together with triglyceride-rich lipoproteins by the small intestine. Intestinal apo A-IV synthesis is stimulated by fat absorption, probably mediated by chylomicron formation. This stimulation of intestinal apo A-IV synthesis is attenuated by intravenous leptin infusion. Chronic ingestion of a high-fat diet blunts the intestinal apo A-IV in response to dietary lipid. Intestinal apo A-IV synthesis is also stimulated by members of the pancreatic polypeptide family, including peptide YY (PYY), neuropeptide Y (NPY), and pancreatic polypeptide (PP). Recently, apo A-IV was demonstrated to be present in the hypothalamus as well. Hypothalamic apo A-IV level was reduced by food deprivation and restored by lipid feeding. Intracerebroventricular administration of apo A-IV antiserum stimulated feeding and decreased the hypothalamic apo A-IV mRNA level, implying that feeding is intimately regulated by endogenous hypothalamic apo A-IV. Central administration of NPY significantly increased hypothalamic apo A-IV mRNA levels in a dose-dependent manner.     

Acute and chronic increases in osmolality increase excitatory amino acid drive of the rostral ventrolateral medulla in rats

Water deprivation is associated with increased excitatory amino acid (EAA) drive of the rostral ventrolateral medulla (RVLM), but the mechanism is unknown. This study tested the hypotheses that the increased EAA activity is mediated by decreased blood volume and/or increased osmolality. This was first tested in urethane-anesthetized rats by determining whether bilateral microinjection of kynurenate (KYN, 2.7 nmol) into the RVLM decreases arterial pressure less in water-deprived rats after normalization of blood volume by intravenous infusion of isotonic saline or after normalization of plasma osmolality by intravenous infusion of 5% dextrose in water (5DW). Water-deprived rats exhibited decreased plasma volume and elevated plasma osmolality, hematocrit, and plasma sodium, chloride, and protein levels (all P < 0.05). KYN microinjection decreased arterial pressure by 24 +/- 2 mmHg (P < 0.05; n = 17). The depressor response was not altered following isotonic saline infusion but, while still present (P < 0.05), was reduced (P < 0.05) to -13 +/- 2 mmHg soon after 5DW infusion. These data suggest that the high osmolality, but not low blood volume, contributes to the KYN depressor response. To further investigate the action of increased osmolality on EAA input to RVLM, water-replete rats were also studied after hypertonic saline infusion. Whereas KYN microinjection did not decrease pressure immediately following the infusion, a depressor response gradually developed over the next 3 h. Lumbar sympathetic nerve activity also gradually increased to up to 167 +/- 19% of control (P < 0.05) 3 h after hypertonic saline infusion. In conclusion, acute and chronic increases in osmolality appear to increase EAA drive of the RVLM.     

Serum glucose and free fatty acids modulate growth hormone and luteinizing hormone secretion in the pig

Two experiments were conducted to determine the effect of free fatty acids (FFA) and glucose treatment on growth hormone (GH) and luteinizing hormone secretion in the pig. In Experiment (Exp) 1, 15 prepuberal gilts received an intravenous infusion of FFA (n = 5; 3 ml of 10% Liposyn II/kg), glucose (n = 5; 1 g/kg), or saline (n = 5; 3 ml of 0.9%/kg). Jugular blood samples were collected every 15 min for 2 hr before and 3 hr after intravenous infusion of saline, FFA, and glucose. Synthetic [Ala15]-h growth hormone-releasing factor-(1-29)NH2 (1 microgram/kg) and gonadotropin-releasing hormone (0.2 micrograms/kg) were administered 30 min after infusion (Time 0 = infusion). In Exp 2, eight prepuberal gilts received either FFA (n = 4) or saline (n = 4) as described in Exp 1, except that treatments were given every hour ove a 10-hr period. Blood samples were collected every 15 min from 1 hr before to 10 hr after the start of FFA or saline infusion. In Exp 1, the peak GH response to growth hormone-releasing factor was delayed by 45 min (P less than 0.01) by glucose treatment and suppressed (P less than 0.01) by FFA treatment. The luteinizing hormone response to gonadotroph-releasing hormone was suppressed (P less than 0.03) by glucose and enhanced (P less than 0.03) by FFA. In Exp 2, the number of GH pulses was increased (P less than 0.05) by FFA infusion and GH concentrations were positively correlated (r = 0.58, P less than 0.0003) with FFA concentrations, while luteinizing hormone pulse amplitude was greater (P less than 0.01) in FFA gilts than in saline gilts. These results indicate that FFA are more effective modulators of GH secretion than acute hyperglycemia, while metabolic status can alter pituitary responsiveness to gonadotropin-releasing hormone.     

Exendin-4 reduces fasting and postprandial glucose and decreases energy intake in healthy volunteers

Exendin-4 is a long-acting potent agonist of the glucagon-like peptide 1 (GLP-1) receptor and may be useful in the treatment of type 2 diabetes and obesity. We examined the effects of an intravenous infusion of exendin-4 (0.05 pmol. kg(-1). min(-1)) compared with a control saline infusion in healthy volunteers. Exendin-4 reduced fasting plasma glucose levels and reduced the peak change of postprandial glucose from baseline (exendin-4, 1.5 +/- 0.3 vs. saline, 2.2 +/- 0.3 mmol/l, P < 0.05). Gastric emptying was delayed, as measured by the paracetamol absorption method. Volunteers consumed 19% fewer calories at a free-choice buffet lunch with exendin-4 (exendin-4, 867 +/- 79 vs. saline 1,075 +/- 93 kcal, P = 0.012), without reported side effects. Thus our results are in accord with the possibility that exendin-4 may be a potential treatment for type 2 diabetes, particularly for obese patients, because it acts to reduce plasma glucose at least partly by a delay in gastric emptying, as well as by reducing calorie intake.     

Modulation of intestinal protein synthesis and protease mRNA by luminal and systemic nutrients

Route of nutrient supply is important in regulation of intestinal protein metabolism, because total parenteral nutrition, compared with enteral feeding, leads to profound atrophy. Participation of the fractional rate of protein synthesis (Ks), their degradation in regulation of gut protein balance, and their possible modulation by specific nutrients are the focus of our work. We developed an in situ experimental system that allows controlled exposure of intestinal mucosa to nutrients systemically, luminally, or both. We examined the effects of systemic glucose and amino acid (AA) infusion in overnight-fasted piglets. Jejunal segments within each piglet were simultaneously, luminally perfused with solutions containing various AAs or glucose. Intravenous infusion of glucose increased mucosal Ks by 16% (P < 0.05), whereas intravenous infusion of AA had no effect on Ks. Systemic glucose infusion had no effect on mRNA levels for components of the ubiquitin-proteasome proteolytic pathway. However, levels of these mRNA were reduced by intravenous or luminal AA supply. This effect was greatest (-50%) when highest tissue concentrations of AAs were achieved by the simultaneous infusion of AA by both routes (P < 0.05). Our findings suggest that not only is the modulation of protein balance in the intestine in response to nutrients in part attributable to anabolic stimulation of protein synthesis initiated by the systemic appearance of glucose, but a fall in protein degradation is also a likely contributor. AAs appear to be a key factor required to reduce expression of genes connected with proteolysis.     

Effects of load, and duration, of duodenal lipid on antropyloroduodenal motility, plasma CCK and PYY, and energy intake in healthy men

Enterally administered lipid modulates antropyloroduodenal motility, gut hormone release, appetite, and energy intake. We hypothesized that these effects would be dependent on both the load, and duration, of small intestinal exposure to lipid. Eleven healthy men were studied on four occasions in a double-blind, randomized, fashion. Antropyloroduodenal motility, plasma CCK and peptide YY (PYY) concentrations, and appetite perceptions were measured during intraduodenal infusion of lipid (Intralipid) at 1) 1.33 kcal/min for 50 min, 2) 4 kcal/min for 50 min, and 3) 1.33 kcal/min for 150 min, or 4) saline for 150 min. Immediately after the infusions, energy intake was quantified. Pressure wave sequences (PWSs) were suppressed, and basal pyloric pressure, isolated pyloric pressure waves (IPPWs), plasma CCK and PYY stimulated (all P < 0.05), during the first 50 min of lipid infusion, in a load-dependent fashion. The effect of the 4 kcal/min infusion was sustained so that the suppression of antral pressure waves (PWs) and PWSs and increase in PYY remained evident after cessation of the infusion (all P < 0.05). The prolonged lipid infusion (1.33 kcal/min for 150 min) suppressed antral PWs, stimulated CCK and PYY and basal pyloric pressure (all P < 0.05), and tended to stimulate IPPWs when compared with saline throughout the entire infusion period. There was no significant effect of any of the lipid infusions on appetite or energy intake, although nausea was slightly higher (P < 0.05) with the 4 kcal/min infusion. In conclusion, both the load, and duration, of small intestinal lipid influence antropyloroduodenal motility and patterns of CCK and PYY release.     

Increased lactulose/rhamnose ratio during fluid load is caused by increased urinary lactulose excretion

Noninvasive assessment of intestinal permeability in vivo is based on the measurement of urinary excretion of orally administered sugar probes. It is expressed as a ratio, usually lactulose/rhamnose or 3-O-methyl-D-glucose (3-OMG)/rhamnose. In both endotoxemic and control rats that were receiving fluid, we observed an increase in the recovery of lactulose and 3-OMG but not rhamnose in both groups, suggesting an enhancement of intestinal permeability. In the measurement of intestinal permeability, all pre- and postmucosal factors are considered equal for all sugars. We hypothesized that postmucosal factors and not changes in intestinal permeability caused the increased urinary lactulose and 3-OMG recoveries observed during fluid loading. Therefore, the effects of fluid loading on urinary excretion of the sugar probes were studied in healthy rats receiving the sugars intravenously. After intravenous injection, fluid loading increased urinary lactulose recovery threefold but not that of 3-OMG and rhamnose. In conclusion, fluid loading increases the lactulose/rhamnose ratio independent of changes in intestinal permeability. The 3-OMG/rhamnose ratio is not influenced by fluid loading.     

Supplementation with L-Glutamine and L-Alanyl-L-Glutamine Changes Biochemical Parameters and Jejunum Morphophysiology in Type 1 Diabetic Wistar Rats

We evaluated the effects of the supplementation with L-glutamine and glutamine dipeptide (GDP) on biochemical and morphophysiological parameters in streptozotocin-diabetic rats. For this purpose, thirty animals were distributed into six groups treated orally (gavage) during thirty days: non diabetic rats (Control) + saline, diabetic + saline; Control + L-glutamine (248 mg/kg), Diabetic + L-glutamine (248 mg/kg), Control + GDP (400 mg/kg), Diabetic + GDP (400 mg/kg). Diabetes was induced by an intravenous injection of streptozotocin (60 mg/kg) and confirmed by fasting glucose ≥ 200 mg/dL. Physiological parameters, i.e., body mass, food intake, blood glucose, water intake, urine and faeces were evaluated during supplementation. After the period of supplementation, the animals were euthanized. The blood was collected for biochemical assays (fructosamine, transaminases, lipid profile, total protein, urea, ammonia). Moreover, the jejunum was excised and stored for morphophysiological assays (intestinal enzyme activity, intestinal wall morphology, crypt proliferative index, number of serotoninergic cells from the mucosa, and vipergic neurons from the submucosal tunica). The physiological parameters, protein metabolism and intestinal enzyme activity did not change with the supplementation with L-glutamine or GDP. In diabetic animals, transaminases and fructosamine improved with L-glutamine and GDP supplementations, while the lipid profile improved with L-glutamine. Furthermore, both forms of supplementation promoted changes in jejunal tunicas and wall morphometry of control and diabetic groups, but only L-glutamine promoted maintenance of serotoninergic cells and vipergic neurons populations. On the other hand, control animals showed changes that may indicate negative effects of L-glutamine. Thus, the supplementation with L-glutamine was more efficient for maintaining intestinal morphophysiology and the supplementation with GDP was more efficient to the organism as a whole. Thus, we can conclude that local differences in absorption and metabolism could explain the differences between the supplementation with L-glutamine or GDP.     

Simulation of shoot chloride accumulation: separation of physical and biochemical processes governing plant salt tolerance

The effect of growth under saline condition (100 mol m^-3 NaCl in the nutrient solution) on the influx and the efflux of glucose from roots of cotton plants was analysed utilising the non metabolisable glucose analogue [¹⁴C]-3-O-methylglucose ([¹⁴C]3-OMG). Apical segments (1 cm long) excised from cotton roots took up [¹⁴C]3-OMG. At each tested concentration (5–500 mmol m^-3), the influx was completely inhibited by the presence of the protonophore carbonylcyanide-m-chlorophenyl hydrazone (CCCP) indicating that it is mediated by a H⁺-coupled co-transport mechanism. The CCCP-sensitive [¹⁴C]3-OMG influx was lower in the root segments excised from plants grown on saline solution than in the controls, and this was particularly evident at lower external concentrations. This difference was not due to a lower H⁺ apoplastic availability. In fact, the saline condition did not affect the pH of the rhizosphere and indeed the H⁺–ATPase activity, evaluated in plasma membrane vesicles purified from saline-treated plants, was higher (+23%) than in the controls. The lower uptake of [¹⁴C]3-OMG into saline treated root segments was related to an enhanced value of the apparent K_m of the carrier for the glucose analogue. This effect is discussed in relation to either the more positive value of the transmembrane electric potential difference (ΔΨ) measured in these root segments, or a competitive inhibition of Na⁺ on the H⁺ binding site of the carrier. Growth in saline solution slightly affected the efflux of the [¹⁴C]3-OMG preloaded in root segments, changing the membrane permeability to the molecule. The results strongly suggest that the higher (2.5 fold) net exudation of glucose, observed in short-term (4 h) collection experiments, from roots of cotton plants grown in saline condition, is mainly due to an effect of the saline growth condition on the system involved in the reabsorption of the hexose rather than on its efflux. This revised version was published online in June 2006 with corrections to the Cover Date.     

Jejunal and cecal 3-oxy-methyl-D-glucose absorption in chicken using a perfusion system in vivo

3-oxy-methyl-D-glucose (3-OMG) absorption by jejunum and caecum has been studied in the domestic fowl in vivo, with luminal perfusion, during 5 min periods. The diffusion component was evaluated in the presence of phloridzin (10(-3) M) that inhibits the active transport mechanism. Kd of jejunal and cecal diffusion of the monosaccharide have been calculated, showing a similar value. The Kt and Vmax of 3-OMG absorption were calculated using a graphical method for the two intestinal segments. The caecum showed a lower Kt and Vmax than the jejunum did.