Nutrient Regulation of the Enteroinsular Axis And Insulin Secretion

Bone resorption and incretin hormones following glucose ingestion in healthy emerging adults

Background

Studies in adults indicate that macronutrient ingestion yields an acute anti-resorptive effect on bone, reflected by decreases in C-terminal telopeptide (CTX), a biomarker of bone resorption, and that gut-derived incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), facilitate this response. There remain knowledge gaps relating to other biomarkers of bone turnover, and whether gut-bone cross-talk is operative during the years surrounding peak bone strength attainment. This study first, describes changes in bone resorption during oral glucose tolerance testing (OGTT), and second, tests relationships between changes in incretins and bone biomarkers during OGTT and bone micro-structure.

Methods

We conducted a cross-sectional study in 10 healthy emerging adults ages 18-25 years. During a multi-sample 2-hour 75 g OGTT, glucose, insulin, GIP, GLP-1, CTX, bone-specific alkaline phosphatase (BSAP), osteocalcin, osteoprotegerin (OPG), receptor activator of nuclear factor kappa-β ligand (RANKL), sclerostin, and parathyroid hormone (PTH) were assayed at mins 0, 30, 60, and 120. Incremental areas under the curve (iAUC) were computed from mins 0-30 and mins 0-120. Tibia bone micro-structure was assessed using second generation high resolution peripheral quantitative computed tomography.

Results

During OGTT, glucose, insulin, GIP, and GLP-1 increased significantly. CTX at min 30, 60, and 120 was significantly lower than min 0, with a maximum decrease of about 53 % by min 120. Glucose-iAUC_0-30 inversely correlated with CTX-iAUC_0-120 (rho = -0.91, P < 0.001), and GLP-1-iAUC_0-30 positively correlated with BSAP-iAUC_0-120 (rho = 0.83, P = 0.005), RANKL-iAUC_0-120 (rho = 0.86, P = 0.007), and cortical volumetric bone mineral density (rho = 0.93, P < 0.001).

Conclusions

Glucose ingestion yields an anti-resorptive effect on bone metabolism during the years surrounding peak bone strength. Cross-talk between the gut and bone during this pivotal life stage requires further attention.

Endosomal trafficking in metabolic homeostasis and diseases

The global prevalences of obesity and type 2 diabetes mellitus have reached epidemic status, presenting a heavy burden on society. It is therefore essential to find novel mechanisms and targets that could be utilized in potential treatment strategies and, as such, intracellular membrane trafficking has re-emerged as a regulatory tool for controlling metabolic homeostasis. Membrane trafficking is an essential physiological process that is responsible for the sorting and distribution of signalling receptors, membrane transporters and hormones or other ligands between different intracellular compartments and the plasma membrane. Dysregulation of intracellular transport is associated with many human diseases, including cancer, neurodegeneration, immune deficiencies and metabolic diseases, such as type 2 diabetes mellitus and its associated complications. This Review focuses on the latest advances on the role of endosomal membrane trafficking in metabolic physiology and pathology in vivo, highlighting the importance of this research field in targeting metabolic diseases.

Effect of corn processing on growth performance, carcass characteristics, and plasma glucose-dependent insulinotropic polypeptide and metabolite concentrations in feedlot cattle

The objectives of this trial were to evaluate the association between corn processing, glucose-dependent insulinotropic polypeptide (GIP) concentration, and intramuscular (IM) fat deposition. We hypothesized that steers fed whole shelled corn (WSC) would have a greater IM fat deposition than steers fed cracked corn (CC) due to an increase in plasma GIP concentration. Backgrounded, Angus-cross cattle (initial body weight [BW] = 279 ± 9.8 kg) were used in a randomized complete block design in a feedlot setting for an average of 230 d. Cattle were allotted in 12 pens (6 pens per treatment with 8 animals per pen). There were three blocks: heifers (n = 32, initial BW = 265 ± 1.3 kg), small steers (n = 32, initial BW = 262 ± 1.3 kg), and large steers (n = 32, initial BW = 310 ± 1.4 kg). Two pens within each block were randomly assigned to one of the following treatments: 1) CC or 2) WSC. Animal growth performance, carcass characteristics, and plasma hormone and metabolite concentrations were analyzed using the MIXED procedure of SAS, including the fixed effects of treatment, or treatment, time, and their interaction. Pen and block were included as random effects. Carcass yield and quality grade distributions were compared using the GLIMMIX procedure of SAS. including the fixed effects of treatment and time with pen and block as random effects. Linear regression was used to evaluate the association of plasma GIP concentration and IM fat content. Average daily gain (P = 0.57) and final BW (P = 0.34) were similar, regardless of treatment. Cattle fed CC had reduced (P < 0.01) dry matter intake (DMI) when compared with those fed WSC. This lesser DMI resulted in improved gain:feed ratio (P < 0.01) for cattle fed CC compared with cattle fed WSC. There was no effect (P ≤ 0.33) of corn processing on plasma glucose, plasma GIP concentrations, hot carcass weight, dressing percentage, or marbling score. There was a positive linear relationship (P = 0.03) between IM fat concentration and plasma GIP concentration. In conclusion, feeding CC increased gain:feed ratio compared with WSC, but there was no difference in plasma GIP concentration, whereas plasma GIP concentration appears to be related to IM fat deposition.

Efficacy of fibre additions to flatbread flour mixes for reducing post-meal glucose and insulin responses in healthy Indian subjects

The incidence of type 2 diabetes mellitus (T2DM) is increasing worldwide, including in developing countries, particularly in South Asia. Intakes of foods generating a high postprandial glucose (PPG) response have been positively associated with T2DM. As part of efforts to identify effective and feasible strategies to reduce the glycaemic impact of carbohydrate-rich staples, we previously found that addition of guar gum (GG) and chickpea flour (CPF) to wheat flour could significantly reduce the PPG response to flatbread products. On the basis of the results of an exploratory study with Caucasian subjects, we have now tested the effect of additions of specific combinations of CPF with low doses of GG to a flatbread flour mix for their impacts on PPG and postprandial insulin (PPI) responses in a South-Asian population. In a randomised, placebo-controlled full-cross-over design, fifty-six healthy Indian adults consumed flatbreads made with a commercial flatbread mix (100 % wheat flour) with no further additions (control) or incorporating 15 % CPF in combination with 2, 3 or 4 % GG. The flatbreads with CPF and 3 or 4 % GG significantly reduced PPG (both ≥15 % reduction in positive incremental AUC, P<0·01) and PPI (both ≥28 % reduction in total AUC, P<0·0001) compared with flatbreads made from control flour. These results confirm the efficacy and feasibility of the addition of CPF with GG to flatbread flour mixes to achieve significant reductions in both PPG and PPI in Indian subjects.

Splanchnic metabolism of nutrients and hormones in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera1,2,3

Effects of increased ammonia and/or arginine absorption on net splanchnic (portal-drained viscera [PDV] plus liver) metabolism of nonnitrogenous nutrients and hormones in cattle were examined. Six Hereford x Angus steers (501 +/- 1 kg BW) prepared with vascular catheters for measurements of net flux across the splanchnic bed were fed a 75% alfalfa:25% (as-fed basis) corn and soybean meal diet (0.523 MJ of ME/[kg BW(0.75).d]) every 2 h without (27.0 g of N/kg of DM) and with 20 g of urea/kg of DM (35.7 g of N/kg of DM) in a split-plot design. Net flux measurements were made immediately before and after a 72-h mesenteric vein infusion of L-arginine (15 mmol/h). There were no treatment effects on PDV or hepatic O2 consumption. Dietary urea had no effect on splanchnic metabolism of glucose or L-lactate, but arginine infusion decreased net hepatic removal of L-lactate when urea was fed (P < 0.01). Net PDV appearance of n-butyrate was increased by arginine infusion (P < 0.07), and both dietary urea (P < 0.09) and arginine infusion (P < 0.05) increased net hepatic removal of n-butyrate. Dietary urea also increased total splanchnic acetate output (P < 0.06), tended to increase arterial glucagon concentration (P < 0.11), and decreased arterial ST concentration (P < 0.03). Arginine infusion increased arterial concentration (P < 0.07) and net PDV release (P < 0.10) and tended to increase hepatic removal (P < 0.11) of insulin, as well as arterial concentration (P < 0.01) and total splanchnic output (P < 0.01) of glucagon. Despite changes in splanchnic N metabolism, increased ammonia and arginine absorption had little measurable effect on splanchnic metabolism of glucose and other nonnitrogenous components of splanchnic energy metabolism.

Coffee acutely modifies gastrointestinal hormone secretion and glucose tolerance in humans: glycemic effects of chlorogenic acid and caffeine

BACKGROUND

Accumulating evidence suggests that certain dietary polyphenols have biological effects in the small intestine that alter the pattern of glucose uptake. Their effects, however, on glucose tolerance in humans are unknown.

OBJECTIVE

The objective was to investigate whether chlorogenic acids in coffee modulate glucose uptake and gastrointestinal hormone and insulin secretion in humans.

DESIGN

In a 3-way, randomized, crossover study, 9 healthy fasted volunteers consumed 25 g glucose in either 400 mL water (control) or 400 mL caffeinated or decaffeinated coffee (equivalent to 2.5 mmol chlorogenic acid/L). Blood samples were taken frequently over the following 3 h.

RESULTS

Glucose and insulin concentrations tended to be higher in the first 30 min after caffeinated coffee consumption than after consumption of decaffeinated coffee or the control (P < 0.05 for total and incremental area under the curve for glucose and insulin). Glucose-dependent insulinotropic polypeptide secretion decreased throughout the experimental period (P < 0.005), and glucagon-like peptide 1 secretion increased 0-120 min postprandially (P < 0.01) after decaffeinated coffee consumption compared with the control. Glucose and insulin profiles were consistent with the known metabolic effects of caffeine. However, the gastrointestinal hormone profiles were consistent with delayed intestinal glucose absorption.

CONCLUSIONS

Differences in plasma glucose, insulin, and gastrointestinal hormone profiles further confirm the potent biological action of caffeine and suggest that chlorogenic acid might have an antagonistic effect on glucose transport. Therefore, a novel function of some dietary phenols in humans may be to attenuate intestinal glucose absorption rates and shift the site of glucose absorption to more distal parts of the intestine.

Degradation, cyclic adenosine monophosphate production, insulin secretion, and glycemic effects of two novel N-terminal Ala2-substituted analogs of glucose-dependent insulinotropic polypeptide with preserved biological activity in vivo

Glucose-dependent insulinotropic polypeptide (GIP) has significant potential in diabetes therapy due to its ability to serve as a glucose-dependent activator of insulin secretion. However, its biological activity is severely compromised by the ubiquitous enzyme dipeptidylpeptidase IV (DPP IV), which removes the N-terminal Tyr(1)-Ala(2) dipeptide from GIP. Therefore, 2 novel N-terminal Ala(2)-substituted analogs of GIP, with Ala substituted by 2-aminobutyric acid (Abu) or sarcosine (Sar), were synthesized and tested for metabolic stability and biological activity both in vitro and in vivo. Incubation with DPP IV gave half-lives for degradation of native GIP, (Abu(2))GIP, and (Sar(2))GIP to be 2.3, 1.9, and 1.6 hours, respectively, while in human plasma, the half-lives were 6.2, 7.6, and 5.4 hours, respectively. In Chinese hamster lung (CHL) cells expressing the cloned human GIP receptor, native GIP, (Abu(2))GIP, and (Sar(2))GIP dose-dependently stimulated cyclic adenosine monophosphate (camp) production with EC(50) values of 18.2, 38.5, and 54.6 nmol/L, respectively. In BRIN-BD11 cells, both (Abu(2))GIP and (Sar(2))GIP (10(-13) to 10(-8) mol/L) dose-dependently stimulated insulin secretion with significantly enhanced effects at 16.7 mmol/L compared with 5.6 mmol/L glucose. In obese diabetic (ob/ob) mice, GIP and (Sar(2))GIP significantly increased (1.4-fold to 1.5-fold; P <.05) plasma insulin concentrations, whereas (Abu(2))GIP exerted only minor effects. Changes in plasma glucose were small reflecting the severe insulin resistance of this mutant. The present data show that substitution of the penultimate N-terminal Ala(2) in GIP by Abu or Sar results in analogs with moderately reduced metabolic stability and biological activity in vitro, but with preserved biological activity in vivo.

GIP biology and fat metabolism

The gastrointestinal hormone, gastric inhibitory polypeptide (GIP), is synthesized and released from the duodenum and proximal jejunum postprandially. Its release depends upon several factors including meal content and pre-existing health status (ie. obesity, diabetes, age, etc.). It was initially discovered and named for its gastric acid inhibitory properties. However, its more physiologically relevant role appears to be as an insulinotropic agent with a stimulatory effect on insulin release and synthesis. Accordingly, it was later renamed glucose-dependent insulinotropic polypeptide because its action on insulin release depends upon an increase in circulating levels of glucose. GIP is considered to be one of the principle incretin factors of the enteroinsular axis. The GIP receptor is a G-protein-coupled receptor belonging to the family of secretin/VIP receptors. GIP receptor mRNA is widely distributed in peripheral organs, including the pancreas, gut, adipose tissue, heart, adrenal cortex, and brain, suggesting it may have other functions in addition to the ones mentioned above. An overactive enteroinsular axis has been suggested to play a role in the pathogenesis of diabetes and obesity. In addition to stimulating insulin release, GIP has been shown to amplify the effect of insulin on target tissues. In adipose tissue, GIP has been reported to (1) stimulate fatty acid synthesis, (2) enhance insulin-stimulated incorporation of fatty acids into triglycerides, (3) increase insulin receptor affinity, and (4) increase sensitivity of insulin-stimulated glucose transport. In addition, although controversial, lipolytic properties of GIP have been proposed. The mechanism of action of GIP-induced effects on adipocytes is unknown, and it is unclear whether these effects of GIP on adipocytes are direct or indirect. However, there is now evidence that GIP receptors are expressed on adipocytes and that these receptors respond to GIP stimulation. Given the location of its release and the timing of its release, GIP is an ideal anabolic agent and expanding our understanding of its physiology will be needed to determine its exact role in the etiology of diabetes mellitus and obesity.

Differences in glucose-dependent insulinotrophic polypeptide hormone and hepatic lipase in subjects of southern and northern Europe: implications for postprandial lipemia

BACKGROUND

This study was an extension of a previous study that showed different lipemic responses to standard test meals in subjects from southern and northern Europe.

OBJECTIVE

The aim was to determine in 32 healthy young men from northern and southern Europe whether differences in the secretion of insulin and glucose-dependent insulinotrophic polypeptide (GIP) might explain these findings through the actions of these hormones on lipoprotein lipase.

DESIGN

We investigated in a randomized, single-blind, crossover study the effects of 2 test meals of identical macronutrient composition but different saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) contents on postprandial GIP, insulin, the ratio of incremental triacylglycerol to apolipoprotein B-48 (a marker of chylomicron size), and the activity of postheparin lipases.

RESULTS

Fasting and postprandial GIP concentrations and postheparin hepatic lipase activities were significantly higher in the southern Europeans (P < 0.001 and P < 0.02, respectively). Lipoprotein lipase activity after the SFA-rich meal was significantly higher in the northern Europeans (P < 0.01). HL activity 9 h after the SFA-rich meal and the area under the curve (AUC) for the postprandial insulin response correlated with the AUC for the postprandial GIP response [r = 0.44 (P < 0.04) and r = 0.46 (P < 0.05), respectively]. There were no significant differences in chylomicron size between the 2 groups for either meal, but when the groups were combined there was a significant difference in chylomicron size between the SFA- and MUFA-rich meals (P < 0.05), which could be due to the formation of larger chylomicrons after the MUFA-rich meal.

CONCLUSION

The significantly higher GIP and insulin responses and HL activities in southern Europeans may provide an explanation for our previous report of attenuated postprandial triacylglycerol and apolipoprotein B-48 responses in them.

Effect of gastric inhibitory polypeptide on bovine fat metabolism

Gastric inhibitory polypeptide (GIP), a hormone secreted by the gastrointestinal tract in response to nutrient absorption, exerts anabolic effects on adipose tissue in some species. Cattle fed on grass silage diets tend to deposit more fat than animals fed on dried forages. We investigated the effect of diet on blood GIP concentrations in cattle. Plasma concentrations tended to be higher in cattle fed grass silage alone or supplemented with fishmeal (0.61 ng/ml) compared with animals fed dried grass/barley (0.43 ng/ml, P > 0.1) and were inversely correlated with plasma insulin concentrations (r = -0.727, P < 0.01). The effects of increasing concentrations (0, 0.1, 1.0, 10.0 nM) of GIP and glucagon-like peptide-1 (GLP-1) on basal and insulin-stimulated lipogenesis in bovine adipose tissue in vitro were investigated after 4 and 24 h of incubation. No conclusive effects were obtained with either peptide. Subsequently, the effect of exogenous administration of GIP (10 or 50 ng/kg liveweight per min) on whole-body fat metabolism was investigated in two steers in vivo. Plasma concentration and flux rate of palmitate was increased by GIP only at the higher infusion level suggesting lipolysis and possibly fatty acid re-esterification was stimulated at high concentration. We conclude that although gut peptides may regulate nutrient utilisation, it is unlikely that they play a major role in promoting fat accretion in cattle. However, the small number of animals used in these studies indicates the need for caution and further studies are warranted.

Changes of plasma insulin, urea, amino acids and rumen metabolites in somatotropin treated dairy cows

An experiment was performed to evaluate the effects of somatotropin on plasma free amino acid, urea and insulin concentrations and rumen fermentation pattern and to assess their relationships. Four Italian Friesian dairy cows fitted with rumen cannulae were used in a switch-back design. Slow releasing recombinant bovine somatotropin (640 mg/cow) was injected every 28 days for two consecutive periods. Rumen fluid and blood samples were collected before and after feeding at 0, 7 and 21 days after rbST injection. Exogenous rbST increased plasma insulin concentration and the insulin response to feeding, and decreased plasma urea and free essential and branched chain amino acid concentrations. rbST did not affect rumen fermentation pattern. No correlation was found between rumen and plasma parameters measured after feeding. Our results are consistent with the notion that the main effect of somatotropin is post-absorptive.

Amino terminal glycation of gastric inhibitory polypeptide enhances its insulinotropic action on clonal pancreatic B-cells

Gastric inhibitory polypeptide (GIP) is a potent insulin-releasing hormone of the enteroinsular axis. This study has examined glycation of GIP and effects of such structural modification on insulin secretion from a glucose-responsive clonal pancreatic B-cell line (BRIN-BD11). Monoglycated GIP (Mr 5149.5) was prepared by incubation with d-glucose under reducing conditions and purified by HPLC. Automated Edman degradation and mass spectrometric analysis indicated that GIP was specifically glycated at the amino terminus. In acute (20 min) incubations at 5.6 mM glucose, GIP (3x10-11-10-8 M) significantly stimulated insulin secretion by 1.6-2.1-fold from BRIN-BD11 cells. The stimulatory effect induced by GIP over this concentration range was further enhanced by 1.5-2.5-fold following N-terminal glycation. These data indicate that GIP can be glycated under hyperglycaemic conditions at the amino terminal Tyr1, and that this modification increases the glucose-dependent insulinotropic action of the peptide.

The concentrations of some gut polypeptides are elevated during lactation in ruminants

Circulating concentrations of both glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1(7-36)amide (GLP-1) were determined in dry and lactating sheep. Both polypeptides were significantly higher in lactating animals compared with dry. The half-life of both in plasma was determined by intravenous injection of GIP or GLP-1 in both dry and lactating animals, but neither peptide showed a significantly different value during lactation. Thus, the increased circulating concentrations during lactation must result from increased secretion, probably resulting from the increased feed intake during lactation. Serum insulin concentrations were significantly lower during lactation, which poses the question of how lactating animals maintain lower circulating insulin levels in the presence of higher levels of insulinotropic agents.

A new breakfast cereal containing guar gum reduces postprandial plasma glucose and insulin concentrations in normal-weight human subjects

A new guar-containing wheatflake product was developed to assess its effect on carbohydrate tolerance in normal-weight, healthy subjects. The extruded wheatflake breakfast cereals containing 0 (control) or approximately 90 g guar gum/kg DM were fed to ten fasting, normal-weight, healthy subjects using a repeated measures design. The meals were similar in energy (approximately 1.8 MJ), available carbohydrate (78 g), protein (15 g) and fat (5.4 g) content. The guar gum content of the test meals was 6.3 g. Venous blood samples were taken fasting and at 15, 30, 45, 60, 90, 120, 150 and 240 min after commencing each breakfast and analysed for plasma glucose, insulin and C-peptide. The guar wheatflake meal produced a significant main effect for glucose and insulin at 0-60 min and 0-240 min time intervals respectively, but not for the C-peptide levels compared with the control meal. Significant reductions in postprandial glucose and insulin responses were seen following the guar wheatflake meal compared with the control meal at 15 and 60 min (glucose) and 15, 60, 90 and 120 min (insulin). The 60 and 120 min areas under the curve for glucose and insulin were significantly reduced by the guar gum meal, as was the 240 min area under the curve for insulin. Thus, it can be concluded that the use of a severe method of heat extrusion to produce guar wheatflakes does not diminish the physiological activity of the guar gum.

The effect of high-molecular-weight guar gum on net apparent glucose absorption and net apparent insulin and gastric inhibitory polypeptide production in the growing pig: relationship to rheological changes in jejunal digesta

The present study was designed to determine the quantitative effects of starchy meals containing guar gum on rates of net apparent glucose absorption and net apparent insulin and gastric inhibitory polypeptide (GIP) production in growing pigs. The effects of these meals on the viscosity of jejunal digesta were also examined and correlated to changes in glucose absorption. Four growing pigs were each given either a low-fat semi-purified diet (control) or the same diet supplemented with a high-molecular-weight guar gum at concentrations in the diet of 20 or 40 g/kg. Blood samples were removed simultaneously via indwelling catheters from the mesenteric artery and the hepatic portal vein. Samples of jejunal digesta were removed via a T-piece cannula and used immediately for viscosity measurements at 39 degrees. The 'zero-shear' viscosity of each sample was then calculated. Blood-flow measurements were made using an ultrasonic flow probe fitted to the hepatic portal vein. All measurements were made at intervals of 10 or 30 min during a 4 h postprandial period. Meals containing guar gum significantly increased (P < 0.05) the viscosity of jejunal digesta, an effect that was strongly dependent on the concentration of guar gum in the original diet. No significant differences in blood-flow rates were found between the control and guar-containing diets. Both concentrations of guar gum significantly reduced (P < 0.05) glucose absorption and insulin and GIP secretion rates over the 4 h postprandial period. An inverse relationship between the rate of glucose absorption and the 'zero-shear' viscosity of jejunal digesta was found. This study also provides direct evidence for the important role played by the enteroinsular axis in modifying the glycaemic response to a meal containing guar gum.

GIP and GLP-1(7-36)amide secretion in response to intraduodenal infusions of nutrients in pigs

Investigation of nutrient stimulation of two gut hormones GIP (glucose dependent insulotropic polypeptide) and GLP-1(7-36)amide (the active truncated form of glucagon-like peptide-1) is made difficult by the differential control of gastric emptying. Direct nutrient infusion into the duodenum was therefore carried out on three female pigs. The infusates consisted of saline (0.85 g or 1.7 g/100 ml); glucose (20 g or 40 g/100 ml); fat (30 g or 60 g/500 ml) and glucose/fat (20 g and 30 g or 40 g and 60 g per 1000 ml). Plasma glucose levels were elevated as expected by glucose or glucose/fat infusions, and they were not affected by the presence of fat in the infusate. Insulin secretion was stimulated in the presence of glucose or glucose/fat. Plasma triacylglycerol was elevated following fat and glucose/fat infusions. The greatest stimulus for GIP secretion was glucose/fat (P < 0.05); fat alone was a poor stimulus for GIP secretion, but glucose was a potent stimulus. GLP-1(7-36)amide was moderately stimulated by glucose and markedly stimulated by fat and glucose/fat infusions (P < 0.05). We conclude that, in pigs, dual nutrient infusion of glucose/fat is a strong stimulus for both GIP and GLP-1(7-36)amide secretion. The hormones therefore have the potential to play an important physiological role, both in the stimulation of insulin secretion and in adipose tissue metabolism in pigs.

Gastric inhibitory polypeptide concentrations in lambs fed milk or milk constituents

Gastric inhibitory polypeptide (GIP) concentrations were determined in plasma obtained from lambs before and after feeding milk or milk constituents. Plasma GIP increased after feeding whole milk or cream but was unchanged after the skimmed milk or lactose solution meal. Serum insulin concentrations increased after whole or skimmed milk or lactose solution was fed but were unchanged after the cream meal. Changes in plasma GIP concentrations correlated with changes in plasma triglycerides but not with plasma glucose or serum insulin. Triglyceride but not glucose absorption appears to be the stimulus for GIP secretion in lambs, and GIP does not appear to augment the glucose-induced secretion of insulin.

Blood glucose, plasma insulin and sensory responses to guar-containing wheat breads: effects of molecular weight and particle size of guar gum

The effectiveness of guar gum in reducing post-prandial blood glucose and plasma insulin levels in human subjects seems to depend mainly on its ability to increase the viscosity of digesta in the small intestine. However, the precise relationship between the rheological properties of guar gum (either in vitro or in vivo) and the changes in blood metabolites and hormones is unknown. The aim of the present study, therefore, was to investigate the effects of wheat breads containing guar gum samples varying in molecular weight (Mw) and particle size (characteristics that strongly influence the rheological properties of guar gum) on post-prandial blood glucose and plasma insulin levels in healthy subjects. The sensory qualities of breads containing guar-gum flours of different Mw were also evaluated using a hedonic scoring technique. No significant differences in the post-prandial blood glucose responses were found between the control and guar breads. However, all the guar breads elicited significant (P less than 0.05) decreases in the post-prandial rise in plasma insulin, an effect that did not appear to be influenced by large variations in Mw or particle size of guar gum. Moreover, the sensory qualities of guar bread were markedly improved by using low Mw grades of guar gum.

The effect of energy source and feeding level on the hormones of the entero-insular axis and plasma glucose in the growing pig

The aim of the experiment was to test the theory that accustoming pigs to a high-fat diet causes exaggerated gastric inhibitory polypeptide (GIP) secretion in response to a high-fat meal, and to determine whether hypersecretion of GIP could be related to an increase in the GIP content of the small intestine. Twenty-four pigs were fed one of three dietary regimens for 11 weeks: a high-carbohydrate diet (CL), or a high-fat diet (FL), both fed at 1.46 MJ gross energy (GE)/kg live weight0.75 per d, or a high-fat diet (FH) fed at 2.10 MJ GE/kg live weight0.75 per d. At the end of the period two acute tests were performed. For acute test 1 the accustomed meal (diets CL, FL and FH) and for acute test 2 a standard high-fat meal (diet FL) were given; blood samples were taken during the next 5 h and analysed for GIP, insulin and glucose. Integrated increases in hormone and glucose levels were compared by analysis of variance (0-300 min). In acute test 1 there were significantly different plasma GIP concentrations between groups (CL greater than FH greater than FL; P less than 0.05). Plasma insulin concentrations were significantly higher in group CL compared with groups FL and FH (P less than 0.002). There were no differences in glucose levels. In acute test 2 integrated increases in plasma GIP (0-300 min) concentrations were not significantly different; however, GIP (0-45 min) concentrations were significantly higher in group FH than in groups CL and FL (P less than 0.05). There were no differences in plasma insulin concentrations. Plasma glucose (0-300 min) concentrations were significantly higher in groups FL and FH compared with group CL (P less than 0.05). The GIP content of tissue samples taken at the end of the experiment from the duodenum, jejunum, upper and lower ileum decreased significantly in a proximal to distal direction (P less than 0.001). Diet FH significantly increased the average GIP content of the small intestine compared with diets CL and FL (P less than 0.05). It is concluded that fat meal-stimulated GIP secretion was enhanced by increased feeding level during a pre-treatment phase, possibly due to an increase in GIP synthesis in the small intestine. The high-fat diet caused glucose intolerance after a high-fat meal. This may be due in part to the action of dietary fat on glucose transport and metabolism.