The Yucatan minipig model: A new preclinical model of malnutrition in obese patients with acute or chronic diseases

BACKGROUND & AIMS

Malnutrition can develop in patients with obesity suffering from acute or chronic illness or after obesity surgery, promoting sarcopenic obesity. A better understanding of this pathophysiology and the development of new therapeutics for chronic diseases, that are often complicated with malnutrition and obesity, justify the development of new animal experimental models close to the human physiology. This study aims to characterize the effects of obesity and underfeeding on Yucatan obese minipigs, assessing its validity as a preclinical model for obesity-related malnutrition.

METHODS

Sixteen 30-month-old Yucatan minipigs were divided into two groups for 8 weeks: a standard diet group (ST, n = 5) and an obesogenic diet group (OB, n = 11). After 8 weeks, the OB group was further divided into two sub-groups: a standard diet group (OB-ST, n = 5) and a low-calorie/low-protein diet group (OB-LC/LP, n = 6) for 8 weeks. Body composition by CT-Scan and blood parameters were monitored, and trapezius muscle biopsies were collected to analyse signaling pathways involved in protein turnover and energy metabolism.

RESULTS

At W8, OB-ST animals exhibited significantly higher body weight (+37.7%, p = 0.03), muscle mass (+24.9%, p = 0.02), and visceral fat (+192.0%, p = 0.03) compared to ST. Trapezius cross sectional area (CSA) normalized to body weight was lower in OB-ST animals (-15.02%, p = 0.017). At W16, no significant changes were observed in protein turnover markers, although REDD1 increased in OB-ST (96.4%, p = 0.02). After 8 weeks of low-caloric/low protein diet, OB-LC/LP showed decreased body weight (-9.8%, p = 0.03), muscle mass (-6.5%, p = 0.03), and visceral fat (-41.5%, p = 0.03) compared to OB-ST animals. Trapezius fiber CSA significantly decreased in OB-LC/LP (-36.1%, p < 0.0001) and normalized to body weight (-25.4%, p < 0.0001), combined to higher ubiquitinated protein content (+38.3%, p = 0.02).

CONCLUSION

Our data support that the Yucatan minipig model mimics nutritional and skeletal muscle phenotypes observed in obese patients, with or without protein-energy malnutrition. It also reproduces muscle atrophy observed in chronic diseases or post-obesity surgery, making it a promising preclinical model for obesity-related malnutrition.

Open-source 3D printable frameless stereotaxic system for young and adult pigs

BACKGROUND

Here we present an open-source solution, comprising several 3D-printable mechanical pieces and software tools, for frameless stereotaxic targeting in young and adult pigs of varying weights.

NEW METHOD

Localization was achieved using an IR camera and CT imaging. The positions of the tools were followed, after registration of the pig stereotaxic space, with a CT scan and open-source brain atlas. The system was used to target the lateral ventricle and the subthalamic nucleus (STN) in one piglet and two adult Yucatan miniature pigs, which were either normal weight or obese.

RESULTS AND CONCLUSIONS

Positive targeting was confirmed in the first trial for all subjects, either by radiopaque CT enhancement of the ventricle or actual recording of the STN electrophysiological signature. We conclude that open-source freely available models, easily built with low-end 3D printers, and their associated software can be effectively used for brain surgery in pigs, at a minimal cost, irrespective of the weight of the animal.

Vagally Mediated Gut-Brain Relationships in Appetite Control-Insights from Porcine Studies

Signals arising from the upper part of the gut are essential for the regulation of food intake, particularly satiation. This information is supplied to the brain partly by vagal nervous afferents. The porcine model, because of its sizeable gyrencephalic brain, omnivorous regimen, and comparative anatomy of the proximal part of the gut to that of humans, has provided several important insights relating to the relevance of vagally mediated gut-brain relationships to the regulation of food intake. Furthermore, its large size combined with the capacity to become obese while overeating a western diet makes it a pivotal addition to existing murine models, especially for translational studies relating to obesity. How gastric, proximal intestinal, and portal information relating to meal arrival and transit are encoded by vagal afferents and their further processing by primary and secondary brain projections are reviewed. Their peripheral and central plasticities in the context of obesity are emphasized. We also present recent insights derived from chronic stimulation of the abdominal vagi with specific reference to the modulation of mesolimbic structures and their role in the restoration of insulin sensitivity in the obese miniature pig model.

Acceleration of Gastric Emptying by Insulin-Induced Hypoglycemia is Dependent on the Degree of Hypoglycemia

CONTEXT

Hypoglycemia is a major barrier to optimal glycemic control in insulin-treated diabetes. Recent guidelines from the American Diabetes Association have subcategorized "non-severe" hypoglycemia into level 1 (<3.9 mmol/L) and 2 (<3 mmol/L) hypoglycemia. Gastric emptying of carbohydrate is a major determinant of postprandial glycemia but its role in hypoglycemia counter-regulation remains underappreciated. "Marked" hypoglycemia (~2.6 mmol/L) accelerates gastric emptying and increases carbohydrate absorption in health and type 1 diabetes, but the impact of "mild" hypoglycemia (3.0-3.9 mmol/L) is unknown.

OBJECTIVE

To determine the effects of 2 levels of hypoglycemia, 2.6 mmol/L ("marked") and 3.6 mmol/L ("mild"), on gastric emptying in health.

DESIGN, SETTING, AND SUBJECTS

Fourteen healthy male participants (mean age: 32.9 ± 8.3 years; body mass index: 24.5 ± 3.4 kg/m2) from the general community underwent measurement of gastric emptying of a radiolabeled solid meal (100 g beef) by scintigraphy over 120 minutes on 3 separate occasions, while blood glucose was maintained at either ~2.6 mmol/L, ~3.6 mmol/L, or ~6 mmol/L in random order from 15 minutes before until 60 minutes after meal ingestion using glucose-insulin clamp. Blood glucose was then maintained at 6 mmol/L from 60 to 120 minutes on all days.

RESULTS

Gastric emptying was accelerated during both mild (P = 0.011) and marked (P = 0.001) hypoglycemia when compared to euglycemia, and was more rapid during marked compared with mild hypoglycemia (P = 0.008). Hypoglycemia-induced gastric emptying acceleration during mild (r = 0.57, P = 0.030) and marked (r = 0.76, P = 0.0014) hypoglycemia was related to gastric emptying during euglycemia.

CONCLUSION

In health, acceleration of gastric emptying by insulin-induced hypoglycemia is dependent on the degree of hypoglycemia and baseline rate of emptying.

Contrasted central effects of n-3 versus n-6 diets on brain functions in diet-induced obesity in minipigs

INTRODUCTION

N3 polyunsaturated fatty acids (n-3 PUFAs) exert anti-inflammatory effects for the hypothalamus, but their extra-hypothalamic outcome lack documentation. We evaluated the central consequences of the substitution of saturated fatty acids with n-3 or n-6 PUFA in obesogenic diets.

METHODS

Twenty-one miniature pigs were fed ad libitum obesogenic diets enriched in fat provided either as lard, fish oil (source for n-3 PUFAs), or sunflower oil (source for n-6 PUFAs) for ten weeks. The blood-brain barrier (BBB) permeability was quantified by CT perfusion. Central autonomic network was evaluated using heart rate variability, and PET 18FDG was performed to assess brain metabolism.

RESULTS

BBB permeability was higher in lard group, but heart rate variability changed only in fish oil group. Brain connectivity analysis and voxel-based comparisons show regional differences between groups except for the cingulate cortex in fish oil vs. sunflower oil groups.

DISCUSSION

: The minute changes in brain metabolism in obese pigs feed with fish oil compared with saturated fatty acids were sufficient to induce detrimental changes in heart rate variability. On the contrary, the BBB's decreased permeability in n-3 and n-6 PUFAs groups was protective against an obesity-driven damaged BBB.

Glucose Sensing Mediated by Portal Glucagon-Like Peptide 1 Receptor Is Markedly Impaired in Insulin-Resistant Obese Animals

The glucose portal sensor informs the brain of changes in glucose inflow through vagal afferents that require an activated glucagon-like peptide 1 receptor (GLP-1r). The GLP-1 system is known to be impaired in insulin-resistant conditions, and we sought to understand the consequences of GLP-1 resistance on glucose portal signaling. GLP-1-dependent portal glucose signaling was identified, in vivo, using a novel ⁶⁸Ga-labeled GLP-1r positron-emitting probe that supplied a quantitative in situ tridimensional representation of the portal sensor with specific reference to the receptor density expressed in binding potential units. It also served as a map for single-neuron electrophysiology driven by an image-based abdominal navigation. We determined that in insulin-resistant animals, portal vagal afferents failed to inhibit their spiking activity during glucose infusion, a GLP-1r-dependent function. This reflected a reduction in portal GLP-1r binding potential, particularly between the splenic vein and the entrance of the liver. We propose that insulin resistance, through a reduction in GLP-1r density, leads to functional portal desensitization with a consequent suppression of vagal sensitivity to portal glucose.

Pancreatic GLP-1r binding potential is reduced in insulin-resistant pigs

INTRODUCTION

The insulinotropic capacity of exogenous glucagon like peptide-1 (GLP-1) is reduced in type 2 diabetes and the insulin-resistant obese. We have tested the hypothesis that this response is the consequence of a reduced pancreatic GLP-1 receptor (GLP-1r) density in insulin-resistant obese animals.

RESEARCH DESIGN AND METHODS

GLP-1r density was measured in lean and insulin-resistant adult miniature pigs after the administration of a ⁶⁸Ga-labeled GLP-1r agonist. The effect of hyperinsulinemia on GLP-1r was assessed using sequential positron emission tomography (PET), both in the fasted state and during a clamp. The impact of tissue perfusion, which could account for changes in GLP-1r agonist uptake, was also investigated using ⁶⁸Ga-DOTA imaging.

RESULTS

GLP-1r binding potential in the obese pancreas was reduced by 75% compared with lean animals. Similar reductions were evident for fat tissue, but not for the duodenum. In the lean group, induced hyperinsulinemia reduced pancreatic GLP-1r density to a level comparable with that of the obese group. The reduction in blood to tissue transfer of the GLP-1r ligand paralleled that of tissue perfusion estimated using ⁶⁸Ga-DOTA.

CONCLUSIONS

These observations establish that a reduction in abdominal tissue perfusion and a lower GLP-1r density account for the diminished insulinotropic effect of GLP-1 agonists in type 2 diabetes.

Disparities in gastric emptying and postprandial glycaemia between Han Chinese and Caucasians with type 2 diabetes

AIMS

Gastric emptying is a major determinant of postprandial glycaemia in both health and type 2 diabetes (T2DM); the potential impact of ethnicity on gastric emptying is unclear. We compared the rate of gastric emptying of a standardised meal and the associated glycaemic response in Han Chinese and Caucasian patients with T2DM.

METHODS

14 Han Chinese and 14 Caucasian T2DM patients, managed by diet and/or metformin monotherapy, underwent concurrent measurements of gastric emptying and blood glucose for 240 min after a 99mTc-calcium phytate-labelled mashed potato meal.

RESULTS

Han Chinese patients were slightly younger (P < 0.05), and had a lower BMI (P < 0.05), than Caucasians. There were no differences in either HbA1c or fasting blood glucose between them. Gastric half-emptying time (T50) was shorter (P < 0.05) and the postprandial blood glucose increment greater (P < 0.05) in Han Chinese than Caucasian patients. Both the increment in blood glucose from baseline at 60 min and peak blood glucose were related inversely to T50 (P < 0.05 each).

CONCLUSIONS

Han Chinese with relatively well-controlled T2DM have more rapid gastric emptying compared to Caucasians, which is associated with a greater postprandial glycaemic excursion. These differences may inform the choice of management, e.g. Han Chinese may particularly benefit from therapies that slow gastric emptying.

Low-calorie sweeteners augment tissue-specific insulin sensitivity in a large animal model of obesity

PURPOSES

Whether low-calorie sweeteners (LCS), such as sucralose and acesulfame K, can alter glucose metabolism is uncertain, particularly given the inconsistent observations relating to insulin resistance in recent human trials. We hypothesized that these discrepancies are accounted for by the surrogate tools used to evaluate insulin resistance and that PET ¹⁸FDG, given its capacity to quantify insulin sensitivity in individual organs, would be more sensitive in identifying changes in glucose metabolism. Accordingly, we performed a comprehensive evaluation of the effects of LCS on whole-body and organ-specific glucose uptake and insulin sensitivity in a large animal model of morbid obesity.

METHODS

Twenty mini-pigs with morbid obesity were fed an obesogenic diet enriched with LCS (sucralose 1 mg/kg/day and acesulfame K 0.5 mg/kg/day, LCS diet group), or without LCS (control group), for 3 months. Glucose uptake and insulin sensitivity were determined for the duodenum, liver, skeletal muscle, adipose tissue and brain using dynamic PET ¹⁸FDG scanning together with direct measurement of arterial input function. Body composition was also measured using CT imaging and energy metabolism quantified with indirect calorimetry.

RESULTS

The LCS diet increased subcutaneous abdominal fat by ≈ 20% without causing weight gain, and reduced insulin clearance by ≈ 40%, while whole-body glucose uptake and insulin sensitivity were unchanged. In contrast, glucose uptake in the duodenum, liver and brain increased by 57, 66 and 29% relative to the control diet group (P < 0.05 for all), while insulin sensitivity increased by 53, 55 and 28% (P < 0.05 for all), respectively. In the brain, glucose uptake increased significantly only in the frontal cortex, associated with improved metabolic connectivity towards the hippocampus and the amygdala.

CONCLUSIONS

In miniature pigs, the combination of sucralose and acesulfame K is biologically active. While not affecting whole-body insulin resistance, it increases insulin sensitivity and glucose uptake in specific tissues, mimicking the effects of obesity in the adipose tissue and in the brain.

Chronic abdominal vagus stimulation increased brain metabolic connectivity, reduced striatal dopamine transporter and increased mid-brain serotonin transporter in obese miniature pigs

Background/objective

Changes in brain metabolism has been investigated thoroughly during unilateral cervical chronic vagal stimulation in epileptic or depressive patients. Bilateral stimulation of the abdominal vagus (_aVNS) has received less attention despite the reduction in body weight and an altered feeding behavior in obese animals that could be clinically relevant in obese individuals. Our study aims to examine the changes in brain glucose metabolism (CMR_glu) induced by _aVNS in obese adult miniature pigs. Dopamine (DAT) and serotonin transporters (SERT) were also quantified to further understand the molecular origins of the alterations in brain metabolism.

Subjects/methods

Pairs of stimulating electrodes were implanted during laparoscopy on both abdominal vagal trunks in 20 obese adult’s miniature pigs. Half of the animals were permanently stimulated while the remaining were sham stimulated. Two months after the onset of stimulation, dynamic ₁₈FDG PET and ¹²³I-ioflupane SPECT were performed. Food intake, resting energy expenditure and fat deposition were also assessed longitudinally.

Results

Food intake was halved and resting energy expenditure was increased by 60% in _aVNS group compared to sham. The gain in body weight was also 38% less in _aVNS group compared to sham. Brain metabolic connectivity increased between numerous structures including striatum, mid-brain, amygdala and hippocampus. On the contrary, increased CMR_glu were restricted to the thalamus, the periaqueducal grey and the amygdala. DAT binding potential was decreased by about one third in the striatum while SERT was about doubled in the midbrain.

Conclusions

Our findings demonstrated that _aVNS reduced weight gain as a consequence of diminished daily food intake and increased resting energy expenditure. These changes were associated with enhanced connectivity between several brain areas. A lower striatal DAT together with a doubled mid-brain SERT were likely causative for these changes.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1831-5) contains supplementary material, which is available to authorized users.

Comparison of the efficiency of chopped and non-rectangular electrical stimulus waveforms in activating small vagus nerve fibers

BACKGROUND

In the context of morbid obesity, vagus nerve stimulation could be used to control gastric function targeting the small afferent B-fibers and C-fibers. Compared to large A-fibers, activation thresholds of these small efferent fibers are 10 to 100 times greater, inducing technical constraints and possible nerve damages. Although rectangular waveform is commonly used in nerve stimulation, recent modeling and experimental studies suggest that non-rectangular waveforms could reduced the charge injected by the stimulator.

NEW METHOD

The objective of the present study is to evaluate the charge injection of complex waveforms such as the ramp, quarter sine and chopped pulses in the context of vagus nerve stimulation. We performed in-vivo study on the porcine abdominal vagus nerves and evaluated charge injection at activation thresholds. A modeling study was performed to further extent the results obtained in-vivo.

COMPARISON WITH EXISTING METHOD

Compared to the rectangular pulse, the ramp and quarter sine waveforms activated gastric fibers with the lowest charge injection: -23.2% and -30.1% respectively. The efficacy of chopped pulses is questioned through the consideration of the strength-duration curve.

CONCLUSION

Continuous ramp and quarter sine waveforms effectively activate small diameter fibers. These pulse shapes may be considered for long-term vagus nerve stimulation. The results predicted by computational models were qualitatively consistent with experiments. This suggested the relevance of using modeling in the context of complex waveforms prior to future in-vivo tests.

Gastric Emptying and Dynamic In Vitro Digestion of Drinkable Yogurts: Effect of Viscosity and Composition

Gastric emptying of food is mainly driven by the caloric concentration, the rheological properties of the chyme, and the physical state (liquid/solid) of food once in the stomach. The present work investigated: (1) The effect of the composition and the viscosity of drinkable yogurts on gastric emptying in pigs, and (2) the behavior of yogurts during dynamic in vitro digestion. Three isocaloric liquid yogurts were manufactured: Two enriched in protein and fiber showing either a low (LV) or high (HV) viscosity, one control enriched in sugar and starch (CT). They were labelled with 99mTc-sulfur colloid and given to pigs (n = 11) to determine gastric emptying pattern by gamma scintigraphy. Then dynamic in vitro digestion of the yogurts was done using the parameters of gastric emptying determined in vivo. Gastric emptying half-times were significantly longer for LV than CT, whereas HV exhibited an intermediate behavior. In vitro gastric digestion showed a quick hydrolysis of caseins, whereas whey proteins were more resistant in the stomach particularly for LV and HV. During the intestinal phase, both whey proteins and caseins were almost fully hydrolyzed. Viscosity was shown to affect the behavior of yogurt in the small intestine.

Impact of gastric emptying and small intestinal transit on blood glucose, intestinal hormones, glucose absorption in the morbidly obese

This study evaluated gastric emptying (GE) and small intestinal (SI) transit in people with morbid obesity and their relationships to glycaemia, incretin hormones, and glucose absorption METHODS: GE and caecal arrival time (CAT) of a mixed meal were assessed in 22 morbidly obese (50.2 ± 2.5 years; 13 F:9 M; BMI: 48.6 ± 1.8 kg/m²) and 10 lean (38.6 ± 8.4 years; 5 F:5 M; BMI: 23.9 ± 0.7 kg/m²) subjects, using scintigraphy. Blood glucose, plasma 3-O-methylglucose, insulin, glucagon, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) were measured. Insulin sensitivity and resistance were also quantified RESULTS: When compared with lean subjects, GE (t50: 60.7 ± 6.5 vs. 41.1 ± 7.3 min; P  = 0.04) and CAT (221.5 ± 9.8 vs. 148.0 ± 7.1 min; P =  0.001) of solids were prolonged in morbid obesity. Postprandial rises in GIP (P = 0.001), insulin (P  = 0.02), glucose (P = 0.03) and 3-O-methylglucose (P = 0.001) were less. Whereas GLP-1 increased at 45 mins post-prandially in lean subjects, there was no increase in the obese (P  = 0.04). Both fasting (P = 0.045) and postprandial (P = 0.012) plasma glucagon concentrations were higher in the obese CONCLUSIONS: GE and SI transit are slower in the morbidly obese, and associated with reductions in postprandial glucose absorption, and glycaemic excursions, as well as plasma GIP and GLP-1.

Inward Glucose Transfer Accounts for Insulin-Dependent Increase in Brain Glucose Metabolism Associated with Diet-Induced Obesity

OBJECTIVE

There is a general agreement that there are changes in brain metabolism in insulin-resistant individuals during conditions of hyperinsulinemia. However, the impact on obesity is unclear, and the metabolic constants underlying these modifications are unknown. The aim of this study was to evaluate these changes in a large animal model of diet-induced obesity.

METHODS

Twenty adult miniature pigs were fed with either an obesogenic diet or a regular diet for 5 months. At that time, fat deposition was evaluated using computed tomography scanning, and ¹⁸ fluorodeoxyglucose positron emission tomography images were acquired dynamically both in the fasted state and during a euglycemic-hyperinsulinemic clamp. Glucose uptake rates and pixel-wise modeled brain volumes were calculated together with brain connectivity.

RESULTS

Whole-body insulin sensitivity was reduced by more than 50% in the obesity group. During insulin stimulation, whole-brain insulin-induced increased glucose uptake was unaltered in lean animals but increased markedly in the animals with obesity. The increased glucose uptake reflected an increase in the inward transfer without changes in phosphorylation or outward brain transport. Connectivity was increased in the animals with obesity CONCLUSIONS: Diet-induced obesity is associated with an increase in insulin-stimulated brain glucose uptake as a consequence of a larger inward transfer. These changes occurred together with an increased connectivity in reference to regions associated with memory recollection.

Maternal Western diet during gestation and lactation modifies adult offspring's cognitive and hedonic brain processes, behavior, and metabolism in Yucatan minipigs

This study explores the long-term effects of exposure to a maternal Western diet (WD) vs. standard diet (SD) in the Yucatan minipig, on the adult progeny at lean status ( n = 32), and then overweight status. We investigated eating behavior, cognitive abilities, brain basal glucose metabolism, dopamine transporter availability, microbiota activity, blood lipids, and glucose tolerance. Although both groups demonstrated similar cognitive abilities in a holeboard test, WD pigs expressed a higher stress level than did SD pigs (immobility, P < 0.05) and lower performance in an alley maze ( P = 0.06). WD pigs demonstrated lower dopamine transporter binding potential in the hippocampus and parahippocampal cortex ( P < 0.05 for both), as well as a trend in putamen ( P = 0.07), associated with lower basal brain activity in the prefrontal cortex and nucleus accumbens ( P < 0.05) compared with lean SD pigs. Lean WD pigs demonstrated a lower glucose tolerance than did SD animals (higher glucose peak, P < 0.05) and a tendency to a higher incremental area under the curve of insulin from 0 to 30 minutes after intravenous glucose injection ( P < 0.1). Both groups developed glucose intolerance with overweight, but WD animals were less impacted than SD animals. These results demonstrate that maternal diet shaped the offspring's brain functions and cognitive responses long term, even after being fed a balanced diet from weaning, but behavioral effects were only revealed in WD pigs under anxiogenic situation; however, WD animals seemed to cope better with the obesogenic diet from a metabolic standpoint.-Gautier, Y., Luneau, I., Coquery, N., Meurice, P., Malbert, C.-H., Guerin, S., Kemp, B., Bolhuis, J. E., Clouard, C., Le Huërou-Luron, I., Blat, S., Val-Laillet, D. Maternal Western diet during gestation and lactation modifies adult offspring's cognitive and hedonic brain processes, behavior, and metabolism in Yucatan minipigs.

Obesity-Associated Alterations in Glucose Metabolism Are Reversed by Chronic Bilateral Stimulation of the Abdominal Vagus Nerve

Acute vagal stimulation modifies glucose and insulin metabolism, but the effect of chronic bilateral vagal stimulation is not known. Our aim was to quantify the changes in whole-body and organ-specific insulin sensitivities 12 weeks after permanent, bilateral, vagal stimulation performed at the abdominal level in adult mini-pigs. In 15 adult mini-pigs, stimulating electrodes were placed around the dorsal and ventral vagi using laparoscopy and connected to a dual-channel stimulator placed subcutaneously. Animals were divided into three groups based on stimulation and body weight (i.e., lean nonstimulated, obese nonstimulated, and obese stimulated). Twelve weeks after surgery, glucose uptake and insulin sensitivity were measured using positron emission tomography during an isoglycemic clamp. Mean whole-body insulin sensitivity was lower by 34% (P < 0.01) and the hepatic glucose uptake rate was lower by 33% (P < 0.01) in obese-nonstimulated mini-pigs but was no different in obese-stimulated compared with lean mini-pigs. An improvement in skeletal glucose uptake rate was also observed in obese-stimulated compared with obese-nonstimulated groups (P < 0.01). Vagal stimulation was associated with increased glucose metabolism in the cingulate and prefrontal brain areas. We conclude that chronic vagal stimulation improves insulin sensitivity substantially in diet-induced obesity by both peripheral and central mechanisms.

Effects of Chronic Consumption of Sugar-Enriched Diets on Brain Metabolism and Insulin Sensitivity in Adult Yucatan Minipigs

Excessive sugar intake might increase the risk to develop eating disorders via an altered reward circuitry, but it remains unknown whether different sugar sources induce different neural effects and whether these effects are dependent from body weight. Therefore, we compared the effects of three high-fat and isocaloric diets varying only in their carbohydrate sources on brain activity of reward-related regions, and assessed whether brain activity is dependent on insulin sensitivity. Twenty-four minipigs underwent ¹⁸FDG PET brain imaging following 7-month intake of high-fat diets of which 20% in dry matter weight (36.3% of metabolisable energy) was provided by starch, glucose or fructose (n = 8 per diet). Animals were then subjected to a euglycemic hyperinsulinemic clamp to determine peripheral insulin sensitivity. After a 7-month diet treatment, all groups had substantial increases in body weight (from 36.02±0.85 to 63.33±0.81 kg; P<0.0001), regardless of the diet. All groups presented similar insulin sensitivity index (ISI = 1.39±0.10 mL·min^-1·μUI·kg). Compared to starch, chronic exposure to fructose and glucose induced bilateral brain activations, i.e. increased basal cerebral glucose metabolism, in several reward-related brain regions including the anterior and dorsolateral prefrontal cortex, the orbitofrontal cortex, the anterior cingulate cortex, the caudate and putamen. The lack of differences in insulin sensitivity index and body weight suggests that the observed differences in basal brain glucose metabolism are not related to differences in peripheral insulin sensitivity and weight gain. The differences in basal brain metabolism in reward-related brain areas suggest the onset of cerebral functional alterations induced by chronic consumption of dietary sugars. Further studies should explore the underlying mechanisms, such as the availability of intestinal and brain sugar transporter, or the appearance of addictive-like behavioral correlates of these brain functional characteristics.

Obesogenic diets have deleterious effects on fat deposits irrespective of the nature of dietary carbohydrates in a Yucatan minipig model

The effects of digestible carbohydrates, fructose in particular, on the development of metabolic disturbances remain controversial. We explored the effects of prolonged consumption of high-fat diets differing in their carbohydrate source on fat deposits in the adult Yucatan minipig. Eighteen minipigs underwent computed tomographic imaging and blood sampling before and after 8 weeks of three isocaloric high-fat diets with different carbohydrate sources (20% by weight for starch in the control diet, glucose or fructose, n=6 per diet). Body adiposity, liver volume, and fat content were estimated from computed tomographic images (n=18). Liver volume and lipid content were also measured post mortem (n=12). We hypothesized that the quantity and the spatial distribution of fat deposits in the adipose tissue or in the liver would be altered by the nature of the carbohydrate present in the obesogenic diet. After 8 weeks of dietary exposure, body weight (from 26±4 to 58±3 kg), total body adiposity (from 38±1 to 47±1%; P<.0001), liver volume (from 1156±31 to 1486±66 mL; P<.0001), plasma insulin (from 10±1 to 14±2 mIU/L; P=.001), triacylglycerol (from 318±37 to 466±33 mg/L; P=.005), and free-fatty acids (from 196±60 to 396±59 μmol/L; P=.0001) increased irrespective of the carbohydrate type. Similarly, the carbohydrate type did not induce changes in the spatial repartition of the adipose tissue. Divergent results were obtained for fat deposits in the liver depending on the investigation method. In conclusion, obesogenic diets alter adipose tissue fat deposits and the metabolic profile independently of the nature of dietary carbohydrates.

Vagus nerve stimulation: state of the art of stimulation and recording strategies to address autonomic function neuromodulation

OBJECTIVE

Neural signals along the vagus nerve (VN) drive many somatic and autonomic functions. The clinical interest of VN stimulation (VNS) is thus potentially huge and has already been demonstrated in epilepsy. However, side effects are often elicited, in addition to the targeted neuromodulation.

APPROACH

This review examines the state of the art of VNS applied to two emerging modulations of autonomic function: heart failure and obesity, especially morbid obesity.

MAIN RESULTS

We report that VNS may benefit from improved stimulation delivery using very advanced technologies. However, most of the results from fundamental animal studies still need to be demonstrated in humans.

Dietary α-lactalbumin supplementation alleviates normocaloric western diet-induced glucose intolerance in Göttingen minipigs

OBJECTIVE

The pandemic of obesity in Western countries is mainly due to the high-fat, high-energy diet prevailing there. Obesity-associated metabolic disorders are the consequence of fat mass increase leading to altered adipokine secretion, hyperlipemia, oxidant stress, low-grade inflammation, and eventually glucose intolerance. Yet not all people consuming a Western diet become obese, and the question is raised whether these people are also at risk of developing metabolic disorders.

METHODS

Glucose tolerance, lipid profile, and oxidant and inflammation status were investigated longitudinally in lean Göttingen minipigs receiving for 16 weeks either a normal diet (ND), a Western diet (WD), or a Western diet supplemented with a whey protein isolate (WPI) rich in α-lactalbumin known to improve glucose tolerance. ND and WD were supplied isoenergetically.

RESULTS

Lean minipigs fed WD displayed glucose intolerance and altered lipid profile after 6 weeks of diet but no inflammation or oxidative stress. Supplementation with WPI alleviated glucose intolerance by improving insulin secretion, but not lipid profile.

CONCLUSIONS

Western diet consumption is deleterious for glucose tolerance even in the absence of fat mass accretion, and dyslipemia is a major determinant for this metabolic dysfunction. Stimulating insulin secretion with a WPI is an effective strategy to improve glucose tolerance.

Combined compared to dissociated oral and intestinal sucrose stimuli induce different brain hedonic processes

The characterization of brain networks contributing to the processing of oral and/or intestinal sugar signals in a relevant animal model might help to understand the neural mechanisms related to the control of food intake in humans and suggest potential causes for impaired eating behaviors. This study aimed at comparing the brain responses triggered by oral and/or intestinal sucrose sensing in pigs. Seven animals underwent brain single photon emission computed tomography (^99mTc-HMPAO) further to oral stimulation with neutral or sucrose artificial saliva paired with saline or sucrose infusion in the duodenum, the proximal part of the intestine. Oral and/or duodenal sucrose sensing induced differential cerebral blood flow changes in brain regions known to be involved in memory, reward processes and hedonic (i.e., pleasure) evaluation of sensory stimuli, including the dorsal striatum, prefrontal cortex, cingulate cortex, insular cortex, hippocampus, and parahippocampal cortex. Sucrose duodenal infusion only and combined sucrose stimulation induced similar activity patterns in the putamen, ventral anterior cingulate cortex and hippocampus. Some brain deactivations in the prefrontal and insular cortices were only detected in the presence of oral sucrose stimulation. Finally, activation of the right insular cortex was only induced by combined oral and duodenal sucrose stimulation, while specific activity patterns were detected in the hippocampus and parahippocampal cortex with oral sucrose dissociated from caloric load. This study sheds new light on the brain hedonic responses to sugar and has potential implications to unravel the neuropsychological mechanisms underlying food pleasure and motivation.

[The brain-gut axis: insights from the obese pig model]

The pig, which shares several similarities with humans, is increasingly used for biomedical research, particularly in nutrition and neurosciences. Recent studies in minipigs have shown that a deleterious nutritional environment (e.g. a high-fat and high-sugar diet) induces obesity which, as in humans, is associated with increased adiposity, insulin resistance, modified eating behaviour, and altered gastric function and intestinal sensitivity. These changes are accompanied by differences in the activation matrices and metabolic activity of several brain areas. Using this animal model, we have revisited the concept of dual hedonic and homeostatic control of food intake. We have thus developed a minimally invasive and potentially reversible surgical approach to the control of food intake, as an alternative to bariatric surgery, based on chronic vagal stimulation at the abdominal level.

Exposures to conditioned flavours with different hedonic values induce contrasted behavioural and brain responses in pigs

This study investigated the behavioural and brain responses towards conditioned flavours with different hedonic values in juvenile pigs. Twelve 30-kg pigs were given four three-day conditioning sessions: they received three different flavoured meals paired with intraduodenal (i.d.) infusions of 15% glucose (F(Glu)), lithium chloride (F(LiCl)), or saline (control treatment, F(NaCl)). One and five weeks later, the animals were subjected to three two-choice feeding tests without reinforcement to check the acquisition of a conditioned flavour preference or aversion. In between, the anaesthetised pigs were subjected to three (18)FDG PET brain imaging coupled with an olfactogustatory stimulation with the conditioned flavours. During conditioning, the pigs spent more time lying inactive, and investigated their environment less after the F(LiCl) than the F(NaCl) or F(Glu) meals. During the two-choice tests performed one and five weeks later, the F(NaCl) and F(Glu) foods were significantly preferred over the F(LICl) food even in the absence of i.d. infusions. Surprisingly, the F(NaCl) food was also preferred over the F(Glu) food during the first test only, suggesting that, while LiCl i.d. infusions led to a strong flavour aversion, glucose infusions failed to induce flavour preference. As for brain imaging results, exposure to aversive or less preferred flavours triggered global deactivation of the prefrontal cortex, specific activation of the posterior cingulate cortex, as well as asymmetric brain responses in the basal nuclei and the temporal gyrus. In conclusion, postingestive visceral stimuli can modulate the flavour/food hedonism and further feeding choices. Exposure to flavours with different hedonic values induced metabolism differences in neural circuits known to be involved in humans in the characterization of food palatability, feeding motivation, reward expectation, and more generally in the regulation of food intake.

Changes in brain activity after a diet-induced obesity

Compared to lean subjects, obese men have less activation in the dorsolateral prefrontal cortex, a brain area implicated in the inhibition of inappropriate behavior, satiety, and meal termination. Whether this deficit precedes weight gain or is an acquired feature of obesity remains unknown. An adult animal model of obesity may provide insight to this question since brain imaging can be performed in lean vs. obese conditions in a controlled study. Seven diet-induced obese adult minipigs were compared to nine lean adult minipigs housed in the same conditions. Brain activation after an overnight fasting was mapped in lean and obese subjects by single photon emission computed tomography. Cerebral blood flow, a marker of brain activity, was measured in isoflurane-anesthetized animals after the intravenous injection of 99mTc-HMPAO (750 MBq). Statistical analysis was performed using statistical parametric mapping (SPM) software and cerebral blood flow differences were determined using co-registered T1 magnetic resonance imaging (MRI) and histological atlases. Deactivations were observed in the dorsolateral and anterior prefrontal cortices in obese compared to lean subjects. They were also observed in several other structures, including the ventral tegmental area, the nucleus accumbens, and nucleus pontis. On the contrary, activations were found in four different regions, including the ventral posterior nucleus of the thalamus and middle temporal gyrus. Moreover, the anterior and dorsolateral prefrontal cortices as well as the insular cortex activity was negatively associated with the body weight. We suggested that the reduced activation of prefrontal cortex observed in obese humans is probably an acquired feature of obesity since it is also found in minipigs with a diet-induced obesity.

A three-dimensional digital segmented and deformable brain atlas of the domestic pig

We used high-magnetic field (4.7 T) magnetic resonance imaging (MRI) to build the first high-resolution (100 microm x 150 microm x 100 microm) three-dimensional (3D) digital atlas in stereotaxic coordinates of the brain of a female domestic pig (Sus scrofa domesticus). This atlas was constructed from one hemisphere which underwent a symmetrical transformation through the midsagittal plane. Concomitant construction of a 3D histological atlas based on the same scheme facilitated control of deep brain structure delimitation and enabled cortical mapping to be achieved. The atlas contains 178 individual cerebral structures including 42 paired and 9 single deep brain structures, 5 ventricular system areas, 6 paired deep cerebellar nuclei, 12 cerebellar lobules and 28 cortical areas per hemisphere. Given the increasing importance of pig brains in medical research, this atlas should be a useful tool for intersubject normalization in anatomical imaging as well as for precisely localizing brain areas in functional MR studies or electrode implantation trials. The atlas can be freely downloaded from our institution's Website.

Subthalamic nucleus stimulation in Parkinson disease induces apathy: a PET study

OBJECTIVE

Apathy may be induced by subthalamic nucleus deep brain stimulation (STN-DBS) in Parkinson disease (PD). We therefore wished to test the hypothesis that apathy induced by STN-DBS correlates with changes in glucose metabolism, using (18)FDG-PET.

METHODS

Twelve patients with PD were assessed 3 months before (M-3) and 3 months after (M+3) STN-DBS with (18)FDG-PET and the Apathy Evaluation Scale.

RESULTS

Apathy had significantly worsened at M+3 after STN-DBS. Positive correlations were observed between this variation in apathy scores and changes in glucose metabolism, especially in the right frontal middle gyrus (Brodmann area [BA] 10) and right inferior frontal gyrus (BA 46 and BA 47). Negative correlations between the two were observed in the right posterior cingulate gyrus (BA 31) and left medial frontal lobe (BA 9).

CONCLUSION

These preliminary results confirm the role of the subthalamic nucleus in associative and limbic circuitry in humans and suggest that it is a key basal ganglia structure in motivation circuitry.

Influence of the selective neuronal NO synthase inhibitor ARL 17477 on nitrergic neurotransmission in porcine stomach

Selective neuronal NOS (nNOS) inhibitors have been developed for possible application in cerebral ischemia and neurodegenerative disorders. To investigate the degree of interference with peripheral nNOS, the influence of the selective nNOS inhibitor ARL 17477 was studied on electrically induced nitrergic relaxations in pig gastric fundus strips and on gastric fundic compliance in conscious pig. Circular muscle strips of porcine gastric fundus were electrically stimulated (10 s trains at 4 Hz, 0.1 ms and 40 V). ARL 17477 inhibited the electrically induced relaxations in a concentration-dependent way (3x10(-6) M-10(-4) M). The inhibitory effect of ARL 17477 developed more progressively than that of N(G)-nitro-L-arginine methyl ester (L-NAME; 3x10(-4) M). In conscious pigs, instrumented with a fundic cannula, L-NAME (20 mg/kg i.v.) significantly increased mean arterial blood pressure and decreased fundic compliance in the fasted state (71+/-13 ml/mm Hg versus 185+/-37 ml/mm Hg after saline; P<0.05). ARL 17477 (3 mg/kg, i.v.) did not influence blood pressure but influenced gastric fundic volume-pressure curves in a similar way as L-NAME. Plasma concentration analysis of ARL 17477 indicated a half-life of less than 30 min in pig. ARL 17477 thus inhibits the effect of nitrergic neurons in the pig gastric fundus in vitro, leading to inhibited gastric compliance in the conscious pig. The study indicates that selective nNOS inhibitors, applied for cerebral disorders, might also interfere with neuronal nitrergic regulation of gastrointestinal motility.

Insulin modulates duodenal vagal afferents basal activity

Hyperglycemia markedly modifies gastro-duodenal motility. The question was raised whether hyperinsulinaemia, which is usually concomitant to hyperglycemia, could be the factor responsible for this effect through alteration of gastro-duodenal sensitivity. Indeed, vagal receptors are directly activated by insulin in lambs. However, insulin action significantly differs in ruminants and non-ruminants. The aim of our study was therefore to check (i) if insulin per se was able to modulate basal and distension induced discharges of duodenal vagal afferents in a monogatric animal model and (ii) if its action was direct or indirect through changes in gut compliance. Fourteen duodenal mechanoreceptors were studied in anaesthetized curarized pigs using the "single-fiber" method performed on the left cervical vagus. The characteristics of the vagal receptors were studied before (Control), and after (i) local insulin infusion in the gastroepiploic artery (IA), (ii) IV insulin perfusion inducing systemic hypoglycemia (IV), and (iii) during an euglycemic hyperinsulinemic clamp (EH). Basal recording, isobaric and isovolumetric distensions were performed in all experimental conditions. Basal discharge was significantly increased during IA (5.8+/-0.28 spikes/5 s), IV (6.6+/-0.30 spikes/5 s) and EH (5.7+/-0.25 spikes/5 s) compared to Control (4.4+/-0.27 spikes/5 s, p<0.05). Responses during isobaric and isovolumetric distensions were identical irrespective of the experimental condition. Gut compliance and intraluminal pressure during basal recording were not modified (p>0.05). In conclusion, insulin increased duodenal vagal mechanoreceptors basal activity but did not modulate the mechanosensitivity of the vagal units. Insulin-induced increase in basal discharge rate was due to hyperinsulinemia per se since it persisted during the euglycemic hyperinsulinemic clamp.

Involvement of NO in gastric emptying of semi-solid meal in conscious pigs

The influence of non-selective nitric oxide synthase (NOS) inhibition on gastric emptying of a semi-solid meal was studied in conscious pigs. Antroduodenal motility and fundic compliance were also assessed to evaluate the mechanisms at the origin of potential alteration in gastric emptying pattern. N(G)-nitro-L-arginine methyl ester (L-NAME; 20 mg kg(-1) i.v.) delayed gastric emptying (half-emptying time of 128.98 +/- 16.86 min vs 73.74 +/- 7.73 min after saline, P < 0.05, n = 6) as a result of decreased proximal gastric emptying. No changes were observed for distal gastric emptying as a result of unchanged antral motility. Similarly, no changes were noted on duodenal motor patterns either in the fasted or in the fed state. L-NAME decreased fundic compliance in fasted state (49 +/- 11 mL mmHg(-1) vs 118 +/- 15 mL mmHg(-1) after saline, P < 0.05, n = 6). As this phenomenon is expected to increase emptying rate, the gastroparesis induced by NOS inhibition is thus likely to originate from distal resistive forces. It is concluded that NO positively modulates gastric emptying.

Development of 99mTc labelled Lipiodol: biodistribution following injection into the hepatic artery of the healthy pig

BACKGROUND

We develop a method for the radiolabelling of Lipiodol with Tc, using a lipophilic complex, [99mTc-(S2CPh)(S3Ph)2], dissolved in Lipiodol (99mTc-SSS Lipiodol).

RESULTS

The labelling yield is high (96 +/- 0.8%), and the radiochemical purity satisfactory (92 +/- 2.6%). This labelling is reproducible and stable for up to 24 h in vitro. Studies carried out after injection into the hepatic artery of the healthy pig show that the biodistribution of 99mTc-SSS Lipiodol is comparable with that observed for 188Re Lipiodol.

MATERIALS AND METHODS

The 99mTc-SSS lipiodol was obtained after dissolving a chelating agent, previously labelled with 99mTc, in cold lipiodol. The radiochemical purity (RCP) of the labelling was checked immediately and at 24 h. The 99mTc-SSS lipiodol was injected into the hepatic artery of four healthy pigs for an ex-vivo biodistribution study. An autoradiographic study was performed in two cases.

CONCLUSIONS

Apart from the specific interest of a Lipiodol-bearing technetiated agent for carrying out dosimetric studies, the labelling of Lipiodol with 99mTc is a preliminary step towards the use of radiolabelling with the 188Re analogue.

The vagus is inhibitory of the late postprandial insulin secretion in conscious pigs

The vagus is involved in the cephalic phase of insulin secretion but its role in the meal absorption phase of insulin release remains to be defined. The aim of this study was therefore to evaluate the role of the vagus in the early and the late meal absorption phases of insulin secretion. In six pigs, venous insulin profiles were compared in intact animals, after ventral or dorsal vagal trunk section, and after section of both vagal trunks (truncal vagotomy). Since gastric emptying could be modified by vagotomy, it was recorded concomitantly by gamma scintigraphy. Semi-solid (porridge) and liquid (glucose 10%) meals were tested. Truncal vagotomy significantly increased insulin release compare to intact animals after glucose (63.8%) and porridge (174.4%) meals in the early and the late absorption phases of insulin secretion, respectively. For the glucose meal, this effect could be explained by a vagally mediated change in gastric emptying rate, since insulin concentrations for a similar amount of nutrient propelled to the duodenum were not different in intact and truncal vagotomized animals. In contrast, after the porridge meal, truncal vagotomy was associated with a second, later occurring increase in circulating insulin, which could not be explained by changes in gastric emptying rate. These results demonstrate for the first time an inhibitory role of the vagus in the late meal absorption phase of insulin release.

Human duodenal phase III migrating motor complex activity is predominantly antegrade, as revealed by high-resolution manometry and colour pressure plots

Abstract Late phase III migrating motor complex activity has been said to be primarily retroperistaltic but has not been assessed with high resolution manometry or three-dimensional colour pressure plots (pressure/time/distance). Duodenal phase III was examined in healthy young volunteers (seven male, two female) with a 20-lumen assembly. With the most proximal sidehole in the distal antrum, after a 4.5-cm interval 18 sideholes at 1.5-cm intervals spanned the duodenum with a final sidehole 3 cm beyond. Fasting pressures were recorded until phase III occurred. Comparisons were made between proximal (P) and distal (D) duodenum during early (E) (first 0.5-1 min) and late (L) (last 0.5-1 min) phase III. With colour pressure analysis, 121 of 180 pressure wave (PW) sequences were purely antegrade, two purely retrograde and 57 bidirectional. Ten of fifty-seven bidirectional PW sequences were complex, branching to become two separate sequences. Bidirectional sequences occurred more frequently in late than early phase III (L 43 vs. E 14 of 57), but their occurrence did not differ between proximal and distal duodenum (P31 vs. D 24 of 57). Antegrade propagation velocity was faster in late compared with early phase III (L 28.50 vs. E 17.05 mm s(-1); P = 0.006), but did not differ between proximal and distal duodenum. Colour pressure analysis also indicated an intermittent segmental pattern to phase III, with each subject exhibiting a change in velocity or direction, or a relative failure of peristalsis somewhere along the duodenum during part of phase III. Duodenal phase III is not homogenous and, in contrast with previous studies, does not primarily constitute a retroperistaltic pump. Colour pressure analysis is useful in interpreting intraluminal pressure profiles and may improve the sensitivity and specificity of clinical studies.

Antropyloroduodenal, cholecystokinin and feeding responses to pulsatile and non-pulsatile intraduodenal lipid infusion

The contribution of the pulsatile nature of gastric emptying to small intestinal feedback mechanisms modulating antropyloroduodenal motility and appetite is unknown. On separate days, eight healthy male volunteers (18-34 years) received randomized, single-blind, intraduodenal (ID) infusions of 10% Intralipid (2 kcal min(-1)), either continuously [CID], or in a pulsatile manner [PID] (5 s on/15 s off) and 0.9% saline (control) administered continuously, each at a rate of 1.8 mL min(-1) for 3 h. During each infusion, subjective ratings of appetite were assessed and antropyloroduodenal pressures recorded with a 16-lumen manometric assembly incorporating a pyloric sleeve sensor. Plasma cholecystokinin was measured from blood collected at regular intervals throughout the infusion. At the end of each infusion the manometric assembly was removed, subjects were offered a buffet meal and the energy and macronutrient content of the meal was measured. Both ID lipid infusions stimulated isolated pyloric pressure waves (IPPWs) (P < 0.001) and basal pyloric pressure (P < 0.01) and suppressed antral (P < 0.05) and duodenal (P < 0.05) pressure waves when compared to controls; there was no difference in the effects of CID and PID lipid on antropyloroduodenal pressures. Infusions of lipid significantly increased plasma CCK concentrations (P < 0.05) compared with saline, but concentrations were not different between the two modes of lipid delivery (P > 0.05, CID vs. PID). Both intraduodenal lipid infusions decreased hunger (P < 0.05), increased fullness (P < 0.05) and reduced energy intake (P < 0.05) when compared with controls; again there was no difference between CID and PID lipid. We conclude that at the infusion rate of similar 2 kcal min(-1), the acute effects of intraduodenal lipid on antropyloroduodenal pressures, plasma CCK concentration and appetite are not modified by a pulsatile mode of lipid delivery into the duodenum.

The vagus is inhibitory of insulin secretion under fasting conditions

The involvement of the vagus in the insulin response during the early phase of absorption of a meal has been demonstrated recently. The extent of this vagal influence was investigated during fasting in an anesthetized porcine model. Portal and systemic insulin were evaluated together with glycemia during cooling and sectioning of both cervical vagal trunks in 12 splanchnicotomized or sham-operated pigs. In sham-operated animals, portal and systemic insulin were significantly and reversibly increased by cooling (173 and 123%, respectively). Portal insulin peaked 20 min after the onset of cooling but declined slowly while cooling was still activated. In contrast, systemic insulin was increased evenly along cooling. Section of the vagus was also associated with a portal and systemic insulin increase (144 and 117%) but to a lesser extent than cooling. In both treatments, portal and systemic insulin increases were either reduced (vagal cooling) or eliminated (vagal section) in splanchnicotomized animals. We conclude that the vagus exerts an inhibitory activity on interdigestive insulin secretion that is partly mediated by the splanchnic nerves.

Desensitization of ileal vagal receptors by short-chain fatty acids in pigs

Coloileal reflux episodes trigger specialized ileal motor activities and inhibit gastric motility in pigs. The initiation of these events requires the detection by the distal ileum of the invading colonic contents that differ from the ileal chyme primarily in short-chain fatty acid (SCFA) concentrations. In addition to the already described humoral pathway, this detection might also involve ileal vagal afferents. Sensitivity to SCFA of 12 ileal vagal units was investigated in anesthetized pigs with single-unit recording at the left cervical vagus. SCFA mixtures (0.35, 0.7, and 1.4 mol/l) containing acetic, propionic, and butyric acids in proportions identical to that in the porcine cecocolon were compared with isotonic and hypertonic saline. All units behaved as slowly adapting mechanoreceptors (half-adaptation time = 35.4 +/- 15.89 s), and their sensitivity to local mechanical probing was suppressed by local anesthesia; 7 units significantly decreased their spontaneous firing with 0.7 and 1.4 but not 0.35 mol/l SCFA infusion compared with hypertonic or isotonic saline. Similarly, the response induced by distension in the same seven units was reduced (5 neurons) or abolished (2 neurons) after infusion of 0.7 (22.8 +/- 2.39 impulses/s) and 1.4 (30.3 +/- 2.12 impulses/s) mol/l SCFA solutions compared with isotonic saline (38.6 +/- 4.09 impulses/s). These differences in discharge were not the result of changes in ileal compliance, which remained constant after SCFA. In conclusion, SCFA, at concentrations near those found during coloileal reflux episodes, reduced or abolished mechanical sensitivity of ileal vagal afferents.

Changes in intragastric meal distribution are better predictors of gastric emptying rate in conscious pigs than are meal viscosity or dietary fibre concentration

The effect of dietary fibre on the gastric emptying rate of solids is controversial. Similarly, the mechanisms by which it modulates food intake are partially unknown. Gastric emptying and proximal v. distal stomach filling were evaluated in triplicate on four conscious pigs using scintigraphic imaging. Each animal received in an isoenergetic manner a concentrate low-fibre diet enriched in starch (S) and two high-fibre diets based on sugar beet pulp (BP) or wheat bran (WB). All meals had the same viscosity before ingestion (100.0-100.5 Pa.s). Viscosity of the gastric contents was measured in four additional animals fitted with a gastric cannula. The gastric emptying rate of BP diet was significantly slower than S and WB diets (t1/2 78.4 (sem 5.68), 62.8 (sem 10.01) and 111.6 (sem 10.82) min for S, WB and BP diets respectively, P<0.05). For BP diet only, rate of distal stomach filling was steady during the first 120 min after the meal whereas that of S and WB diets decreased in an exponential manner. Numerous backflow episodes from the distal into the proximal stomach were observed for BP diet that generated the larger intragastric viscosity (0.26 (sem 0.03), 0.3 (sem 0.02) and 0.52 (sem 0.002) Pa.s for S, WB and BP respectively). In conclusion, viscosity of the meal or the percentage total fibre, unlike viscosity of the gastric contents, are poor predictors for emptying. The reduced emptying rate observed with BP is associated with major changes in intragastric distribution of the meal absent with WB and S diets.

Nutrient-induced spatial patterning of human duodenal motor function

The spatiotemporal patterning of duodenal motor function has been evaluated comprehensively for the first time in humans, with a novel 21-lumen manometric assembly. In nine young, healthy volunteers (6 male, 3 female), duodenal motility was recorded during fasting and three 45-min intraduodenal (ID) nutrient infusion periods (Intralipid at 0.25, 0.5, and 1.5 kcal/min). Pressures were recorded along the length of the duodenum with an array of 18 sideholes at 1.5-cm intervals. Pressure patterns were compared for the final 20 min of each of the four periods. Compared with fasting, ID lipid was associated with regional variation in pressure wave (PW) sequences, with fewer proximally and more distally; this was not observed during fasting (P < 0.001). During fasting and all rates of lipid infusion, most (87-90%) PW sequences were short (1.5-4.5 cm), with a small number (2-4%) of 10.5 cm or longer. At all times, antegrade PW sequences occurred more frequently than retrograde sequences over all distances examined (3, 4.5, and >6 cm), and the proportion of antegrade sequences increased with greater PW sequence length (P = 0.0001). Increasing ID lipid rates appeared to produce dose-related suppression of PW sequences (P < 0.001). The frequency and spatial patterning of human duodenal motor function show substantial variability in response to different nutrient delivery rates. These complex patterns are likely to be involved in duodenal modulation of flow and gastric emptying rate.

Role of vagal innervation on intragastric distribution and emptying of liquid and semisolid meals in conscious pigs

The role of vagal innervation on emptying patterns and intragastric distributions of liquid and semisolid meals is still controversial. We aimed to record these features after dorsal, ventral and truncal vagotomies, using external gamma scintigraphy in conscious pigs in which the dorsal vagus specifically innervates the proximal stomach. Imaging of the stomach was performed for all experimental situations and before surgery using 99mTc-labelled glucose and porridge meals. Emptying of liquids was faster after dorsal vagotomy, whereas it was unchanged after ventral and truncal vagotomies (T1/2 = 57 +/- 8.5, 31 +/- 14.4, 54 +/- 9.1 and 42 +/- 14.9 min for intact, dorsal, ventral and truncal vagotomies, respectively). On the other hand, truncal vagotomy significantly reduced the emptying rate of semisolids whereas dorsal and ventral vagotomies had no significant effect (T1/2 = 96 +/- 7.2, 113 +/- 8.1, 75 +/- 9.9 and 260 +/- 56.6 min for intact, dorsal, ventral and truncal vagotomies). Morphological analysis of the gastric shape confirmed an overdistended proximal stomach after truncal vagotomy only. For semisolids, proximal stomach emptying followed the same emptying pattern as the entire stomach, irrespective of the surgical procedure. We concluded that the proximal stomach is the main control for the emptying of liquids and semisolids. The vagal control of overall gastric emptying for semisolids is probably identical to that modulating the intragastric distribution of the meal.

Ileal short-chain fatty acids inhibit gastric motility by a humoral pathway

The aim of this study was to evaluate the nervous and humoral pathways involved in short-chain fatty acid (SCFA)-induced ileal brake in conscious pigs. The role of extrinsic ileal innervation was evaluated after SCFA infusion in innervated and denervated Babkin's ileal loops, and gastric motility was measured with strain gauges. Peptide YY (PYY) and glucagon-like peptide-1 (GLP-1) concentrations were evaluated in both situations. The possible involvement of absorbed SCFA was tested by using intravenous infusion of acetate. Ileal SCFA infusion in the intact terminal ileum decreased the amplitude of distal and terminal antral contractions (33 +/- 1.2 vs. 49 +/- 1.2% of the maximal amplitude recorded before infusion) and increased their frequency (1.5 +/- 0.11 vs. 1.3 +/- 0.10/min). Similar effects were observed during SCFA infusion in ileal innervated and denervated loops (amplitude, 35 +/- 1.0 and 34 +/- 0. 8 vs. 47 +/- 1.3 and 43 +/- 1.2%; frequency, 1.4 +/- 0.07 and 1.6 +/- 0.06 vs. 1.1 +/- 0.14 and 1.0 +/- 0.12/min). Intravenous acetate did not modify the amplitude and frequency of antral contractions. PYY but not GLP-1 concentrations were increased during SCFA infusion in innervated and denervated loops. In conclusion, ileal SCFA inhibit distal gastric motility by a humoral pathway involving the release of an inhibiting factor, which is likely PYY.

The stimulation of antral motility by erythromycin is attenuated by hyperglycemia

OBJECTIVE

Diabetic gastroparesis is usually treated with prokinetic drugs, of which the most potent, when given intravenously during euglycemia, is erythromycin. Recent studies have demonstrated that the gastrokinetic effects of erythromycin are attenuated by hyperglycemia. The aim of this study was to determine whether the effects of erythromycin on antropyloroduodenal motility, including the organization of antral pressure waves, are modified by hyperglycemia.

METHODS

A total of eight healthy male volunteers (median age 24 yr) were studied on 2 days each in randomized order. A manometric assembly, incorporating six antral, two pyloric, and seven duodenal sideholes and a pyloric sleeve sensor, was positioned with the sleeve spanning the pylorus. The blood glucose concentration was stabilized at about 5 mmol/L (euglycemia) or 15 mmol/L (hyperglycemia). After 30 min (T = 0), an intraduodenal lipid infusion (1.5 kcal/min) was commenced and continued until the end of the study. At T = 20 minutes, erythromycin (200 mg) as the lactobionate was infused intravenously over 20 min, followed by 100 mg over the next 40 min.

RESULTS

Intravenous erythromycin increased the amplitude of antral waves during intraduodenal lipid infusion at both blood glucose concentrations (p < 0.01 for euglycemia and p < 0.05 for hyperglycemia). After erythromycin (T = 20 to T = 80), the frequency (p < 0.05) and amplitude (p < 0.01) of antral waves were less during hyperglycemia than euglycemia. Both propagated (p < 0.0005) and nonpropagated (p < 0.01) antral waves were decreased by hyperglycemia, but the suppression of propagated waves was greater (p < 0.05). Erythromycin reduced the frequency (p = 0.09) but increased the amplitude (p < 0.05) of phasic pyloric pressures, and decreased basal pyloric pressure (p < 0.0005). The frequency (p = 0.06) and amplitude (p < 0.05) of phasic pyloric waves during erythromycin infusion were slightly less during hyperglycemia than euglycemia, whereas there was no effect of the blood glucose concentration on basal pyloric pressure. Erythromycin increased the amplitude (p < 0.001) but not the frequency of duodenal waves; the frequency and amplitude of duodenal waves did not differ between the two blood glucose concentrations.

CONCLUSIONS

Hyperglycemia attenuates the stimulation of antral pressures and propagated antral sequences by erythromycin, but not the effects of erythromycin on pyloric or duodenal motility.

Metabolic acidosis and respiratory acidosis impair gastro-pyloric motility in anesthetized pigs

Acidosis impairs smooth muscle function in various organs. However, the effects of acidosis on the gastroduodenal tract are unknown while its dysfunction has potential perioperative harmful consequences. We investigated the effects of metabolic (MA) and respiratory acidosis (RA) on upper gut motility in tracheally ventilated pigs whose anesthesia was induced with halothane and maintained with alpha-chloralose-urethane administration (IV). Increased dead space and perfusion of hydrochloric acid 1 N (150 mL over 30 min) were used to induce RA and MA, respectively. Measurements of fundic tone using an electronic barostat, antro-pyloroduodenal phasic motility with perfused manometry and antro-duodenal electric control activity by electromyography were used to evaluate gastroduodenal function. Acidosis increased the fundic tone as reflected by a decrease in barostat volumes from 275+/-83 to 194+/-88 mL for MA and from 278+/-93 to 236+/-106 mL for RA. Pyloric and duodenal basal tones were not affected by either acidosis. A decrease in pyloric contraction amplitude from 95+/-24 to 62+/-26 mm Hg during MA and from 94+/-26 to 64+/-20 mm Hg during RA was observed. Both acidosis altered antral control activity that became dysrhythmic. Acidosis could be implicated in perioperative complications, such as gastroparesis, emesis, and regurgitation of gastric contents.

IMPLICATIONS

Metabolic and respiratory acidosis mainly affects gastric antral rhythms and has a major effect on fundic tone. Acidosis could be implicated in perioperative complications, such as gastroparesis, emesis, and regurgitation of gastric contents.

Short-chain fatty acids present in the ileum inhibit fasting gastrointestinal motility in conscious pigs

Colonic compounds, primarily short-chain fatty acids (SCFAs), inhibit gastric tone in humans. However, since colonic compounds reflux into the ileum, SCFAs might act also at the ileal level. This study evaluates the effects of the contact of SCFAs with the ileum alone towards gastrointestinal motility in fasted conscious pigs. Gastrointestinal motility was recorded during ileal infusion of a mixture containing acetate, propionate and butyrate in intact vs ileostomized animals (n = 10). Ileal infusions of isomolar (500 mmol L-1) vs isocaloric (600 kJ L-1) SCFAs were also performed. SCFA mixture reduced significantly the amplitude and increased the frequency of antral contractions in intact (motility index: 2624 +/- 503.4 vs 4077 +/- 388.2) and ileostomized pigs (motility index: 2428 +/- 678.1 vs 4709 +/- 773.4) compared with iso-osmotic saline. SCFAs at isomolar concentrations inhibited equally gastric motor pattern irrespective of their chemical structure. On the contrary, isocaloric concentrations of SCFAs induced graded effects: acetic acid being the most potent to reduce gastric motility. In conclusion, SCFAs inhibit gastrointestinal motility by a direct contact with the ileum. This inhibition was concentration dependent.