Intragastric balloon reduces food intake and body weight in rats

Impact of Vagotomy on Postoperative Weight Loss, Alimentary Intake, and Enterohormone Secretion After Bariatric Surgery in Experimental Translational Models

Obesity may be treated by bariatric procedures and is related to enterohormone release modulation. Nevertheless, a majority of commonly used surgical procedures have a significant impact on vagus nerve function by breaking the connections with its gastric branches. In the case of an intragastric balloon (BAL), this interaction is unclear. However, BAL-induced weight reduction is not long-lasting. Interestingly, this method has not been used in combination with vagotomy (VAG). Thus, we evaluated, for the first time, the short- and long-term effects of combined BAL and VAG using the animal-based translational model and compared these effects with sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB). Wistar rats were fed a high-calorie diet for 8 weeks to induce obesity before SG, RYGB, BAL + / - VAG. Animals' weight and eating behaviors were monitored weekly. After 90 days, serum samples were collected to evaluate postprandial and fasting GLP-1, GIP, PYY, ghrelin, glucagon, insulin, leptin, and pancreatic polypeptide concentrations by fluorescent assay. VAG, SG, RYGB, and BAL + VAG significantly reduced body weight 30 and 90 days after surgery. BAL alone induced temporal weight reduction observed after 30 days, reversed after 90 days. Calories intake was reduced at the first half of the observation period in all groups. Fluid intake was reduced in all groups except SG and BAL. Enterohormone profile for BAL + VAG was comparable to SG and RYGB but not BAL. VAG and BAL + VAG but not BAL alone maintain weight reduction, alimentary intake changes, and enterohormone release after long-term observation. VAG may improve the effectiveness of bariatric procedures for obesity treatment in clinical practice.

The Phantom Satiation Hypothesis of Bariatric Surgery

The excitation of vagal mechanoreceptors located in the stomach wall directly contributes to satiation. Thus, a loss of gastric innervation would normally be expected to result in abrogated satiation, hyperphagia, and unwanted weight gain. While Roux-en-Y-gastric bypass (RYGB) inevitably results in gastric denervation, paradoxically, bypassed subjects continue to experience satiation. Inspired by the literature in neurology on phantom limbs, I propose a new hypothesis in which damage to the stomach innervation during RYGB, including its vagal supply, leads to large-scale maladaptive changes in viscerosensory nerves and connected brain circuits. As a result, satiation may continue to arise, sometimes at exaggerated levels, even in subjects with a denervated or truncated stomach. The same maladaptive changes may also contribute to dysautonomia, unexplained pain, and new emotional responses to eating. I further revisit the metabolic benefits of bariatric surgery, with an emphasis on RYGB, in the light of this phantom satiation hypothesis.

Neuroimaging of gastric distension and gastric bypass surgery

Several neuroimaging studies are presented, which derive from prior work on gastric distension. Using a nonsurgical approach, we inserted gastric balloons into rats, which led to a marked decrease in food intake that normalized at 8 weeks. Body weight, however, remained below controls, which encouraged pursuit of studies in humans. A gastric balloon was inserted in obese and lean subjects, and filled through a tube that led behind the subject with water to 0, 200, 400, 600, 800 mL, on different days prior to ingestion of a liquid meal. As gastric volume increased, intake decreased by about 40%. Stomach capacity was then investigated using a gastric balloon, by assessing subjective (maximal tolerance) and objective measures (gastric compliance). Obese individuals had a much larger stomach capacity than lean by both measures. Next, in a 2-month study, an indwelling gastric balloon was inflated to 400 mL for 1 month and deflated for 1 month in counterbalanced order. Body weight was reduced during the month when the balloon was inflated within the 2nd and 3rd week. The subsequent study involved fMRI in response to gastric distension of 0, 250, and 500 mL while the subject was in a scanner. Ratings of fullness, but not discomfort, increased at 500 mL. Amygdala and insula activation were associated with gastric distension. The amygdala, as part of the limbic system, is involved in emotion and reward, and the insula in interoception. The right amygdala activation was inversely related to BMI, consistent with greater gastric capacity at a higher BMI. The next fMRI study in obese and lean subjects used visual and auditory stimuli of high energy dense (ED) and low ED foods. Increased activation was observed in the midbrain, putamen, posterior cingulate gyrus, hippocampus, and superior temporal gyrus in the obese vs. lean group in response to high vs. low ED food cues. Several of these areas lie within the mesolimbic reward pathway, and greater activation to high ED foods in the obese, suggests they have increased reward-driven eating behavior. Lastly, an fMRI study using the same stimuli was conducted pre and post-gastric bypass surgery. There were postsurgical reductions in neural activity in mesolimbic areas including the prefrontal cortex, and to a greater degree for high ED than low ED cues, reflecting more normalized responses. Through the use of various methodologies, the stomach's influence on food intake, sensations of fullness, and brain activation is presented with suggestions for future research.

Repeated gastric distension alters food intake and neuroendocrine profiles in rats

The consumption of a large food bolus leads to stomach distension. Gastric distension potently signals the termination of a meal by stimulating gastric mechanoreceptors and activating neuroendocrine circuitry. The ability to terminate a meal is altered in disorders such as bulimia nervosa (BN), binge-eating disorder (BED) and certain subtypes of obesity in which large quantities of food are frequently ingested. When a large meal is consumed, the stomach is rapidly stretched. We modeled this rapid distension of the stomach in order to determine if the neuroendocrine abnormalities present in these disorders, including increased gastric capacit3y, leptin dysregulation, and alterations in neuropeptide Y (NPY), and proopiomelanocortin (POMC) expression, were influenced by the rapid stretch aspect of repeatedly consuming a large meal. To test the effects of repeated gastric distension (RGD) on neuroendocrine factors involved in energy homeostasis, a permanent intra-gastric balloon was implanted in rats, and briefly inflated daily for 4 weeks. Though body weights and daily food intakes remained equivalent in RGD and control rats, a significant delay in the onset of feeding was present during the first and second, but not the third and fourth weeks of inflations. Despite equivalent body weights and daily caloric consumption, RGD animals had significantly decreased leptin levels (p<0.05), and tended to have increased fasting arcuate NPY levels (p=0.08), which were suppressed more than control animals following food intake (control and RGD decreases from baseline were 184.95% and 257.42%, respectively). NPY expression in the nucleus of the solitary tract followed a similar pattern. These data demonstrate that the act of regularly distending the stomach can have effects on the regulation of energy balance that are independent from those related to caloric consumption, and may be related to disorders such as BN, BED, and certain types of obesity in which meal termination is impaired.