Adjustable Gastric Banding and Its Effects on Postprandial Glucose Metabolism Independent of Weight Loss

• Disposition Index [ Time Frame: Change compared to baseline 12 weeks after intervention ] [ Designated as safety issue: No ]
  Insulin sensitivity which measures the overall ability of insulin to stimulate glucose disposal and inhibit glucose production will be calculated from plasma glucose and insulin concentrations using the "oral" glucose minimal model. Beta-cell responsivity indices will be calculated using plasma glucose and C-peptide concentrations using the oral C-peptide minimal model. The appropriateness of insulin secretion for the prevailing degree of insulin action is assessed by calculating the total disposition index (DItotal), which equals the product of insulin secretion and insulin sensitivity.
  
  

• Gastric emptying and intestinal transit [ Time Frame: change compared to baseline 12 weeks after intervention ] [ Designated as safety issue: No ]
  

The overall aim of this application is to determine the mechanism(s) by which common bariatric surgical procedures alter carbohydrate metabolism. Very often, resolution of diabetes occurs in the early post-operative period prior to the development of significant weight loss. It has been suggested that bariatric surgery alters insulin action but few studies have examined insulin secretion or postprandial glucose fluxes in such patients. At the present time, little is known about how the various bariatric surgical procedures alter glucose homeostasis. It is essential that the effect of bariatric surgery and meal size on these parameters be understood and accurately measured. Enteroendocrine secretion is affected by the rate of intestinal delivery of calories and may also be modulated by the enteric nervous system and the rate of direct delivery of nutrients to enteroendocrine cells. Direct measurement of intestinal transit is also an important part of understanding how bariatric surgery alters intestinal secretion of hormones that may alter glucose metabolism. The Oral and C-peptide Minimal Models when applied to C-peptide, glucose and insulin concentrations after ingestion of a standard labeled mixed meal can accurately measure insulin secretion and action. Subsequently, the disposition index provides a measurement of the appropriateness of insulin secretion for the prevailing insulin action. When coupled with established triple-tracer methodology, a mixed meal can be used to measure fasting and postprandial glucose fluxes. The present experiments will determine the mechanism of glucose lowering after adjustable gastric banding (AGB). AGB seems to be superior to medical therapy in type 2 diabetes. However, bariatric surgery was not compared to intensive efforts at weight reduction which itself ameliorates diabetes and cardiovascular risk. It is therefore unknown if the beneficial effects of AGB on glucose metabolism are related to weight-loss per se rather than a direct effect of AGB.