Ileal Smooth Muscle Thickness is Greater in Young Obese Zucker Rats

Abstract

Obesity is a risk factor for many pathologies including heart disease, type 2 diabetes and certain types of cancers. At this time little is known about how obesity effects the morphology of the small intestine or gut. The purpose of this study was to determine what morphological differences exist in the smooth muscle of the small intestine, between lean and obese Zucker rats. We hypothesized that the thickness of the circular and longitudinal muscle layers of the small intestine from obese Zucker rats would be greater compared to their lean counterparts. Ileum and jejunum from lean and obese Zucker rats were harvested, fixed in buffered formalin overnight, processed, and embedded in paraffin. Thin cross sections of the tissues were mounted on slides, stained with H&E followed by analyses of longitudinal and circular smooth muscle layer thicknesses using digital photos and FIJI/IMageJ software (version 1.5). Smooth muscle thickness data was exported from an Excel document and statistics performed utilizing GraphPad Prism (version 6.0). In addition, ileum from lean and obese Zucker rats was harvested, bisected lengthwise with the lacteals facing up, and fixed in 4% PFA overnight and then washed with sucrose solutions. The ileum tissues were pinned onto 6‐well silicone plates and strips of villi (1‐2 thick) were cut under a dissecting microscope. The villi strips were incubated with a LYVE‐1 antibody to identify lymphatic endothelial cells of the lacteals and a PECAM‐1 antibody to label microcirculation within the villi. Longitudinal and circular smooth muscle layers, identified in the ileum with H&E staining, were significantly thicker in 8‐week old obese Zucker rats compared to lean rats. No significant differences in smooth muscle thickness were observed in 12‐week or 26–32‐week old obese versus lean rats in either the ileum or the jejunum. Histological data obtained from the small intestine partially supports the hypothesis that intestinal smooth muscle layer thickness in obese juvenile Zucker rats was greater, but only at the 8‐week time point. Preliminary immunolabeling with LYVE‐1 positively identified the structure of the lacteal, while the PECAM‐1 labeling was strong within the microvasculature of the villi. Although additional studies with human tissue, e.g., samples derived from intestinal biopsies or surgical resection, are required to understand the biomedical significance of our findings, our data raise the possibility that for humans at a young age obesity may cause structural changes in the small intestine.Support or Funding InformationThis work was supported by an APS IOSP Undergraduate Summer Research Fellowship IOS‐1238831.