A comparison of the effect of growth factors on intestinal function and structure in short bowel syndrome

Epidermal growth factor (EGF) and Insulin like growth factor-1 (IGF-1) increase substrate absorption beyond the normal adaptive response after massive small bowel resection in the rat. However, the mechanism for this response is unknown. This study was designed to evaluate the ultrastructural features of the rat small intestine epithelium after exposure to EGF and IGF-1 and correlate any changes with a possible hypothesis regarding the mechanism for the increased absorption.

Male Sprague-Dawley rats underwent an 80% small bowel resection and jejunostomy tube placement. Seven days later an osmotic pump placed subcutaneously and containing the test substance was connected to the jejunostomy tube. The rats were assigned to one of three groups: group 1 received normal saline (control, n = 5); group 2 received EGF at 150 microg/kg/d (n = 5); and group 3 received IGF-1 at 20 mg/kg/d (n = 5). After a 14-day infusion, a portion of mid-small bowel was resected for light and electron microscopic evaluation from each of the animals. The following features were compared between the groups: villous length, crypt length, villous-crypt ratio, villi per millimeter mucosa, goblet cell distribution, eosinophilic infiltrates, number and distribution of organelles, length of microvilli, and completeness of microvillous surface.

Ultrastructurally, the bowel epithelium was well preserved in all animals. There were no objective ultrastructural differences between the controls and growth factor-exposed animals. The mean villous-crypt ratio, mean number of villi per millimeter of mucosa (cross section), and mean microvillous height were not significantly different among the groups. However, there was a subjective increase in the number of lysosomes in the enterocytes exposed to EGF and IGF-1.

Administration of EGF and IGF-1 after massive small bowel resection does not appear to significantly alter the small intestine epithelial ultrastructure when compared with the control group. The increase in lysosomes in some of the enterocytes of the animals exposed to growth factors may be important because this finding was not seen in any of the control electron photomicrographs. Studies to evaluate enterocyte gene and protein expression are necessary to determine the mechanism of EGF and IGF-1 enhancement of substrate absorption beyond intestinal adaptation.