Distribution of Insulin Like Growth Factor-1 (IGF-1) and its Receptor in the Intestines of the One-humped Camel (Camelus dromedarius)

The distribution of insulin-like growth factor-1 (IGF-1) and its receptor in the gut of the one-humped camel (Camelus dromedarius) were studied by immunohistochemistry and quantitative receptor autoradiography. IGF-1-IR cells occurred mainly in the lamina propria and epithelium of the small intestine, while in the large intestine positive cells were seen in the columnar cells of the epithelial layer of colonic glands. IGF-1 was also discernible in the muscularis externa of the intestines. Autoradiography revealed a higher concentration of receptors in the mucosa compared to the muscular layer. With regard to the mucosa, the highest density of receptors was discernible in the duodenum. Immunohistochemistry revealed the main sites of the receptors to be the lamina propria, epithelia of the crypts and the villi of intestines. Double immunofluorescence studies with combined antisera to IGF-I and its receptor showed that the ligand and its receptor usually occurred within the same cell in the mucosa. A few cells with varied profiles immunoreacted to either the ligand or the receptor but not to both. Cells with varied profiles immunoreacted to antiserum of the receptors but not to the ligand in the muscle layer. Thus IGF-1 might be acting on its receptor via both an autocrine and paracrine modes in the camel mucosa. In the muscularis layer, IGF-1 may be acting by different mechanisms. Our data demonstrate that unlike all other mammals studied, the camel contains a high concentration of IGF-1 receptors in the duodenal mucosa compared to other parts of the camel gut. It also possesses a higher concentration of the receptor in its mucosa compared to the muscle layer. We speculate that this might be a significant feature necessary for the regenerative ability of the duodenal mucosa in the one-humped camel.