Immunoreactive epidermal growth factor in mouse digestive organs. Use of a sensitive enzyme immunoassay

A sandwich enzyme immunoassay (ELISA) system for mouse epidermal growth factor (EGF), which has a high sensitivity (500 fg/tube), has been established. It makes it possible to measure minute amounts of immunoreactive EGF in various mouse tissue without pretreatment. The immunoreactive EGF concentrations in digestive tissues of adult mice were much lower than previously reported. A significant sex difference was detected not only in the submandibular gland, but also in the oesophagus and forestomach. Although sialoadenectomy decreased the immunoreactive EGF contents in the alimentary tract to 4.2-23.8% of the pre-operative levels, the duodenal immunoreactive EGF was unaffected. Positive immunostaining was observed in the submandibular and sublingual gland, but not in the other digestive tissues, including the duodenum. These data implied that most of the EGF in the digestive tissues was derived mainly from the saliva and that a small amount of endogenous EGF existed in the duodenum. The physiological role of exogenous salivary EGF in the alimentary tract and the origin of endogenous duodenal EGF are discussed.