Mucosal permeability regulates receptor binding of luminal epidermal growth factor in the adult rat intestine

Epidermal growth factor (EGF) stimulates repair in the damaged intestine, but its role in the normal intestine is not clear. Because EGF receptors are found on the basolateral surface but not the luminal surface, we hypothesized that mucosal permeability regulates EGF binding. Adult male rats were divided into 3 groups, one that was fed normal chow (the control), one that was starved for 4 days, and one that was given methotrexate (MTX) intragastrically (10 mg/kg/day for 3 days). The rats were sacrificed and everted sacks of the jejunum were made and incubated in EGF solution. Western blot analysis of mucosal homogenates showed that the amount of phosphotyrosyl EGF receptor in the starved and MTX-treated groups was, respectively, about 1.5 times and 2 times that in the control group. The mucosal permeability in the starved and MTX treated groups also increased and varied directly with the amount of phosphotyrosyl EGF receptor. These results suggest that in the adult rat intestine, luminal EGF may play a role only under tissue damage, where enhanced permeability permits the EGF to pass through the mucosa and bind to its receptor on the basolateral membrane.