Mechanisms of oesophageal mucosal defence.

The integrity of the oesophageal mucosa depends upon an equilibrium between aggressive factors, predominantly acid and pepsin, and protective mechanisms. Protective mechanisms operate within the oesophageal mucosa as pre-epithelial, epithelial and post-epithelial defences. Only the protective components of the oesophageal pre-epithelial defence can be tested in vivo in humans. It has been recently demonstrated that human oesophageal submucosal glands elaborate mucous secretion rich in bicarbonate and non-bicarbonate buffers, mucin, prostaglandin E(2), epidermal growth factor (EGF) and transforming growth factor alpha (TGFalpha). This oesophageal secretion, accompanied by similarly protective factors within the swallowed saliva, defines the protective potential of the oesophageal pre-epithelial defence that exists in the form of a mucus-buffer layer covering the oesophageal mucosa and which retards the back-diffusion of hydrogen ions. It has also been demonstrated that patients with severe erosive reflux oesophagitis exhibit qualitative impairment in both the salivary and oesophageal components of the oesophageal pre-epithelial defence. Furthermore, patients with endoscopically negative gastro-oesophageal reflux disease have a significantly stronger oesophageal pre-epithelial defence than patients with erosive reflux oesophagitis. On the other hand, African-Americans, who are less likely to develop erosive reflux oesophagitis, have a stronger oesophageal pre-epithelial defence than do Caucasians. The salivary component of the oesophageal pre-epithelial defence can be enhanced by mastication and the administration of cisapride, whereas oesophageal secretion can only be significantly augmented by cisapride.