Role of salivary mucin in the protection, of rat esophageal mucosa from acid and pepsin-induced injury

The mucosal defensive mechanisms of the esophagus against acid and pepsin r emain to be elucidated. In the present study, we investigated the contribut ion of the salivary mucin in maintaining the integrity of the esophageal mu cosa. When an everted esophageal sac, isolated from normal rat, was treated with N-acetyl-L-cysteine, a mucolytic agent, the amount of glycoprotein in the gel layer adherent to the epithelium was completely depleted and the s usceptibility of the mucosa against acidified pepsin-induced digestion incr eased. In sialoadenectomized rats, 7 days after extirpation, the amount of glycoprotein adherent to the esophageal epithelium was definitely reduced, and the esophageal mucosa was significantly vulnerable to acidified pepsin- induced digestion compared with the sham-operated rats. Induction of regurg itation of the gastric juices into the esophagus resulted in the developmen t of severe hemorrhagic esophageal lesions only in the sialoadenectomized r ats but not in the sham-operated rats. In conclusion, the glycoprotein in t he adherent gel layer in rat esophagus, which mainly derives from salivary glands, plays an important role in the preepithelial defense to maintain th e integrity of the esophageal mucosa against acid and pepsin.