The role of extracellular mucus as a protective cap over gastric mucosal damage.

Topical application of hypertonic saline to a chambered gastric mucosa (ex vivo) resulted in the formation of a cap of mucus, fibrin, plasma, and cellular debris over the damaged regions. The role of this 'mucoid cap' in protecting the underlying mucosa from subsequent challenges with hypertonic saline was studied. In the control group, the repeated challenges with 1 M NaCl in 0.05 M HCl caused macroscopically visible gastric damage involving only 2% of the total glandular mucosa. In the test group, in which the mucoid cap was peeled off the mucosa after the first challenge with NaCl, there was significantly more mucosal leakage of albumin (p less than 0.05), and the macroscopically visible gastric damage progressively increased to involve over 14% of the total glandular mucosa by the end of the experiment (p less than 0.005). Histological analysis showed that the mucoid cap provided a protective layer, allowing for restitution of the epithelium and protection of the mucosa from the damaging effects of hypertonic saline. In the absence of this protective layer, the repeated exposure to hypertonic saline resulted in deep mucosal necrosis. These studies support the hypothesis that mucus released in response to acute damage plays an important role in protecting the underlying mucosa so that restitution of the epithelium can proceed.