Rat gastric mucous gel layer contains sialomucin not produced by the stomach

The sialylated mucus components of the normal gastric mucosa and mucous gel layer of rats were studied by using various histochemical staining methods including Maackia amurensis II (MAL-II) and Sambucus nigra (SNA) lectins, alcian blue (AB) pH 2.5 -- periodic acid Schiff (PAS) and high iron diamine (HID) -- AB pH 2.5. The acidic and neutral mucins characterized by the AB-PAS staining were abundantly present in the mucous gel layer as well as in the gastric mucosa. The sialomucin characterized by HID-AB was barely found in either the mucous gel layer or the mucosa. The sialomucin positive to MAL-II and SNA, which react with the N-acetyl neuraminic acid residue linked to galactose via an alpha-linkage, was moderately detected only in the mucous gel layer, but not in the entire mucosal layer. Furthermore, in animals given surgery to form an esophageal fistula through which saliva was excluded or in animals subjected to salivectomy, the mucous gel layer stained with MAL-II and SNA lectins was markedly decreased. These results indicate that a part of the sialomucin containing-mucous gel layer covering normal rat gastric mucosa originates from the saliva and that MAL-II and SNA lectins are useful for detecting this specific sialomucin.