Effects of fasting on mucus glycoprotein in rat stomach

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 remain to be elucidated. In the present study, we investigated the contribution of the salivary mucin in maintaining the integrity of the esophageal mucosa. 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 susceptibility of the mucosa against acidified pepsin-induced digestion increased. 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 regurgitation of the gastric juices into the esophagus resulted in the development of severe hemorrhagic esophageal lesions only in the sialoadenectomized rats but not in the sham-operated rats. In conclusion, the glycoprotein in the adherent gel layer in rat esophagus, which mainly derives from salivary glands, plays an important role in the preepithelial defense to maintain the integrity of the esophageal mucosa against acid and pepsin.

Mucin output in ileal digesta of pigs fed a protein-free diet

Daily outputs of mucin in ileal digesta were estimated in three barrows fed a protein-free diet while administered either saline (SAI) or a complete amino acid mixture (AAI) intravenously. The water soluble-ethanol precipitable fraction of ileal digesta (crude mucin; CM) was used to estimate the composition of mucin in ileal digesta. This fraction exhibited a carbohydrate composition characteristic of mucin and had a high threonine, serine and proline content (40 mol/100 mol). The proportions of soluble gastric and intestinal mucins, approximately 27 and 73%, respectively, were estimated from the N-acetylglucosamine (GlcNAc)/N-acetylgalactosamine (GalNAc) ratio in CM. The daily outputs of soluble mucin, 2.75 and 3.41 g/day from SAI and AAI pigs (p = 0.13), respectively, were determined from the GalNAc outputs in CM, assuming the above contributions of gastric and intestinal mucins. The estimated soluble mucin outputs accounted for more than 99% of the fucose, galactose, GalNAc and GlcNAc in CM. Total mucin outputs in ileal digesta, 5.32 and 5.65 g/day from SAI and AAI Pigs (p = 0.24), respectively, were determined from the total GalNAc output in digesta, assuming soluble and insoluble mucin had similar compositions. Based on these outputs, mucin represented approximately 30, 7 to 22, 15 and 11% of the endogenous threonine, proline, serine and protein, respectively, in ileal digesta. Approximately 74, 76, 100 and 53% of the fucose, galactose GalNAc and GlcNAc, respectively, in ileal digesta from pigs in this study was attributed to mucin. The results from this study demonstrate the importance of mucin as a source of some endogenous amino acids and carbohydrates.

A separating method for quantifying mucus glycoprotein localized in the different layer of rat gastric mucosa

A method was devised for separating rat gastric mucosa into three layers each containing a different mucin species. The mucus gel (first layer) was removed by stirring the gastric mucosa in a solution of phosphate-buffered saline containing 2% N-acetylcysteine. The surface mucosa (second layer), rich in surface mucus cells, was then separated from the deep mucosa (third layer) containing mucus neck cells, by scraping with forceps. The effectiveness of this method was confirmed by light microscopical observation after GOCTS-PCS (dual staining by the galactose oxidase-cold thionin Schiff method and paradoxical concanavalin A method) and AB-PAS staining (dual staining with alcian blue and the periodic acid Schiff method). The fixed specimen of scraped mucus and cell debris was rich in AB-PAS and GOCTS positive mucus, but was hardly stained by PCS, indicating mucus derived from surface mucus cells to have been efficiently recovered from this preparation. The residual mucosa could be stained by PCS but hardly at all by AB-PAS or GOCTS. The lyophilized powder specimens obtained from the three different layers of rat gastric mucosa were used to extract and quantify mucus glycoprotein (mucin). This was done to examine changes in mucin content in the three layers of gastric mucosa one hour following the oral administration of 20% ethanol or 0.35 N hydrochloric acid, both mild irritants. Mucin content was noted to significantly increase in the first layer but hardly at all in the second layer. In the third layer, it decreased significantly by 0.35 N hydrochloric acid, but changed only slightly by 20% ethanol administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of treatment with smectite on gastric and intestinal glycoproteins in the rat: a histochemical study

A histochemical study was carried out to evaluate the changes that occur in the glycoproteins of the rat digestive tract following short term treatment with a clay smectite. Staining with the usual methods for detecting complex carbohydrates and with lectin conjugates (Con A, LTA, PNA, SBA and WGA) showed that the stomach was the susceptible organ. Increased staining with LTA and SBA, together with a decrease in the abundance of sulphate groups in the upper mucous neck cells, was observed after the clay treatment. Such treatment induced only slight changes in jejunal and colonic glycoproteins while no modification was observed in the colon. These data suggest that the content of mucus-producing cells could be affected by smectite, even following short-term treatment.