The biochemical pharmacology of mucus

The effect of O-acetylsalicylic acid on lipid synthesis by guinea pig gastric mucosa in vitro

The aim of this work was to investigate the involvement of lipids as possible components of the gastric mucosal barrier by studying the synthesis and secretion of lipids by the epithelial cell lining of gastric mucosa and the effect of salicylate on these processes. O-Acetylsalicylic acid reversibly reduced in vitro incorporation of [U-14C]acetate and of DL-[2-14C]mevalonic acid into lipids by isolated epithelial cells and by intact mucosa of guinea pig stomach, indicating reversible inhibition of lipid synthesis by the tissue in the presence of the drug. Inhibition of incorporation of both precursors into total lipids, into their fatty acid components, and into cholesterol is demonstrated.

Biosynthesis of proteins by human gastric mucosa in vitro

Incorporation of L-[U-14C]leucine and of D[U-14C]glucose into proteins of fresh human gastric mucosa in vitro was studied after incubation of homogenized tissue and of intact mucosal pieces. CsCl centrifugation was used to separate high-density mucus glycoproteins from other mucosal proteins, and the macromolecular nature of radioactive mucosal glycoprotein fractions was confirmed by SDS/polyacrylamide-gel electrophoresis and autoradiography of the polyacrylamide gels. In all experiments a substantial proportion of total incorporated radioactivity was associated with gastric-mucosal glycoprotein fractions (CsCl fraction L3), indicating their biosynthesis. Radioactivity of these fractions was shown to co-chromatograph with carbohydrates when fractionated either directly or after reduction and alkylation (1) Sephadex G-200 chromatography in the excluded fractions and (2) by DEAE-cellulose ion-exchange chromatography. On incubation of intact mucosa, the major portion of radioactivity associated with the glycoprotein fractions of both leucine- and glucose-labelled specimens was secreted into the mucosal media during the course of the experiment. It is suggested that biosynthesis of mucus in vivo by gastric mucosa may be associated with rapid secretion of the synthesized macromolecules into the lumen of the stomach and that investigations of the metabolic processes within the mucosa should consider the products of secretion of the tissue. Incorporation of L-[U-14C]leucine implies biosynthesis of the polypeptide components of the macromolecules.

Defects in prostaglandin synthesis and metabolism in ulcer disease

Ulcers occur because of an imbalance between mucosal protective resistance and damaging luminal factors, allowing the latter to predominate. The primary injurious elements are acid and peptic activity. Bile reflux, drugs, and gastroduodenal stasis may alter the luminal milieu and act together with acid-peptic activity to produce injury, weaken mucosal resistance, or both. Since prostaglandins modulate several key mucosal protective mechanisms, and since some exogenous prostaglandins and their derivatives accelerate peptic ulcer healing, it seems plausible that prostaglandin deficiency may contribute to the development of peptic ulcers. At the present time, however, evidence for this postulate is mostly indirect and can be summarized as follows: (1) Defects of mucosal protective mechanisms modulated by prostaglandins have been found in different forms of ulcer disease. Such defects include impaired duodenal bicarbonate secretion, deficient secretion or accelerated degradation of mucus, and reduced mucosal cell proliferation. (2) Drugs that inhibit cyclooxygenase, the key enzyme in tissue prostaglandin synthesis, have ulcerogenic activity. Presumably, in this situation, reduced prostaglandin production renders the mucosa more vulnerable to the action of acid and pepsin, or reduces the capability of the mucosa to repair itself. (3) Decreased mucosal prostaglandin synthesis or prostaglandin content has been found in patients with ulcer disease. Several studies have provided quantitative evidence of disturbed prostaglandin metabolism in some forms of ulcer disease. These studies are of high interest, but they need to be interpreted with caution given the present scientific debate regarding the physiological role of different prostanoids, as well as uncertainty as to the specific cellular source of prostaglandins in gastroduodenal mucosa.

Prostaglandin metabolism in peptic ulcer disease

Over the past decade, the physiological role of prostaglandins synthesized by the gastroduodenal mucosa has been the subject of intense research. Unfortunately, progress has been slow. Methodological problems in the identification and measurement of different prostanoids, as well as technical difficulties in performing definitive experiments, are largely to blame. Prostaglandins are not stored in tissue, can be rapidly synthesized and metabolized during tissue analysis, and appear to have multiple and sometimes conflicting biological actions on the mucosal tissues. Given these challenging problems at the biochemical and cellular levels, it is not surprising that relatively few studies have addressed potential defects in prostaglandin synthesis in patients with ulcer disease. Furthermore, the results obtained by these human studies are not always comparable because of the diverse methodological approaches chosen by different investigators. The evidence so far obtained suggests, though not conclusively, that mucosal prostaglandins play a role in the pathogenesis of ulcer disease. The most plausible hypothesis holds that defects in prostaglandin synthesis, metabolism or action on target tissues either weaken mucosal resistance to luminal acid-peptic activity or impair mucosal repair, leading to the development of chronic peptic ulcer.

Effects of fasting on mucus glycoprotein biosynthesis in rat stomach

Biosynthetic activity of gastrin mucus glycoprotein in rats after fasting for 24 and 72 hr was studied by the organ culture technique. Fasting produced a slight reduction in gastric mucus glycoprotein biosynthesis in the corpus and antrum (about 70-90% of fed rats). Sulfation of gastric mucus glycoprotein was restrained in the corpus (18% in control for 72 hr).