RELATIONSHIP BETWEEN GASTRIC MUCUS SYNTHESIS, SECRETION AND SURFACE GEL EROSION MEASURED IN AMPHIBIAN STOMACH IN-VITRO

1. The layer of adherent mucus that protects the surface of the stomac h reflects a dynamic balance between biosynthesis of glycoprotein, sec retion of preformed mucus and erosion of the adherent gel layer, The p resent study is the first in which all these processes have been measu red concomitantly and was undertaken to define interrelationships betw een the three parameters. 2. A chambered sac preparation of amphibian gastric mucosa is described, Biosynthesis was determined by specific i ncorporation of radiolabelled sugars into purified glycoprotein, Mucus secretion was determined by measuring the thickness of the adherent g el and erosion of the surface layer was assessed from the appearance o f soluble mucin in the luminal solution. 3. 16,16-Dimethyl-prostagland in (PG) E-2 stimulated glucosamine incorporation by 10-fold, but did n ot alter the rate of incorporation of galactose, There was a rapid two -fold increase in the thickness of the adherent mucus layer but no cha nge in the rate of erosion, Dibutyryl-cAMP also stimulated mucus relea se but, unlike PG, increased glycoprotein labelling by galactose. 4. B oth distention or the application of a cholinergic agonist increased a dherent mucus thickness, Stimulation of mucus release in response to c arbachol was accompanied by a decrease in glycoprotein labelling by ga lactose, In contrast, the adrenergic agent noradrenaline decreased sec retion but did not influeuce labelling. 5. These results indicate that biosynthesis and secretion of gastric mucus are subject to differenti al regulation, Moreover, the profile of incorporation of sugars in res ponse to secretagogues also differs, indicating the need for caution w hen interpreting effects on glycoprotein biosynthesis.