Prostaglandin protection against ethanol-induced gastric injury: regulatory effect on the mucus glycoprotein metabolism.

Effects of ethanol and prostaglandin on the metabolic processes of gastric mucosal cells have been evaluated by studying the biosynthesis and intra- and extracellular distribution of mucus glycoprotein. The rat gastric mucosal cell suspensions were subjected to a short-term tissue culture in the presence of 0-1.5 M ethanol and 0-100 ng/ml 16,16-dimethyl prostaglandin E2 (DMPGE2), using [3H]proline and [3H]palmitic acid as markers of mucin apoprotein synthesis and modification. Ethanol at concentrations of 0.02-0.1 M stimulated the glycoprotein synthesis, but the product was 2-3 times more extensively and rapidly degraded by pepsin than the glycoprotein synthesized in the absence of ethanol. Higher concentrations of ethanol (0.1-1.5 M) caused a marked reduction in the glycoprotein synthesis and a depletion of the intracellular mucus glycoprotein stores, and at 1.5 M ethanol the synthetic processes ceased to function. When the incubated tissue cultures were challenged with DMPGE2, the highest synthetic and secretory stimulation was achieved at 10 ng/ml. The peptic susceptibility of the glycoprotein synthesized in the prostaglandin-enriched culture was somewhat lower than that of controls, and the proportion of the undegraded glycoprotein remaining after 22 h of digestion was significantly higher. Furthermore, the intracellular compartments were not depleted of mucus glycoprotein and the amount of the mucin apoprotein precursor increased to about 30%. Addition of DMPGE2 prior to ethanol treatment resulted in the stabilization of cellular processes and the cells responded as if ethanol was not present in the medium. Moreover, the intracellular stores of mucus glycoprotein were not depleted and the secretory rate was moderately elevated. The regulatory effect of DMPGE2 on the glycoprotein synthesis and distribution was significant, but diminished with increasing amounts of ethanol in the medium. The results suggest that DMPGE2 imposes a stabilizing effect on the secretory processes and controls the mucus glycoprotein synthesis, but the extent of this protective action against ethanol is limited and depends upon the concentration of ethanol penetrating the mucosal cells.