In vivo and in vitro analysis of the effect of various acid-secretion blockers on UDP-galactosyltransferase activities in rat gastric mucosa

Gastric mucus glycoprotein is important for the protection of gastric mucosa from acid. UDP-galactosyltransfer-ase (UDP-Gal-T) is a key enzyme for the synthesis of gastric mucus glycoprotein. In this study, we investigted the effects of five acid-secretion blockers, cimetidine, ranitidine, famotidine, roxatidine and omprazole on the UDP-Gal-T activity in rat gastric mucosa to clarify the interaction of the acid-secretion blocker and the gastric mucosal barrier. Intraperitoneal administration of these drugs to rat increased pH of the gastric mucosal suface and significantly decreased the gastric UDP-Gal-T activies. When we administered citrate phoshate buffer (pH 2) to the rat stomach to inhibit the change of gastric pH induced by the acid-secretion blockers, the effecer of famotidine, roxatidine and omeprazole on UDP-Gal T activties were abolished, but cimetidine and ranitidine significantly decreased the enzyme activiyty When we incubated the acid-secretion blockers with the homogenates of ral gastric mucosa, cimetidine and ranitidine significantly dereased UDP-Gal-T activites, whreas the other drugs showed no apparent influence on the enzyme sctivity. These findins suggest that the acid-secretion blockers decrease gastric mucin synthesis via the increase of the intragastric pH.In addition, among the acid-secretion blockers stydied here, cimetidine and rantidine also have direct inhibitory effects on the gastric UDP-Gal-T activity.

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