Effects of bovine alpha-lactalbumin on gastric defense mechanisms in naive rats.

We recently investigated the effects of the major proteins in cow's milk on gastric mucosal injuries in rat ulcer models. We found that alpha-lactalbumin (alpha-LA) has marked preventive effects against gastric mucosal injuries and that prostaglandin (PG) synthesis may contribute to these effects [Matsumoto et al., Biosci. Biotechnol. Biochem., 65, 1104-1111, 2001]. In this study, we investigated the effects of alpha-LA on several defense mechanisms of gastric mucosa by evaluating gastric PGE2 content, gastric mucin content, gastric luminal pH, gastric fluid volume, and gastric emptying in naive rats. Oral administration of alpha-LA (200, 500, and 1000 mg/kg) elevated endogenous PGE2 levels in gastric tissue and increased the gastric mucin contents of both the gastric fluid and the adherent mucus gel layer. In addition to these PG-related responses, alpha-LA also caused PG-independent responses such as elevation of gastric luminal pH, increase in gastric fluid volume, and delay in gastric emptying. These responses were observed to be dose-dependent (200-1000 mg/kg of alpha-LA). Thus, we demonstrated that alpha-LA enhances both PG-dependent and PG-independent gastric defense mechanisms in naive rats. Both of these mechanisms are probably involved in its gastroprotective action.