AIM: This study investigated the mechanisms of protection afforded by the proton pump inhibitor lansoprazole against gastric injury induced by different non-steroidal anti-inflammatory drugs (NSAIDs) in rats. METHODS: Male Sprague-Dawley rats were orally treated with indomethacin (100 μmol/kg), diclofenac (60 μmol/kg), piroxicam (150 μmol/kg) or ketoprofen (150 μmol/kg). Thirty minutes before NSAIDs, animals were orally treated with lansoprazole 18 or 90 umol/kg. Four hours after the end of treatments, the following parameters were assessed: gastric mucosal PGE2, malondialdehyde (MDA), myeloperoxidase (MPO) or non-proteic sulfhydryl compounds (GSH) levels; reverse transcription-polymerase chain reaction (RT-PCR) of mucosal COX-2 mRNA; gastric acid secretion in pylorus-ligated animals; in vitro effects of lansoprazole (1-300 μmol/L) on the oxidation of low density lipoproteins (LDLs) induced by copper sulphate. RESULTS: All NSAIDs elicited mucosal necrotic lesions which were associated with neutrophil infiltration and reduction of PGE2 levels. Increments of MPO and MDA contents, as well as a decrease in GSH levels were detected in the gastric mucosa of indomethacin- or piroxicam-treated animals. Indomethacin enhanced mucosal cyclooxygenase-2 expression, while not affecting cyclooxygenase-1. At the oral dose of 18 μmol/kg lansoprazole partly counteracted diclofenac-induced mucosal damage, whereas at 90 μmol/kg it markedly prevented injuries evoked by all test NSAIDs. Lansoprazole at 90 μmol/kg reversed also the effects of NSAIDs on MPO, MDA and GSH mucosal contents, without interfering with the decrease in PGE2 levels or indomethacin-induced cyclooxygenase-2 expression. However, both lansoprazole doses markedly inhibited acid secretion in pylorus-ligated rats. Lansoprazole concentration-dependently reduced the oxidation of LDLs in vitro. CONCLUSION: These results suggest that, besides the inhibition of acid secretion, lansoprazole protection against NSAID-induced gastric damage depends on a reduction in mucosal oxidative injury, which is also responsible for an increment of sulfhydryl radical bioavailability. It is also suggested that lansoprazole does not influence the down-regulation of gastric prostaglandin production associated with NSAID treatment. AIM: This study investigated the mechanisms of protection afforded by the proton pump inhibitor lansoprazole against gastric injury induced by different non-steroidal anti-inflammatory drugs (NSAIDs) in rats. METHODS: Male Sprague-Dawley rats were orally treated with indomethacin (100 μmol / kg), diclofenac (60 μmol / kg), piroxicam (150 μmol / kg) or ketoprofen (150 μmol / kg). Thirty minutes before NSAIDs, animals were orally treated with lansoprazole 18 or 90 umol / kg. end of treatments, the following parameters were assessed: mucosal PGE2, malondialdehyde (MDA), myeloperoxidase (MPO) or non-proteic sulfhydryl compounds mRNA: gastric acid secretion in pylorus-ligated animals; in vitro effects of lansoprazole (1-300 μmol / L) on the oxidation of low density lipoproteins (LDLs) induced by copper sulphate. RESULTS: All NSAIDs elicited mucosal necrotic lesions which were associ ated with neutrophil infiltration and reduction of PGE2 levels. Increments of MPO and MDA contents, as well as a decrease in GSH levels were detected in the gastric mucosa of indomethacin- or piroxicam-treated animals. Indomethacin enhanced mucosal cyclooxygenase-2 expression, while not affecting cyclooxygenase-1. At the oral dose of 18 μmol / kg of lansoprazole partly counteracted diclofenac-induced mucosal damage, but at at 90 μmol / kg it markedly adjusted of evoked all of the NSAIDs. Lansoprazole at 90 μmol / NSAIDs on MPO, MDA and GSH mucosal contents, without interfering with the decrease in PGE2 levels or indomethacin-induced cyclooxygenase-2 expression. However, both lansoprazole doses markedly inhibited acid secretion in pylorus-ligated rats. Lansoprazole concentration-dependently reduced the oxidation of LDLs in vitro. CONCLUSION: These results suggest that, besides the inhibition of acid secretion, lansoprazole protection against NSAID-indu ced gastric damage depends on a reduction in mucosal oxidative injury, which is also responsible for an increment of sulfhydryl radical bioavailability. It is also suggested that lansoprazole does not affect the down-regulation of gastric prostaglandin production associated with NSAID treatment.