A comparative study on the activity of lansoprazole, omeprazole and PD-136450 on acidified ethanol- and indomethacin-induced gastric lesions in the rat. 
1.  The proton pump inhibitors lansoprazole (LP) and omeprazole (OP) and the cholecystokinin (CCK)-receptor antagonist PD-136450 (PD) provide a broad spectrum of activities in their ability to inhibit gastric acid secretion and protect the stomach against ulcerogens.  In the present study, we investigated the protective effects of these compounds against gastric ulcers induced by acidified ethanol (AE) and indomethacin.  2.  Both AE (60% ethanol in 150 mmol/L HCl, 1 mL/rat) and indomethacin (30 mg/kg) produced gastric haemorrhagic lesions in the rat 1 and 6 h after oral administration, respectively.  3.  The gastric mucosal protective effects of LP (1-20 mg/kg), OP (0.5-10 mg/kg) and PD (1-20 mg/kg), administered either orally or subcutaneously (s.c.)  30 min before the administration of AE or indomethacin, were dose dependent against both models of ulcer induction.  4.  To determine whether the cytoprotective effect of LP, OP and PD (each 10 mg/kg) was mediated by endogenous prostaglandins (PG), indomethacin (10 mg/kg, s.c.)  was administered 15 min before AE to inhibit prostanoids biosynthesis.  Indomethacin reduced the cytoprotective effects of OP, but not LP, administered either orally or s.c.  Indomethacin reduced the cytoprotective effect of PD administered orally, although the effect was much less significant than when PD was administered s.c.  The results exclude the role of PG in mediating the protective effects of LP, whereas the possibility exists for PG to have a role in mediating the protective effects of OP and PD.  5.  To investigate the possible involvement of endogenous nitric oxide (NO) in the cytoprotective action of LP, OP and PD, we treated rats with a selective inhibitor of NO synthesis, namely NG-nitro-L-arginine methyl ester (L-NAME; 25 mg/kg, s.c.).  Administration of L-NAME 15 min prior to LP, OP or PD (each 10 mg/kg) orally or s.c.  and challenge with AE or indomethacin did not significantly increase the degree of the ulcer index and L-NAME was not able to antagonize the protective effects of LP, OP and PD, thus excluding the role of NO in mediating the protective effects of these drugs.  However, the effects of PD in reducing the indomethacin-induced ulcer index were less significant in the presence than the absence of L-NAME (P < 0.05 vs P < 0.001, respectively), suggesting a role for NO.  6.  In conclusion, the results of the present study suggest that LP and OP are equally effective against AE- as well as indomethacin-induced gastric ulcers and were more potent than PD in protecting the stomach against ulcer formation.  Lansoprazole, OP and PD bring about their cytoprotective action through the reduction of acid secretion and some other unknown mechanisms.  However, OP and PD may exert their cytoprotective action through PG and NO pathways.