The effects of a nitric oxide (NO)-releasing derivative of aspirin, NCX-4016, on gastric functional and ulcerogenic responses in rat stomachs were examined in comparison with those of aspirin. Topical application of aspirin (80 mM) to the stomach markedly decreased transmucosal potential difference and slightly increased luminal pH (acid back-diffusion) with minimal effect on mucosal blood flow, whereas NCX-4016 caused a marked increase in mucosal blood flow with no effect on potential difference and pH. Aspirin itself was ulcerogenic, causing damage in the mucosa when administered p.o., and it markedly potentiated gastric ulcerogenic response to hypothermic stress (28 degrees C-30 degrees C) with no effect on acid secretion when given s.c. NCX-4016, however, was not ulcerogenic by itself, did not modify the ulcerogenic response to stress and even showed a dose-dependent protection against HCl/ethanol-induced gastric lesions. When NCX-4016 was given intragastrically to pylorus-ligated rats, a large amount of NO was detected in both gastric contents and serum. NCX-4016 administered either p.o. or s.c. produced an equipotent inhibition of mucosal PGE2 generation in the stomach, as compared with aspirin. In addition, both aspirin and NCX-4016 suppressed carrageenan-induced rat paw edema. These results suggest that, unlike aspirin, the NO-releasing derivative of aspirin NCX-4016 neither had a topical irritating action on the stomach nor exerted a worsening effect on gastric ulcerogenic response to stress, but rather provided gastric protection against ethanol, despite inhibiting cyclo-oxygenase activity and showing anti-inflammatory action much as aspirin does. NCX-4016, probably by releasing NO, exerted protective effects that counteracted the potential damaging effects of cyclo-oxygenase inhibition.