RESUMO
The decoction of Dalbergia monetaria L. is popularly used in Brazil for the treatment of gastric ulcer and the lyophilized aqueous extract (LAE) of D. monetaria has significant anti-ulcerogenic activity and inhibits gastric ulcer lesions induced by pylorus-ligature, ethanol and hypothermic-restraint stress. This work was conducted to identify the antiulcerogenic mechanisms of action of the LAE of D. monetaria. We analysed the effect of the LAE on prostaglandin E2 (PGE2) synthesis and on the characteristics (pH, volume and total acid content) of gastric juice. The antagonism between the LAE and histamine or carbachol was also analysed. The LAE increased gastric mucosal PGE2 synthesis compared with control (89.7+/-21.5 and 52.6+/-11.8 pg mg(-1), respectively) as assayed by enzyme immunoassay in the rat stomach. The LAE reduced the total acid content of gastric juice, but did not modify pH or gastric volume significantly, in Shay rats. Dose-response curves to histamine were shifted to the right in guinea-pig isolated right atria (pD2 values were 5.77+/-0.2 and 5.42+/-0.3, respectively, in the absence and presence of the LAE), with a significant reduction in maximum response (140+/-15.1 and 98+/-13.0, respectively). The same effect was observed when the agonist was isoprenaline. The LAE had no effect on the dose-response curve to carbachol in rat fundus strips. Thus, the protective effect of the LAE on induced gastric lesions might be because of synergistic effects, e.g. increased PGE2 synthesis and antagonism of H2 histamine and beta-adrenergic receptors, reducing gastric acid secretion. Increased PGE2 synthesis results in increased protection, and antagonism of H2 histamine and beta-adrenergic receptors reduces aggressive factors against the gastric mucosa.