A lyophilized aqueous extract of Maytenus ilicifolia leaves inhibits histamine-mediated acid secretion in isolated frog gastric mucosa

Lyophilized aqueous extract of Maytenus ilicifolia leaves (LAEMIL) is commonly used in Brazilian folk medicine in the treatment of dyspepsia as well as gastric ulcers. We have investigated the effect and the possible mechanism of action of the LAEMIL on acid secretion in isolated frog gastric mucosa incubated in an Ussing chamber. It was observed that LAEMIL (7-28 mg%) as well as cimetidine (125-4,000 muM), a well-known histamine H-2 receptor antagonist, decreased basal acid secretion in a concentration-dependent manner. Similarly to cimetidine (190 muM), LAEMIL (21 mg%) also inhibited gastric acid secretion induced by increasing concentrations of histamine (50-800 muM). The EC50 values for histamine alone and histamine in the presence of LAEMIL or cimetidine were 94.6 muM (71.1-125.9 muM), 244.9 muM (209.4-286.4 muM) and 142.2 muM (23.6-855.0 muM), respectively. LAEMIL, histamine and cimetidine were effective on acid secretion only when added to the serosal surface of the mucosa. Furthermore, simultaneous addition of LAEMIL and cimetidine at concentrations, per se, ineffective, caused a 16% reduction in the basal acid secretion [from 8.3+/-0.3 to 6.9+/-0.2 muEq g(-1) (15 min)(-1), n=4]. Although effects such as inhibition of histamine biosynthesis and/or histamine release can not be ruled out, our data suggest that LAEMIL, like cimetidine, reduces acid secretion in the isolated frog gastric mucosa by antagonising histamine H-2 receptors.