The effects of chrysin and pinostrobin, two flavonoids isolated from Teloxys graveolens leaves, on isolated guinea-pig ileum

The pharmacological effects of pinostrobin and chrysin obtained from the aerial parts of Teloxys graveolens (Chenopodiaceae) were evaluated using isolated in vitro guinea-pig ileal smooth muscle. Both flavonoids inhibited the contractions evoked by high concentrations of potassium. The potency of the relaxant effect was determined by measuring the capacity of each product in reducing the phasic and the slower sustained tonic contractile responses induced by depolarization with 60 mM K+. Concentrations up to 5 x 10(-7) M of pinostrobin and 1 x 10(-7) M of chrysin induced a non-competitive depression of responses to Ca2+ in ileum preparations bathed in a Ca2+-free, high K+ medium. Both compounds produced a rightward displacement of the concentration-response curves to Ca2+ with a concentration-depend ant increase of EC50 and a decrease of the maximal response. Examination of the inhibitory effect produced by these flavonoids on the phasic component of contractile response evoked with K+ and on the contraction induced with caffeine, led to propose a different intracellular mechanism of action used by these compounds. The results obtained led us to conclude that the previously detected relaxant effect of Teloxys graveolens crude extract is due in part, to the presence of chrysin and pinostrobin, which inhibit intestinal smooth muscle contractions by means of a calcium-mediated mechanism. Since the modulation of calcium fluxes in the mucosal epithelium may play a role in antidiarrheal drug action, the observed effects in vitro could in the same way explain the popular use of the plant for the treatment of diarrhea.