Cistus incanus and Cistus monspeliensis inhibit the contractile response in isolated rat smooth muscle

The lyophilized aqueous extracts from Cistus incanus L. (CI) and Cistus monspeliensis L. (CM) collected in Sicily were studied in order to evaluate their myorelaxant activity by using isolated smooth muscle of rat ileum and rat aorta. Both CI and CM extracts concentration-dependently inhibited the contractile response to acetylcholine (ACh), phenylephrine (PE) and to 100 mM KCl. The concentration-contraction curves to ACh in ileum and to PE in aorta, were displaced to the right by Cistus extracts in a non-competitive manner, with a depression of the maximum contractile response. The EC50 (microg/ml) of CM and CI were: ileum/KCl, CM 457+/-99, CI 681+/-80; ileum/ACh 100 microM, CM 297+/-66, CI 335+/-41; aorta/KCl, CM 360+/-21, CI 843+/-36; and aorta/PE 10 microM, CM 287+/-33, CI 451+/-58. The two extracts resulted almost equi-active in ileum, whereas CM was more active than CI in aorta. These data indicate that Cistus extracts act as spasmolytic on intestinal and vascular smooth muscle. The antagonism they exert on ACh-, PE- and KCl-evoked contractions seems to be functional, because it is not specifically directed toward any particular receptor; furthermore, a calcium-antagonist activity seems unlikely, since the extracts are capable of completely block the contractile response to agonists.