hydro-ethanolic extract of portulaca oleracea affects beta-adrenoceptors of guinea pig tracheal smooth muscle

the stimulatory effect of the extract of portulaca oleracea (p. olerace) on β-adrenoceptor of tracheal smooth muscle was examined. to examine β-adrenoceptor stimulatory effect, concentration response curve to isoprenaline was obtained in pre-contracted tracheal smooth muscle in the presence of three concentrations of aqueous-ethanolic extract, propranolol and saline. values of ec50 (the effective concentration of isoprenaline, causing 50% of maximum response) and dose ratio -1 (cr-1) were measured. this effect was tested in non-incubated tracheal smooth muscle (group 1) and incubated tissues with chlorpheniramine (group 2). concentration-response curves to isoprenaline in the presence of two higher concentrations of the extract in group 1 and all three concentrations in group 2 showed leftward shifts compared to isoprenaline curves produced in the presence of saline in both groups. ec50 obtained in the presence of propranolol was significantly higher than that of saline in both groups of experiments (p