The positive inotropic effect of ethanol extract of Lepidium apetalum in beating rabbit atria

Abstract

In the present study, the positive inotropic effects of ethanol extract of Lepidium apetalum (ELA) and possible mechanisms responsible for this effect were investigated in beating rabbit atria. ELA (5 x 10−4 g/ml) significantly increased atrial stroke volume, pulse pressure, and cAMP efflux in perfused beating rabbit atria. These effects were not altered by pre-treatment with diltiazem (5 x 10−6 M) or verapamil (1 x 10−6 M), L-type Ca2+ channel blockers. In addition, ELA-induced increases in atrial stroke volume, pulse pressure, and cAMP were not inhibited by pre-treatment of staurosporine (1 x 10−6 M), a non-specific protein kinase inhibitor. ELA markedly increased K+ concentration in beating atria-derived perfusate. Helveticoside (2 x 10−5 M), a well known digitalis-like cardiac glycosidic constituent of ELA, also increased atrial stroke volume and pulse pressure without changes in cAMP efflux, which were partially inhibited by pre-treatment with diltiazem, verapamil, or staurosporine, respectively. These results suggest that ELA-induced positive inotropic effect in beating rabbit atria might due to digitalis-like activity of helveticoside and partially be related with the increase in cAMP.