Aqueous-methanolic extract of sweet flag (<Emphasis Type="Italic">Acorus calamus</Emphasis>) possesses cardiac depressant and endothelial-derived hyperpolarizing factor-mediated coronary vasodilator effects

This investigation was aimed to probe the pharmacological base of medicinal use of Acorus calamus in ischemic heart diseases. Effect on heart parameters was studied in isolated rabbit heart while coronary vasodilator effect was studied in isolated bovine coronary arterial rings, suspended in tissue baths filled with Krebs solution, maintained at 37°C, aerated with carbogen and responses were measured on PowerLab data acquisition system. In Langendorrf’s perfused rabbit heart, the crude extract of Acorus calamus (Ac.Cr) at 0.01–10 mg/mL partially suppressed force of ventricular contractions (FVC), heart rate (HR) and coronary flow (CF). The ethylacetate fraction completely suppressed FVC, partially suppressed HR and CF, while the nHexane fraction exhibited similar effect on FVC and HR but increased CF, similar to methacholine and arachidonic acid. In bovine coronary arterial preparations, Ac.Cr caused inhibition of U46619 (20 nM)-precontractions, which was blocked in presence of increasing concentration of K⁺ (4.8–20 mM), tetraethylammonium (1 μM) and SKF525A (10 μM), similar to arachidonic acid and methacholine, indicating K⁺ channels activation and possible involvement of endothelial-derived hyperpolarizing factor (EDHF). Activity-directed fractionation revealed that EDHF-mediated activity is concentrated in the nHexane fraction. When tested against high K⁺, the ethylacetate fraction was found more potent than parent crude extract and nHexane fraction. These data indicate that Ac.Cr mediates coronary vasodilator effect primarily through EDHF, responsible for the increase in CF, while the cardiac depressant effects may be due to the presence of additional cardiac depressant constituent(s), thus provides possible mechanistic basis to its medicinal use in ischemic heart diseases.