Antispasmodic, bronchodilator and blood pressure lowering properties of Hypericum oblongifolium--possible mechanism of action.

The crude extract of Hypericum oblongifolium (Ho.Cr), which tested positive for flavonoids, saponins and tannins caused concentration-dependent (0.1-1.0 mg/mL) relaxation of spontaneous and high K(+) (80 mM)-induced contractions in isolated rabbit jejunum preparations, suggesting a Ca(++) antagonistic effect, which was confirmed when pretreatment of the tissue with Ho.Cr produced a rightward shift in the Ca(++) concentration-response curves, like that caused by verapamil. Ho.Cr relaxed carbachol (1 microM) and high K(+)-induced contractions in guinea pig tracheal preparations. It caused a dose-dependent (3-100 mg/kg) fall in arterial blood pressure of rats under anesthesia. In isolated guinea pig atria, Ho.Cr caused inhibition of both atrial force and rate of spontaneous contractions. When tested in rabbit aortic rings, Ho.Cr exhibited a vasodilator effect against phenylephrine (1 microM) and high K(+)-induced contractions. These results indicate that Ho.Cr possesses gastrointestinal, respiratory and cardiovascular inhibitory effects, mediated via a Ca(++) antagonist mechanism.