Effects of oblongine chloride,an alkaloid from Leontice leontopetalum on guinea-pig isolated smooth muscle and heart

1. The effects of (−)oblongine chloride, a quaternary alkaloid from Leontice leontopetalum, on guinea-pig isolated ileal longitudinal segments, main pulmonary artery rings, spontaneously-beating atrium and isolated perfused heart were studied.2. Oblongine chloride (3 × 10⁻⁵−10⁻³ M) caused concentration-dependent relaxation of ileum, an effect which was not blocked by propranolol (10⁻⁶ M) alone or in combination with prazosin (3 × 10⁻⁸ M), or by indomethacin (10⁻⁶ M), but was reduced by desensitization of the preparation by prior exposure to 3 × 10⁻⁵ M ATP and, at high concentrations of oblongine, by a combination of propranolol and yohimbine (3 × 10⁻⁶ M).3. Oblongine chloride (10⁻⁵−3 × 10⁻³ M) caused concentration-dependent relaxation of epinephrine-precontracted pulmonary artery. This effect was not affected by propranolol or by indomethacin but was significantly attenuated by pretreatment with 3 × 10⁻⁵ M ATP and potentiated by pretreatment with quinacrine (10⁻⁵ M).4. Oblongine chloride (10⁻⁵M−3 × 10⁻³ M) caused concentration-dependent increase in the contractility but did not affect the rate of the atrium. Similar effects were obtained with isolated perfused heart except that large concentrations of oblongine (10⁻³, 3 × 10⁻³ M) inhibited both contractility and rate of the heart. The inotropic effects of oblongine on the atrium were not blocked by propranolol or indomethacin but were significantly blocked by quinacrine.5. These observations suggest that the effects of oblongine chloride are not mediated by the stimulation of adrenergic receptors on these preparations but are mediated by purinergic receptors and by an interference with the arachidonic acid metabolism but not along the cyclooxygenase pathway.