Andrographis paniculata (Ness) induces relaxation of uterus by blocking voltage operated calcium channels and inhibits Ca⁺² influx

The possible relaxation of uterine smooth muscle by Andrographis paniculata dried extract via a blockade of voltage operated calcium channels was investigated in rats. Uterine horns pretreated with oestradiol were incubated in Ca⁺²-free Jalon's solution and stimulated with KCl (20–60 mM) in order to produce depolarization of the membrane. The isometric contractile response to 1 mM or cumulative concentrations of CaCl₂ were blockaded by 0.2, 0.4 and 0.8 mg/mL of A. paniculata. The maximum contractile response induced by acetylcholine was moderately antagonized by A. paniculata. The possible blockade of Ca⁺² entry by A. paniculata was evaluated with ⁴⁵Ca⁺² uptake in uterine rings incubated with free-Ca⁺²-Ringer's solution high in K⁺ (KCl 40 mM). The influx was completely blockaded with 0.4 mg/mL of A. paniculata. These results strongly suggest that A. paniculata blockades voltage operated calcium channels inhibiting the entry of Ca⁺² from the external medium. Copyright © 2001 John Wiley & Sons, Ltd.