Effect of 14‐deoxyandrographolide on calcium‐mediated rat uterine smooth muscle contractility

In this study, the effect of 14‐deoxyandrographolide (14‐DAP) on calcium channel‐dependent rat uterine smooth muscle contraction was evaluated. Using a tissue bath preparation, 14‐DAP was able to reduce the contractile response to 0.3 and 3.0 mm of CaCl 2 , with an IC 50 of 1.24 ± 0.23 × 10 −5 m and 5.94 ± 0.29 × 10 −5 m , respectively. 14‐DAP shifted the CaCl 2 cumulative dose response curve to the right, increasing the EC 50 from 2.08 ± 0.20 × 10 −4 m to 4.22 ± 0.22 × 10 −4 m (5 µ m 14‐DAP) and 2.5 ± 1.0 × 10 −3 m (50 µ m 14‐DAP). In order to determine if 14‐DAP had any effect on intracellular calcium, the relaxant response to 14‐DAP following contraction by oxytocin, PGF 2 α and vanadate in Ca +2 ‐free solution was compared with that of isoproterenol and phenylbutazone. While isoproterenol and phenylbutazone relaxed the smooth muscle in a dose‐dependent manner, 14‐DAP did not have any effect on either the oxytocin, PGF 2 α or vanadate‐induced smooth muscle contraction. Based on these data, it appears that 14‐DAP is an uterine smooth muscle relaxant which produces a selective blockade of voltage operated calcium channels. Copyright © 2003 John Wiley & Sons, Ltd.