| Abstrakt: |
The effect of kaurenoic acid, a diterpene isolated from the oleo-resin of the popular medicinal plant Copaifera langsdorffii (Leguminaceae), was analysed on rat uterine muscle responsiveness to various drugs in vitro. Cumulative concentration-response curves to acetylcholine and oxytocin were obtained before and after incubation of uterine segments with up to 160 µm of kaurenoic acid. The maximal contractile response ( Emax) evoked by these agonists was inhibited by kaurenoic acid in a concentration-related manner; at 160 µm, kaurenoic acid depressed the Emax of oxytocin and acetylcholine by 83% and 91%, respectively. The relaxation caused by kaurenoic acid on oxytocin-induced contraction was unaffected in the presence of tetraethyl ammonium, a compound that blocks the calcium activated potassium channels. It was partially reversed by glibenclamide (10-5 m), an ATP-sensitive potassium channel blocker. Also, kaurenoic acid at 160 µm concentration was found to inhibit significantly the CaCl2-evoked contractile responses in a medium of high potassium and zero calcium. Furthermore, kaurenoic acid was found to relax the sustained tonic contraction induced by acetylcholine, oxytocin, BaCl2 and KCl in a concentration-dependent way. However, KCl-induced tonic contraction was only weakly inhibited by kaurenoic acid. These data indicate that the diterpene, kaurenoic acid, exerts a uterine relaxant effect acting principally through calcium blockade and in part, by the opening of ATP-sensitive potassium channels. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR] |
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