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  • Title: Zoapatle. XII. In vitro effect of kaurenoic acid isolated from Montanoa frutescens and two derivatives upon human spermatozoa.
    Author: Valencia A, Wens A, Ponce-Monter H, Pedrón N, Gallegos AJ, Quijano L, Calderón J, Gómez F, Ríos T.
    Journal: J Ethnopharmacol; 1986 Oct; 18(1):89-94. PubMed ID: 3821137.
    Abstract:
    Zoapatle aqueous crude extract (ZACE) from Montanoa tomentosa has been used as an oral contraceptive in traditional Mexican medicine for centuries. Kaurenoic acid, as isolated from Montanoa frutescens, and the methyl esters of 15-hydroxy-dihydro-kaurenoic acid and 15-keto-dihydro-kaurenoic acid were tested in vitro on human sperm motility and viability. The estimated ED50 concentrations immobilization were 374, 126 and 58 micrograms/ml, respectively using 15 X 10(6) sperms/500 microliter. Kaurenoic acid and both of its derivatives displayed only weak to negligible capacity for killing human sperms. The effects on human sperm motility and viability of 3 compounds isolated from an aqueous extract of Montanoa frutescens Cerv (Compositae, Heliantheae) were tested. The plant is related to the zoapatle, traditionally used as a contraceptive, and known to have uterotonic and luteolytic activity. Kaurenoic acid, its 15 hydroxy- and its methyl ester were prepared from the polar fraction, and dissolved in 95% ethanol at a concentration of 10 mg/ml. Human sperm, suspended in Bigger's Whitten and Wittingham medium at a final concentration of 15 million sperm per 500 mcl were incubated at 37 degrees C. for 60 seconds. Judging sperm motility under phase contrast microscopy, kaurenoic acid was 0.89 times less effective, and the hydroxy kaurenoic acid 2.6 times more effective than verapamil, while the keto derivative was 5.7 times more potent than verapamil at the same concentration. Sperm viability assessed by vital staining was hampered only about 10% by the keto-kaurenoic acid, 21% by kaurenoic acid, and 33% by hydroxy-kaurenoic acid. Doses required for immobilization of 50% of human sperms ranged from 58 to 374 mcg/ml. This is 225 times lower than that reported for gossypol in vitro, and much lower than the millimolar range needed to inactivate sperm with nonoxynol. Thus these drugs may prompt a search for analogs useful in vaginal contraceptives.
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