Antifertility activity of Montanoa tomentosa (Zoapatle).

According to folklore medicine, the Mexican plant zoapatle (Montanoa tomentosa) possesses antifertility activity in women. We report here the effect of various isolated preparations from this plant on early pregnancy in several rodent species including the mouse, rat, hamster, and guinea pig. When an aqueous extract of the leaves similar to the tea utilized in folklore medicine was administered orally during early stages of pregnancy, no antifertility activity could be detected. Day 22 pregnant guinea pigs, however, provided an animal model which allowed conservation of test materials and which showed the antifertilty activity of the plant extracts. Purer fractions derived from the plant were more potent in this assay system when administered either intraperitoneally or orally. As the purity of the extracts (and hence the quantity of active ingredient administered) increased, we were able to demonstrate inhibition of implantation in rats and mice when administered on days 1-6 and in hamsters when administered on days 4-6 of gestation. Preliminary data indicate the plant extracts are not estrogenic. It is concluded that zoapatle plant extracts possess unique antifertility activity.