Beschreibung:
<jats:title>Summary</jats:title><jats:p>Levonorgestrel, a derivative of progesterone, effectively protects women against unwanted pregnancy as an emergency contraceptive. Previous studies have not been successful in determining the mechanism by which levonorgestrel acts. In the present study we analysed cilia beat action and cilia morphology following levonorgestrel exposure <jats:italic>in vitro</jats:italic> and <jats:italic>in vivo</jats:italic> using both light and electron microscopy. There was a significant decrease in the ciliary beat frequency (<jats:styled-content style="fixed-case">CBF</jats:styled-content>) of human fallopian tubes between mucosal explants bathed in 5 <jats:italic>μ</jats:italic>mol/L levonorgestrel and those bathed in medium alone (<jats:italic>P </jats:italic>< 0.05). There was a tendency for <jats:styled-content style="fixed-case">CBF</jats:styled-content> to decrease more in the ampulla than in isthmus, but there were no differences between the proliferative and secretory phases. In rat oviducts, levonorgestrel produced a similar reduction in <jats:styled-content style="fixed-case">CBF</jats:styled-content> (~ 10%) compared with the saline control group (<jats:italic>P </jats:italic>< 0.05). Histological and ultrastructural analysis demonstrated no changes in the percentage of ciliated cells or in the classic ‘9 + 2’ structure of cilia following levonorgestrel treatment in either system. Thus, levonorgestrel reduces <jats:styled-content style="fixed-case">CBF</jats:styled-content> without damaging cilia morphology. Decreases in <jats:styled-content style="fixed-case">CBF</jats:styled-content> may indicate a pathological role for levonorgestrel in the transportation of the ovum and zygote in the fallopian tube.</jats:p>