TRPV4 is involved in levonorgestrel-induced reduction in oviduct ciliary beating

Previous studies revealed the increasing risk of tubal pregnancy following failure of levonorgestrel (LNG)-induced emergency contraception, which was attributed to the reduced ciliary motility in response to LNG. However, understanding of the mechanism of LNG-induced reduction in the ciliary beat frequency (CBF) is limited. The transient receptor potential vanilloid (TRPV) 4 channel is located widely in the female reproductive tract and generates an influx of Ca²⁺ following its activation under normal physiological conditions, which regulates the CBF. The present study aimed to explore whether LNG reduced the CBF in the Fallopian tubes by modulating TRPV4 channels, leading to embryo retention in the Fallopian tubes and subsequent tubal pregnancy. The study provided evidence that the expression of TRPV4 was downregulated in the Fallopian tubes among patients with tubal pregnancy and negatively correlated with the serum level of progesterone. LNG downregulated the expression of TRPV4, limiting the calcium influx to reduce the CBF in mouse oviducts. Furthermore, the distribution of ciliated cells and the morphology of cilia did not change following the administration of LNG. LNG-induced reduction in the CBF and embryo retention in the Fallopian tubes and in mouse oviducts were partially reversed by the progesterone receptor antagonist RU486 or the TRPV4 agonist 4α-phorbol 12,13-didecanoate (4α-PDD). The results indicated that LNG could downregulate the expression of TRPV4 to reduce the CBF in both humans and mice, suggesting the possible mechanism of tubal pregnancy. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.