Puerarin, a selective oestrogen receptor modulator, disrupts pregnancy in rats at pre-implantation stage

The tubers of Pueraria tuberosa have folkloric repute as emmenagogue. The n-BuOH fraction of the ethanolic extract of tubers exhibits significant antifertility activity in laboratory animals. The present investigation explored the active principle(s) of the tuber extract with reference to contragestive effects in rats and probed the possible mechanism of action. Bioactivity-guided fractionation identified puerarin as the major constituent that exerted pregnancy-terminating effects. Oral administration of puerarin at ≥300  mg/kg per day for days (D) 1-2 post-coitus resulted in complete implantation failure. Serum oestradiol levels during D2-D5 and progesterone (P(4)) level on D5 remained unaffected, but the endometrial expression of oestrogen receptor α (ERα) and ERβ was adversely modulated that disrupted the implantation-specific characteristic endometrial oestrogenic milieu. The eventual consequence was loss of endometrial receptivity characterised by down-regulation of the uterine expression of P(4) receptor (PR) and attenuation of endometrial expression of leukaemia inhibitory factor, vascular endothelial growth factor and cyclo-oxygenase-2, the three important signalling molecules involved in the process of implantation. Light microscopic examination of the embryos demonstrated no untoward effect of puerarin on the development of embryos until D4, but D5 blastocysts underwent gross morphological distortion. The findings taken together are interpreted to suggest that puerarin adversely impacts the uterine expression of ER and PR that disrupts the implantation-conducive uterine milieu and prevents implantation. In conclusion, puerarin may be envisaged as a prospective molecule that merits further exploration for the development of non-steroidal post-coital contraceptive for women.