Gene Expression Changes in the Ovary Mediate Non-Anovulatory Mechanisms of Contraception with Levonorgestrel

Abstract

Emergency contraception with levonorgestrel (LNG) is a viable option to prevent unintended pregnancies. Although the efficacy of LNG as an anovulatory agent decreases as treatment approaches ovulation, it still provides some contraceptive benefits. To better understand the contraceptive mechanisms of LNG in ovulatory subjects. We conducted a study on Wistar rats that received a single dose of LNG (0.01 or 0.05 mg/kg) on the morning of proestrus before ovulation and evaluated its effects on ovarian gene expression, ovulation, and implantation. Our findings showed changes in the expression of genes involved in follicular development and oocyte quality. Pregnancy rates - as an indicator of ovulation - and embryo implantation were significantly lower than those in the control group. This study suggests that LNG alters regulatory factors in the ovary that are essential for the development of competent fertilizable oocytes, highlighting the non-anovulatory mechanisms by which levonorgestrel may regulate fertility and suggesting that it could be a novel observation that contributes to the understanding of emergency contraception in humans.