Controlled ovarian hyperstimulation (OH) is a technique used during human fertility treatments, such as in vitro fertilisation (IVF), which stimulates the growth of several follicles resulting in superovulation. However, this treatment changes the normal hormone levels, which may negatively effect embryo implantation and placental development. Vascular endothelial growth factor (VEGF) is an important protein involved in these processes, however the altered hormone profile may impact the normal expression of VEGF and its receptors.
A recently developed rat OH model is a useful technique in studying the changes in the endometrium in response to fertility drugs, similar to those used in human IVF procedures, however studies of VEGF in this model are limited.
Female rats with at least 2 continuous 4-day oestrus cycles were injected with an IP injection of 20 IU of equine serum gonadotropin followed by 20 IU of human chorionic gonadotropin 24-hours later. The rats were then mated overnight and sacrificed on days 1, 3, 6, 7 and 9 of OH and normal pregnancy. The uterine tissue was then collected and processed for immunohistochemistry and western blot analysis.
So far our results suggest that both VEGF and VEGFR2 are expressed at lower levels in OH rats compared to normal pregnant rats from as early as day 1, the time of fertilisation. This lower level of expression in OH is also maintained at day 6, the time of implantation.
Collection of tissue from later stages of pregnancy is ongoing to determine if changes in VEGF and VEGFR2 in OH influence placental development and contribute to placental anomalies.
Thus the lower levels of VEGF and VEGFR2 seen in OH compared to normal pregnancy may add to our understanding of changes in the endometrium in response to fertility drugs, and explain the observed lower uterine receptivity seen in IVF patients.