Abstract
The normal intrauterine fluid environment is essential for embryo implantation. In hydrosalpinx patients, the implantation and pregnancy rates are markedly decreased after IVF–embryo transfer, while salpingectomy could significantly improve the pregnancy rates. The leakage of hydrosalpinx fluid into the endometrial cavity was supposed to be the major cause for impaired fertility. However, the underlying mechanisms of hydrosalpinx fluids on implantation and ongoing pregnancy were not fully understood and remain controversial regarding its toxicity. In present study, by infusing different volume of non-toxic fluid (0.9% saline) into uterine lumen before embryo implantation in mice (Day4 08:30), we found that while the embryos were not “flushed out” from the uteri, the timing of implantation was deferred and normal intrauterine distribution (embryo spacing) was disrupted. The abnormal implantation at early pregnancy further lead to embryo growth retardation, miscarriage and increased pregnancy loss, which is similar to the adverse effects observed in hydrosalpinx patients undergoing IVF-ET. We further examined uterine receptivity related gene expression reported to be involved in human hydrosalpinx (Lif, Hoxa10, Integrin α(v) and β(3)). The results showed that expression of integrin α(v) and β(3) were increased in the fluid infused mouse uteri, implicating a compensatory effect to cope with the excessive fluid environment. Our data suggested that the adverse effects of excessive non-toxic luminal fluid on pregnancy are primarily due to the mechanical interference for normal timing and location of embryo apposition, which might be the major cause of decreased implantation rate in IVF-ET patients with hydrosalpinx.
Highlights
The mammalian embryo implantation happens in a receptive endometrium with well-regulated fluid environments [1]
To examine the hypothesis that whether the previously supposed toxic components of hydrosalpinx fluid is necessary to cause adverse embryo implantation, here we firstly used the sterilized saline for intrauterine infusion at preimplantation uteri, and examined the implantation rate at Day6 by blue dye reaction
The 0 μl group means that the mice were under the same surgical procedure but only with an empty needle pricking into the uterine lumen without fluid infusion. These data clearly demonstrated that excessive intrauterine fluid, even by the non-toxic sterilized saline, could significantly decrease implantation rate, indicating that the inflammatory factors in fluid is not necessary for the adverse effects
Summary
The mammalian embryo implantation happens in a receptive endometrium with well-regulated fluid environments [1]. Before the embryo(s) attached to the uterine wall, on-time reabsorption of intra-luminal uterine fluid is supposed to be necessary for uterine luminal closure, which facilitates the interactions between the embryo and the epithelial lining to initiate attachment reaction [1,2]. This assumption was supported by the observation that uterine luminal fluid reabsorption peaks at the expected time of implantation in rodents [3,4], which is controlled by concerted ovarian hormone secretions and local ion and water channels [1,3,4,5,6]. The leakage of hydrosalpinx fluid into the endometrial cavity was supposed to be the major cause for the low IVF success rate [10,11,12]. This idea has been substantiated by the facts that treatments such as salpingectomy/occlusion of proximal tube, which prevent the leakage of hydrosalpinx fluid, could significantly improve the success of IVF-ET in treated patients [13,14,15,16]
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