Importance of Water Transport in Mammalian Female Reproductive Tract

SIMPLE SUMMARY: The female reproductive tract undergoes several structural changes during estrus and menstrual cycles, pregnancy and parturition that involve important regulation of the exchange of solutes to prepare the uterus for conception, implantation and fetal development. The expression of a particular aquaporin isoform has specific locations in the reproductive tract that differs among species probably because of the type of uterine anatomy or type of placentation. These locations involve different actions, metabolism and functions. AQPs have been identified, but the regulation of water transportation in the uterus and placenta is poorly understood. The expression and location of aquaporins in the uterus are regulated by ovarian steroid hormones such as estradiol and progesterone, suggesting that these aquaporins play important roles in water and other solutes transportation in uterine imbibition and amniotic fluid resorption. ABSTRACT: Aquaporins (AQPs) are involved in water homeostasis in tissues and are ubiquitous in the reproductive tract. AQPs are classified into classical aquaporins (AQP0, 1, 2, 4, 5, 6 and 8), aquaglycerolporins (AQP3, 7, 9, and 10) and superaquaporins (AQP11 and 12). Nine AQPs were described in the mammalian female reproductive tract. Some of their functions are influenced by sexual steroid hormones. The continuous physiological changes that occur throughout the sexual cycle, pregnancy and parturition, modify the expression of AQPs, thus creating at every moment the required water homeostasis. AQPs in the ovary regulate follicular development and ovulation. In the vagina and the cervix, AQPs are involved mainly in lubrication. In the uterus, AQPs are mostly mediated by estradiol and progesterone to prepare the endometrium for possible embryo implantation and fetal development. In the placenta, AQPs are responsible for the fluid support to the fetus to maintain fetal homeostasis that ensures correct fetal development as pregnancy goes on. This review is focused on understanding the role of AQPs in the mammalian female reproductive tract during the sexual cycle of pregnancy and parturition.