Formation of Fallopian tubal fluid: role of a neglected epithelium

Abstract

In mammals, fertilization and early embryo development occur in the oviduct (Fallopian tube). The oviduct also acts as a sperm reservoir after mating. Anyone unfamiliar with this information might imagine that the formation of oviductal fluid, the medium in which these processes occur, had been studied extensively. They would be wrong. Compared with the wealth of data on other epithelial tissues, for example, those lining the gastrointestinal tract, kidney tubules and airways, there is a paucity of information on the formation of oviductal fluid. A major reason for the lack of investigation is the success of in vitro fertilization (IVF) and embryo transfer (ET) techniques, in which the oviduct is bypassed, creating the impression that the study of oviductal fluid is somewhat redundant. However, this is akin to saying that there is no need to study the intestine, kidney or airways since people can be kept alive parenterally, by kidney dialysis or by artificial respiration, respectively. Undoubtedly, there is a practical need to improve IVF success rates, ensure the normality of the embryos created and increase knowledge about the first environment to which embryos are exposed. Because the mechanisms underlying oviductal fluid formation have yet to be elucidated in any detail, the hormonal and nervous control of the processes involved are not fully understood, nor are the possible pharmacological effects, which might have a clinical role. By the same token, the mechanisms that integrate the actions of the myosalpinx (the muscle component of the oviduct) and the endosalpinx (the mucosal lining) have yet to be explored. This review considers: (i) key features of the composition of oviductal fluids; (ii) the few studies that have addressed the mechanisms that underlie oviductal fluid secretion; (iii) the effect of modulators of oviductal fluid secretion and their functional significance; and (iv) clinical implications of research on oviductal secretion.