Expression of KiSS-1 in rat oviduct: possible involvement in prevention of ectopic implantation?

The mammalian oviduct is a crucial site for essential postovulatory events in the female reproductive system. These events are, in part, accomplished by clear-cut oviductal segmentation, which helps to provide appropriate epithelial and fluid microenvironments. Early embryonic development and the timely transport of the embryo to the uterus must be promoted, but implantation within the oviduct itself must be avoided. Indeed, the rarity of extra-uterine pregnancies in laboratory animals strongly suggests that active mechanisms operate to prevent ectopic implantation. Kisspeptins, products of the KiSS-1 gene, have been proposed as physiological regulators of uterine implantation by limiting the invasion of the trophoblast into the maternal decidua. We describe here the patterns of expression of the KiSS-1 gene and of kisspeptin immunoreactivity (IR) in the rat oviduct. KiSS-1 mRNA is readily detectable in oviduct samples from all phases of the estrous cycle, whereas kisspeptin-IR is detected in rat oviduct with a regionalized pattern of distribution, viz., strong expression in the isthmus, faint signals in the proximal ampulla, and a lack of immunostaining in the fimbriated infundibulum and interstitial portion. When positive, IR has been localized at the adluminal surface and the cytoplasmic domain of secretory cells. Of note, KiSS-1 expression (at the mRNA and protein levels) shows cycle-related changes with peak expression in proestrus/estrus and lower levels at metestrus/diestrus. This knowledge of the regional- and cycle-specific pattern of expression of KiSS-1 in rat oviduct should open up the possibility of a physiological role of kisspeptins in the prevention of ectopic (tubal) implantation.