Tumor necrosis factor alpha system in the bovine oviduct: A possible mechanism for embryo transport

Active contractile pattern of the oviduct occurs during the periovulatory period for the movement of the gamete/embryo, which is strictly regulated by endocrine and paracrine/autocrine factors. In this review, an involvement of tumor necrosis factor a (TNFa) in the regulation of cow oviductal contraction is discussed. Oviductal epithelial cells express TNFa ligand and it's both receptor types; high expression during the follicular and postovulatory stages, while low exptession during luteal stage and thus, TNFa system in the cow oviduct is most active during the periovularoty period. The immune cells present in large numbers in the oviduct during the periovulatory period of the estrus cycle, and these cells are also considered as another potential source for the TNFa in the oviduct. Using in vitro models, TNFa clearly stimulated local production and release of contraction related substances such as prostaglandins (PGs), endothelin-1 (ET-1) and angiotensin 2 (Ang 2). Since these substances have been shown to activate directly the oviductal contraction in vitro. TNFa appears to stimulate the oviductal contraction during the periovulatory period and contribute to create an optimal local environment suitable for gamete/embryo transport. In addition, the ability of embryo to act as a source of TNFa in the oviduct cannot be excluded. To support this idea, the embryo at 2-4 cells stages indeed express TNFa, so that the minute quantities of TNFa secreted by the embryo may further acts locally to enhance the production of PG, ET-1 and Ang 2 in the oviduct, which may result in an active oviductal contraction in the microenvironment around the embryo. This may ensure the embryo to migrate into the uterus at the optimal time.