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 alpha (TNFalpha) in the regulation of cow oviductal contraction is discussed. Oviductal epithelial cells express TNFalpha ligand and it's both receptor types; high expression during the follicular and postovulatory stages, while low expression during luteal stage and thus, TNFalpha system in the cow oviduct is most active during the periovulatory 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 TNFalpha in the oviduct. Using in vitro models, TNFalpha clearly stimulated local production and release of contraction related substances such as prostaglandins (PGs), endothelin-1 (ET-1) and angiotensin II (Ang II). Since these substances have been shown to activate directly the oviductal contraction in vitro, TNFalpha 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 TNFalpha in the oviduct cannot be excluded. To support this idea, the embryo at 2-4 cells stages indeed express TNFalpha, so that the minute quantities of TNFalpha secreted by the embryo may further acts locally to enhance the production of PG, ET-1 and Ang II 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.