Expression of the vascular endothelial growth factor system (VEGF) in the porcine oviduct during the estrous cycle

- The overall expressions of VEGFA and KDR were higher in ampulla than in isthmus, while the opposite was found for Flt-1.
- VEFGA protein was also higher in ampulla, but Flt-1 and KDR did not changed between ampulla and isthmus.
- VEGFA expression was almost constant along the estrous cycle, but Flt-1 and KDR increased during the luteal phases. Contrastingly, VEGFA and Flt-1 proteins decreased in the luteal period (isthmus), whereas KDR protein was maximized just before ovulation (ampulla & isthmus).
- VEGFA, Flt-1 and KDR were detected in the endo and myosalpinx, but the highest concentration was found in the epithelium of both ampulla and isthmus.
- Changes in mRNA and protein levels of the VEGF system in the porcine oviduct are likely related with a regulation of the secretion of oviductal fluid and the oviduct contractibility.

The expression and localization of VEGFA and its main receptors Flt-1 and KDR is characterized in the oviduct throughout the porcine estrous cycle. Oviducts were sampled from sows at early follicular, late follicular, early luteal and late luteal stages of the estrous cycle and a segment from the mid portion of the ampulla and isthmus studied by real time RT-PCR and quantitative immunohistochemistry. The expression of the three components of the VEGF system was continuous, although differences were observed depending on the oviduct portion, the stage of the estrous cycle and the histological layer. VEGFA and KDR mRNA expressions were higher in ampulla, while Flt-1 mRNA was higher in isthmus. VEGFA protein was also higher in ampulla but Flt-1 and KDR did not show regional differences between ampulla and isthmus. While the mRNA expression of VEGFA, Flt-1 and KDR increased progressively during the luteal period, the amount of VEGFA and Flt-1 protein decreased in the same period (in isthmus only). Contrastinly, KDR protein peaked in ampulla and isthmus just before ovulation. The VEGF system was majorly located in both the secretory and ciliated cells of the oviduct epithelium, but also in the endothelium and fibroblasts of the lamina propia and the muscle fibres and vessels of the tunica muscularis. Our results are consistent with a participation of VEFG in the regulation of the dynamics of oviductal fluid secretion and the oviduct contractibility.