Expression of vascular endothelial growth factor (VEGF) and its corresponding receptors (flt-1 and flk-1) in the bovine oviduct.

Vascular endothelial growth factor (VEGF) functions as a potent angiogenic protein as well as in regulating permeability. Reverse transcription-polymerase chain reaction (RT-PCR) and ribonuclease protection assay (RPA) were used to show that the bovine oviduct expresses VEGF and its two receptors flk-1 and flt-1. Expression of VEGF was relatively stable during the estrous cycle. In contrast, both receptor transcripts showed cycle-dependent variations with significantly increased flt-1 mRNA amounts before ovulation. Immunohistochemical studies localized VEGF mainly on the epithelial surface of oviducts. Protein concentrations of VEGF in oviductal flushings were significantly higher (mean +/- SEM: 2.8 +/- 0.8 ng/ml) during the pre-ovulatory phase when compared with the other estrous cycle stages (1.0 +/- 0.25 ng/ml). In conclusion, all components of a functional VEGF-system in the bovine oviduct were found to undergo specific modulations during the cycle. We suggest that VEGF may be involved in creating an optimal local environment for fertilization or the developing embryo by modulating permeability within the bovine oviduct.