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-polyme rase chain reaction (RT-PCR) and ribonuclease protection assay (RPA) were u sed to show that the bovine oviduct expresses VEGF and its two receptors fl k-1 and flt-1. Expression of VEGF was relatively stable during the estrous cycle. In contrast, both receptor transcripts showed cycle-dependent variat ions with significantly increased flt-1 mRNA amounts before ovulation. Immu nohistochemical studies localized VEGF mainly on the epithelial surface of oviducts. Protein concentrations of VEGF in oviductal flushings were signif icantly higher (mean +/- SEM: 2.8 +/- 0.8 ng/ml) during the pre-ovulatory p hase 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 ovi duct were found to undergo specific modulations during the cycle. We sugges t that VEGF may be involved in creating an optimal local environment for fe rtilization or the developing embryo by modulating permeability within the bovine oviduct. (C) 1999 Wiley-Liss, Inc.