Expression of mRNA for vascular endothelial growth factor transmembraneousreceptors Flt1 and KDR, and the soluble receptor sflt in cycling human endometrium

The aim of this study was to quantify and localize the mRNA expression of t he vascular endothelial growth factor (VEGF) receptors Flt1, KDR and sflt, in human endometrium throughout the menstrual cycle. Since neoangiogenesis is crucial during embryonic implantation, we postulate that endometrial rec eptivity to VEGF may be altered during the luteal phase in order to support implantation. Human endometrium was collected and specified as early proli ferative (n = 3), mid-proliferative (n = 4), late proliferative (n = 3), ea rly secretory (n = 2), mid-secretory (n = 4), and late secretory (n = 4). C ompetitive reverse transcription-polymerase chain reaction (RT-PCR) was per formed to evaluate the mRNA values throughout the menstrual cycle. Addition ally, four samples were separated into epithelial and stromal-enriched cell fractions and competitive RT-PCR was carried out to specify the distributi on of the mRNA expression. While mRNA for the transmembraneous receptors Fl t1 and KDR was shown to be present at almost constant values throughout the menstrual cycle, the soluble receptor, sflt, had a three-fold higher level of transcription during mid-proliferative and late proliferative when comp ared with early proliferative and the entire secretory phase. The expressio n of Flt1, KDR and sflt mRNA was detected in both isolated endometrial epit helial and stromal cell fractions. In conclusion, the down-regulation of sf lt, which functions as a soluble antagonist, during the luteal phase may ac t to sensitize the maternal endothelial receptors to angiogenetic stimuli s ecreted by the implanting embryo.