Expression of vascular endothelial growth factor (VEGF) and its receptors during embryonic implantation in the golden hamster (Mesocricetus auratus)

Expression of vascular endothelial growth factor/vascular permeability fact or (VEGF/VPF) and its receptors (flt-1 and flk-1) during the peri-implantat ion period (days 3, 4, 5, 6 and 7 post coitus) in the golden hamster was in vestigated by in situ hybridization, immunohistochemistry and the reverse t ranscription/polymerase chain reaction (RT-PCR). Three days after mating, i n situ hybridization and immunohistochemical staining revealed weak VEGF ex pression only in the uterine epithelium; this expression was similar to tha t seen at oestrus. Flt-1 but no flk-1 immunoreactivity was observed. At day 4, the subepithelial stroma and embryo displayed immunoreactivity for VEGF and flt-1, whereas endothelial cells expressed both flt-1 and flk-1. At da y 5, immunoreactivity for both VEGF and its receptors was detected in decid ual cells and vascular endothelial cells. Only a few embryonic cells expres sed VEGF mRNA but strong signals were noted in decidual cells. The patterns of VEGF and VEGF receptor expression were the same in the day-6 and day-7 embryos and decidua, except for an increase in intensity as development pro gressed Based on these findings, we conclude that, in addition to its known actions on endometrial angiogenesis and tissue swelling, VEGF may also fac ilitate the proliferation and differentiation of the endometrium and help t o sustain the avascular embryo during this early stage of development.