Immunohistochemistry for vascular endothelial growth factor (VEGF) and its receptors, fms-like tyrosine kinase (flt-1) and kinase insert domain-containing region (KDR), was performed on human endometrium obtained from patients with normal menstrual cycles, patients given oestrogen and progesterone, and women in early pregnancy. Intense immunostaining of VEGF was observed in both glandular epithelial and stromal cells during the mid-secretory phase; the immunostaining intensity was increased by administration of oestrogen plus progesterone and strong immunostaining was observed in decidual cells of early pregnancy. In addition to the immunostaining in vascular endothelial cells, strong KDR immunostaining was observed in glandular epithelial cells and in decidualized stromal cells induced by administration of oestrogen plus progesterone, whereas flt-1 immunostaining was negligible. Strong immunostaining for flt-1 and KDR was found in both vascular endothelial cells and decidual cells in early pregnancy. Endometrial stromal cells isolated from proliferative phase endometrium were incubated with oestrogen (10(-8) mol l-1) and medroxyprogesterone acetate (MPA; 10(-6) mol l-1) for 18 days to study the regulation of VEGF, flt-1 and KDR in endometrial stromal cells by oestrogen and progesterone. Expression of VEGF and KDR mRNAs was increased significantly by oestrogen and MPA, accompanied by decidualization, whereas flt-1 mRNA expression was not affected. In conclusion, VEGF and its receptors may play important roles in implantation and maintenance of pregnancy.
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