During pregnancy, the decidua is comprised of two separate tissues located either mesometrially or antimesometrially in the uterus. Trophoblast invasion takes place only in the mesometrial decidua, where extensive angiogenesis, essential for successful implantation, occurs. Both basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) have been implicated in this phenomenon. The aim of this study was to determine whether the expression of both growth factors is intrinsic to decidua and occurs in the absence of conceptuses, whether their genes are expressed specifically in the mesometrial decidua, the site of angiogenesis, and whether both growth factors are developmentally and hormonally regulated. Decidual tissue was dissected from pseudopregnant rats and levels of both bFGF and VEGF mRNA were examined in mesometrial and antimesometrial decidua by semi-quantitative RT-PCR at different stages of pseudopregnancy. Although induction of decidualization triggered the mRNA expression of bFGF, VEGF mRNA expression remained unchanged. VEGF mRNA level was similar in both antimesometrial and mesometrial decidua, and remained constant throughout pseudopregnancy. In sharp contrast, bFGF mRNA was highly expressed in the mesometrial decidua at a time when extensive angiogenesis takes place in this tissue. Very little signal was observed in the antimesometrial decidua. To examine the regulation of these growth factors, we used a temperature-sensitive decidual cell line developed by transforming antimesometrial decidual cells with SV-40 tsA 209 mutant virus. These cells express both bFGF and VEGF mRNA. Because progesterone is necessary for decidualization and decidua secretes prolactin (PRL)-related hormones, we examined the role of these hormones on VEGF and bFGF mRNA expressions. Neither progesterone nor PRL had any effect on VEGF mRNA levels. However, bFGF mRNA expression was greatly stimulated by PRL. In conclusion, results of this investigation have revealed that bFGF, but not VEGF, mRNA becomes highly expressed in the mesometrial decidua, where angiogenesis occurs, and where trophoblasts, by invading decidual cells, may promote the release of bFGF. In addition, these results indicate that the locally secreted PRL-like hormone up-regulates the mRNA expression of bFGF.

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