The expression of IGF-I and IGFBP-4 mRNA in the periimplantation mouse uterus correlates both temporally and anatomically to many of the events of implantation. In the current study, we demonstrate that decidualization of the uterine stroma, in the absence of an embryo, can maintain IGF-I and IGFBP-4 mRNA expression beyond gestational Day 4. As decidualization of the uterine stroma progressed, IGF-I mRNA expression was confined to the non-decidualized, outer stroma and myometrial layer. In contrast, intense IGFBP-4 mRNA signal was detected in decidualized endometrial stroma. An earlier study conducted in rat deciduomata tissue demonstrated similar results for IGF-I expression but very different results for another inhibitory binding protein, IGFBP-1. Unlike IGFBP-4, IGFBP-1 mRNA was detected only in uterine epithelial cells and in the stromal glands in the antimesometrial area. Differences in cellular distribution of IGFBP-1 and IGFBP-4 mRNA suggest different actions for these two potential IGF-I inhibitors in the decidual reaction. flovent inhaler
Evidence suggests that IGF-I may play a role in uterine cell proliferation and/or differentiation. Specifically, IGF-I was able to synergize with estrogen to induce DNA synthesis, predominantly in the outer half of the uterine stroma; and in vitro, IGF-I has been shown to regulate the secretion of two specific products of human decidualized endometrial cells, prolactin and IGFBP-1. IGF-I has also been shown to stimulate DNA synthesis in primary cultures of endometrial stromal cells isolated from Day 12 pig endometrium, a period in which IGF-I mRNA is expressed at high levels in vivo. In addition, IGF-I null mutant female mice possess infantile uteri that exhibit extreme hypoplasia, particularly in the myometrium.