Implantation is a complex process that requires both synchrony in development and communication between maternal uterine cells and the blastocyst. The ovarian steroid hormones estrogen and progesterone prime the uterus for implantation. In mice, a secondary surge of estrogen on gestational Day 4 triggers the induction of implantation and the production of growth factors in the uterus. These growth factors are thought to work in an autocrine/paracrine fashion to mediate the effects of estrogen in the uterus (see for review) and therefore have been termed “es-tromedins”.
Evidence suggests that the insulin-like growth factors (IGFs) are involved in estrogen-induced uterine proliferation (see for review). IGF-I and the IGF-I receptor (IGF-IR) are expressed in the uterus, and estrogen up-regulates the expression of both genes. In vitro, IGF-I acts synergistically with estrogen to induce DNA synthesis in uterine tissue. These studies suggest that IGF-I may be an estromedin during the process of implantation. buy asthma inhalers
The IGF binding proteins (IGFBPs), another component of the IGF signaling pathway, have been shown to be important modulators of IGF action, both in vivo and in vitro, in a variety of systems. Thus far, seven IGFBPs have been cloned and sequenced, all of which have been shown to specifically bind the IGFs (see for review).