Expression of insulin-like growth factor-I and insulin-like growth factor-binding protein-1 in the rat uterus during decidualization.

Decidualization of the uterus involves proliferation and differentiation of uterine cells. The effects of decidualization on uterine expression of insulin-like growth factor-I (IGF-I) and IGF-binding protein-1 (IGFBP-1) have been examined in the hypophysectomized-ovariectomized (hypox-ovx) rat and the pituitary-intact (ovx) rat. Decidualization was induced by uterine stimulation of animals treated with a combination of 17 beta-estradiol and progesterone. The patterns of change in uterine IGF-I mRNA and IGFBP-1 mRNA abundance were similar to hypox-ovx rats, hypox-ovx rats replaced with GH and T4, and ovx rats. The changes in IGF-I mRNA abundance were temporally related to 17 beta-estradiol injections. IGFBP-1 mRNA was undetectable early in the decidualization process and reached maximal levels on day 6. Mechanical separation of the deciduoma tissue from the underlying myometrium revealed that the deciduoma tissue was depleted in IGF-I mRNA, while the majority of the IGFBP-1 was located in the deciduoma tissue. The in situ hybridization technique was used to localize IGF-I and IGFBP-1 mRNA in the decidualized uterus. The majority of the IGF-I expression was localized to the outer stroma and smooth muscle cell layer, whereas IGFBP-1 mRNA was detected in uterine epithelial cells and stromal glands. These experiments demonstrated that uterine IGF-I and IGFBP-1 expression during the process of decidualization are pituitary independent. Furthermore, our observations support the hypothesis that the expression of IGFBP-1, a protein capable of inhibiting the mitogenic activity of IGF-I, in deciduoma tissue may inhibit paracrine IGF-1 actin and allow for the differentiation of stromal tissue.