Endocrine disruption of uterine insulin-like growth factor expression in the pregnant gilt

Early exposure of pregnant gilts to oestrogen, prior to the normal period of porcine conceptus oestrogen secretion, disrupts the uterine environment resulting in complete embryonic mortality during the period of placental attachment to the uterine surface. The current study evaluates the uterine insulin-like growth factor (IGF) system following endocrine disruption of early pregnancy in gilts through exposure to exogenous oestrogen on Days 9 and 10 of gestation. Endometrial IGF gene and protein expression, IGF-I receptor (IGF-IR) gene expression, and uterine lumenal content of IGF binding proteins (IGFBPs) were evaluated in control and oestrogen-treated gilts on Days 10, 12, 13, 15 and 17 of gestation. Oestrogen treatment altered endometrial IGF-I and IGF-IR gene expression on Days 12 and 13 of gestation. Uterine content of IGF-I and IGF-II in control gilts was greatest on Days 10, 12, and 13 followed by a four- to sixfold decrease on Day 15 of gestation. Oestrogen treatment caused a premature proteolysis of IGFBPs within the pregnant pig uterus on Day 10 of gestation, and an earlier decline in uterine lumenal IGF-I content. Results demonstrate that early exposure of pregnant gilts to oestrogen causes premature loss of uterine IGFs during the period of conceptus elongation. Timing for the release of uterine IGFs during early porcine conceptus development may play an important function in the ability of the conceptus to attach and survive during the establishment of pregnancy.