A chronic low dose infusion of insulin-like growth factor I alters placental function but does not affect fetal growth

Abstract

Knowledge of the anabolic effects of insulin-like growth factor I (IGF-I) on fetal growth and feto–placental metabolism are derived from studies using large doses of IGF-I. Low doses of enteral IGF-I have trophic effects on the fetal gut, but there are no data on the effects of systemic low doses of IGF-I on fetal growth and feto–placental metabolism. We therefore compared the effects of a chronic infusion of low dose IGF-I (50 μg day^–1, n = 7) with vehicle-infused controls (n = 7) on fetal growth, metabolism and placental transfer capacity in the chronically instrumented late gestation ovine fetus (121–132 days of gestation; term = 145 days). Insulin-like growth factor I infusion did not affect fetal growth or the size of individual organs, including liver, spleen and bone. Placental morphology was altered, and placental clearances of 3-O-[methyl-³H]D-glucose (a non-metabolizable glucose analogue) and [methyl¹⁴C]aminoisobutyric acid (a non-metabolizable analogue of amino acids utilizing the system A transporter), were reduced in IGF-I-treated fetuses (P<0.05 v. control). However, fetal and placental metabolite uptake was not significantly different between groups. We conclude that, despite altering placental transfer capacity and morphology, a chronic low dose infusion of IGF-I does not alter fetal growth or metabolism.