Effect of Ethanol Exposure on Circulating Levels of Insulin-Like Growth Factor I and II, and Insulin-Like Growth Factor Binding Proteins in Fetal Rats

Maternal ethanol (ETOH) exposure is associated with impaired fetal growth. Because insulin-like growth factors (IGFs) are thought to be important in the regulation of fetal somatic growth, we examined the influence of maternal ETOH exposure on fetal growth and plasma levels of IGF-I, IGF-II, and IGF binding proteins (IGFBPs) in the rat model. Control (A) dams were fed a standard rat chow ad libitum. ETOH (E) consuming dams were fed a 36% ETOH diet, and pair-fed (P) dams were fed isocaloric amounts of a control liquid diet. All animals were killed on day 20 of gestation. Plasma concentrations of IGF-I and -II were determined by radioimmunoassay after formic acid-acetone extraction and heat inactivation of IGFBPs. Levels of IGFBPs in fetal plasma were estimated by Western ligand blotting after protein separation by SDS-PAGE and electrotransfer to nitrocellulose. Membranes were probed with [¹²⁵l]IGF-l, and IGFBPs were identified by autoradiography, quantified by scanning densitometry and results expressed relative to corresponding IGFBPs in control fetal plasma. Maternal weight gain from conception to 20 days of pregnancy was reduced for E compared to P and A dams (p < 0.05 E vs. P or A). The same pattern was reflected in fetal weight that tended to be lower in P compared with A pups, and was significantly reduced in E pups compared with both groups (p < 0.0001 E vs. P or A). Thus, fetal growth was more retarded in E animals despite equal caloric and protein intake by E and P dams. Radioimmunoassay of fetal plasma revealed that there was no difference in circulating levels of IGF-II in A (65.5 ± 8.7 ng/ml) and P (65.9 ± 9.8 ng/ml) plasma. However, levels of IGF-II were higher in E (87.1 ± 6.2 ng/ml) than in corresponding P animals. At the same time, there were no differences in IGF-I levels between any of the treatment groups. Western ligand blotting demonstrated that levels of 32–34 kDa IGFBPs were elevated in plasma of P compared with A fetal plasma, consistent with an effect of reduced maternal nutrition. In contrast, levels of32–34 kDa IGFBPs were reduced in E plasma compared with P and A (p < 0.04 and p < 0.02, respectively). These data suggest that circulating levels of IGF-II (but not IGF-I) and specific IGFBPs are altered in growth-retarded fetuses exposed to ETOH. Comparison to fetal plasma obtained from pair-fed litters demonstrate that these effects on IGF and IGFBP levels are specific to ETOH, and not simply due to maternal nutrient intake. Taken together, these observations indicate that ETOH has unique effects on fetal IGF physiology compared with previously studied models of fetal growth retardation. Alterations in the expression and levels of IGFs and IGFBPs may contribute to ETOH-induced fetal growth deficiency.