Placental barrier to human insulin-I125 in insulin-dependent diabetic mothers.

Abstract

Although the normal human placenta is impermeable to insulin, the effect of anti-insulin antibodies on this placental barrier in insulin-dependent diabetic mothers is not known. The placental transfer of human insulin-I125 was examined in 4 normal and 4 insulin-dependent diabetic mothers. Human insulin-I125 was infused at a constant rate for 60–90 min prior to delivery and immuno-precipitable insulin-I125 was measured in the maternal and umbilical venous plasma at delivery. In diabetic patients, insulin-I125 was separated from circulating endogenous anti-insulin antibodiesby acid alcohol extraction prior to immunoprecipita-tion. In normal mothers insulin-I125 radioactivitywas 683 ±110 cpm/ml (mean ± sem) in the maternal vein and 6 ± 2 cpm/ml in the umbilical vein. In three diabetic mothers with high plasma insulin binding capacities between 2580–8400 μU/ml, the umbilical venous insulin-I125 was 10 ± 10 cpm/ml when the maternal plasma insulin-I125 was maintained at 1388 ± 356 cpm/ml even though the antibodies were present in the fetal plasma. In another diabetic subject with low anti-insulin anti-bodies, no placental transfer of insulin-I125 was demonstrated. Thus in both normal and diabetic subjects, placental transfer of insulin-I125 is negligible and the presence of anti-insulin antibodies does not induce insulin transfer.