THE PLACENTAL BARRIER TO HUMAN INSULIN-I-125 IN INSULIN DEPENDENT DIABETIC MOTHERS

Abstract

Although the normal human placenta is impermeable to insulin, the effect of anti-insulin antibodies upon the placental barrier to insulin has not been defined. The placental transfer of human insulin-I125 was examined in normal (n=4) and insulin-dependent diabetic mothers (n=4) by infusing human insulin-I125 at a constant rate for 60-90 min. prior to delivery and measuring immuno-precipitable insulin-I125 radioactivity in the maternal and umbilical venous plasma at delivery. In normal mothers plasma insulin-I125 radioactivity was 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 capacity (1850-8400 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 insulin-dependent diabetic mother with negligible anti-insulin antibodies, no placental transfer of human insulin-I125 was demonstrated. Thus, in both normal and diabetic mothers, placental transfer of human insulin-I125 is negligible and the presence of maternal anti-insulin antibodies does not induce insulin transfer.