Decreased insulin binding to monocytes from normal pregnant women

To ascertain whether the decrease of glucose tolerance in pregnancy might be mediated by changes in insulin receptors, we have studied insulin binding to monocytes in 12 normal women during late pregnancy and 14 healthy, young, normal weight, nonpregnant female controls. The pregnant women had significantly higher fasting insulin concentrations in plasma than the controsl (18 +/- 3.5 vs. 8 +/- 1.1 microU/ml; P less than 0.01). Fasting concentrations of glucose and ketone bodies in plasma were not significantly different in the two groups. Insulin binding to monocytes from pregnant women was about 35% lower at each insulin concentration tested compared to the nonpregnant controls (P less than 0.01 at tracer insulin concentrations). Changes in cellular insulin binding were due to changes of the receptor number per cell, whereas the receptor affinity was unaffected. Insulin binding was not significantly correlated with the fasting plasma insulin in either of the two groups (P less than 0.1). Our results suggest that the deterioration of glucose tolerance in normal late pregnancy might be explained by a decrease of insulin sensitivity caused by a reduction of the number of insulin receptors.