Insulin binding to human adipocytes during late pregnancy in healthy, obese and diabetic state

As reported by other workers, late pregnancy is accompanied by an insulin-resistant state, which is not clearly explained by rising of the so-called gestational hormones. The present study reports the results on insulin binding and insulin action on adipocytes from healthy, obese and diabetic pregnant women (17 s.) isolated during Caesarian section and in control non pregnant women (22 s.). Glucose intolerance with hyperinsulinemia was shown in our healthy pregnant women but it was more evident in the obese pregnant women. Adipose cells' volume was larger than in non-pregnant state both in healthy and obese and diabetic pregnant women. Binding data, normalized to the same insulin concentration and cells number, indicated a decrease to the half of high affinity receptor sites with a slight decrease of total receptor numbers in healthy pregnant women; the obese and diabetic pregnant women showed a greater decrease in both affinity constants and receptor numbers. These data suggest that during pregnancy a decrease in receptor numbers and affinity constants takes place and is more evident in obese and diabetic pregnant women, giving a peripheral explanation to the insulin resistance itself. In this sense biological activity of isolated adipocytes gave a partial confirmation: glycerol release-inhibition in the presence of increasing amounts of insulin was decreased in obese and diabetic pregnant women in comparison with healthy pregnant women, but glucose-U-¹⁴C incorporation into adipose glycogen did not differ in the 3 groups. Because plasma insulin increases during pregnancy, the hypothesis of a down regulation of insulin-receptor by circulating insulin is confirmed by this research.