Insulin receptor binding from mid-term and full-term placentas of patients with gestational diabetes mellitus and normal pregnant women.

Insulin receptor binding was examined in the microvillous membranes of mid-term (20-22 weeks of gestation, MT) and full-term (FT) placentas from patients with gestational diabetes mellitus (GDM) and in normal pregnant control (N). Mid-term placentas were obtained from patients who have had spontaneous abortion. The maximum per cent specific binding (%SB) in MT placenta for GDM was significantly lower (4.8%) compared with the FT placenta (22%, p < 0.001), while in the N group the maximum per cent specific binding for MT placenta was 14.1% compared with 26% for the FT placenta (p < 0.001). Binding data from FT placenta of well-controlled GDM patients were similar with the FT placenta from N group (22% SB for GDM VS 26% SB for N). Even as there were similarities in the binding characteristics of FT placentas from both groups the placental membrane protein content in the GDM group was lower by 50% compared with the N control (2.5 +/- 0.11 VS 4.8 +/- 0.15 mg protein/g placenta respectively, p < 0.001) suggesting that in the GDM group achieving a tight glycemic control could improve receptor affinities. Data from the competitive binding assay of GDM patients showed that the insulin necessary to achieve 50% inhibition (ID50) was significantly lower in MT compared with the FT placenta (0.9 x 10(-9) M VS 3.8 x 10(-9) M, p < 0.001) but in the N placenta there was no alteration in the ID50 of MT and FT placentas (3.1 x 10(-9) M VS 4 x 10(-9) M, p < 0.01, respectively). The present study demonstrated that in GDM the placental insulin receptor binding was significantly lower in spontaneously aborted placenta compared with placentas collected at full-term. Furthermore, these data suggest that the objective to achieve a tight glycemic control in GDM patients could optimize insulin receptor function similar to that of a normal pregnancy. Thus a full term placenta from GDM patients under a well managed glycemic control throughout the entire duration of pregnancy would result in an optimum insulin receptor function.