INSULIN-RECEPTOR BINDING FROM MIDTERM 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 fullterm (FT) placentas f rom patients with gestational diabetes mellitus (GDM) and in normal pr egnant 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 w ith 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 wel l-controlled GDM patients were similar with the FT placenta from N gro up (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 plac ental membrane protein content in the GDM group was lower by 50% compa red with the N control (2.5 +/- 0.11 VS 4.8 +/- 0.15 mg protein/g plac enta respectively, p < 0.001) suggesting that in the GDM group achievi ng a tight glycemic control could improve receptor affinities. Data fr om the competitive binding assay of GDM patients showed that the insul in 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, res pectively). The present study demonstrated that in GDM the placental i nsulin receptor binding was significantly lower in spontaneously abort ed placenta compared with placentas collected at full-term. Furthermor e, these data suggest that the objective to achieve a tight glycemic c ontrol in GDM patients could optimize insulin receptor function simila r to that of a normal pregnancy. Thus a full term placenta from GDM pa tients under a well managed glycemic control throughout the entire dur ation of pregnancy would result in an optimum insulin receptor functio n.