Abstract： Objective To investigate the variations of the expression and activity of phosphatidyl inositol-3 kinase(PI-3K)in the adipose tissue of pregnant women with gestational diabetes mellitus(GDM)and to explore its relationship with insulin resistance(IR)in these women.Methods The expression of PI-3K p85aprotein and mRNA in adipose tissue were detected by Western blot and Semi quantitative reverse transcription polymerase chain reaction(RT-PCR)in 20 GDM women(GDM group)and 20 normal pregnant women(normal group).The activity of PI-3K was determined by ELISA and IR index was calculated using homeostasis model assessment(HOMA)according to the results of fasting insulin(FINS)and fasting plasma glucose(FPG),which measured by oxidase assay and immunoradioassay,respectively.Results The expressions of PI-3K p85αmRNA and PI-3K p85a protein were markedly increased in the adipose tissue of GDM group than in the normal group(mRNA:0.83±0.03 vs 0.53±0.07,P＜0.01;protein:0.93±0.04 vs 0.71±0.06,P＜0.01).However,the PI-3K activity in the GDM groups was significantly down-regulated compared with the normal group(1.7±0.6 vs 5.2±0.5,P＜0.01).The levels of FPG and FINS (HOMA-IR)in the GDM group were all significantly higher than the normal group[FPG:(5.8±0.2)mmol/L vs(4.7±0.3)mmol/L;FINS:(14.8±0.2)mmol/L vs(11.2±0.3)mmol/L;HOMA-IR:1.3±0.4 vs 0.9±0.3,a11 P＜0.01]. Conclusions The decreased activity of PI-3K in the adipose tissue may be one of the molecular mechanisms for IR in GDM.