ObjectiveTo verify the expression change of insulin-like growth factor-Ⅰ (IGF-Ⅰ) protein and its mRNA before and after Roux-en-Y gastric bypass surgery (RYGB) in obese rats, and to investigate the relationship between the expression of IGF-Ⅰ and proliferation/apoptosis of adipose cells. Methods① Seventy male SD rats were raised at the SPF level circumstance and were randomly divided into control group (NC group, 10 rats) and high fat diet group (60 rats). Rats of high fat diet group were given specific high fat formula diet, rats of NC group were given particular formula diet. After 6 weeks, the body weights of the rats in high fat diet group were measured, and the 20 rats of top weight were selected. The 20 obese rats were randomly divided into 2 groups:gastric bypass (GB) group (n=10) and sham-operation group (SO group, n=10). RYGB were administered to the rats of GB group, and for rats of SO group, sham operations were performed. Rats of NC group did not receive any surgery. Inguinal adipose tissues[represented the subcutaneous adipose tissue (SAT)] and epididymal adipose tissues[on behalf of visceral adipose tissue (VAT)] were taken during operation in rats of GB group and SO group respectively (0.5 g), and 12 weeks after operation in all rats of three groups. The expressions of IGF-Ⅰ protein and its mRNA in adipose tissue were detected by Western blot and real-time fluorescence quantitative PCR. ② Transfection experiment. SAT cells were divided into blank control group (BC group, without transfection), IGF-Ⅰ(+) group (gene overexpression group), IGF-Ⅰ(+) empty vector group, IGF-Ⅰ(-) group (gene silencing group), and IGF-Ⅰ(-) empty vector group. Cells were transfected with corresponding vectors with 3 duplicated holes of each group. Cell viability and apoptosis assays were carried out in 48 hours after transfection. Expressions of protein kinase B (AKT), phosphorylated protein kinase B (p-AKT), phosphoinositide 3-kinase (PI3K), and phosphorylated phosphoinositide 3-kinase (p-PI3K) were detected by Western blot meanwhile. ③ Wortmannin experiment. SAT cells were divided into Wortmannin (+) IGF-Ⅰ(+) group, Wortmannin (+) IGF-Ⅰ(-) group, Wortmannin (-) IGF-Ⅰ(+) group, and Wortmannin (-) IGF-Ⅰ(-) group, which were transfected with corresponding vectors for 24 hours, then adding Wortmannin (0.1 mmol/L). After 24 hours, the expression levels of AKT, p-AKT, p-PI3K, PI3K, and GAPDH were detected by Western blot. Results① PCR results showed that, in SAT, compared with preoperative GB group, the expression levels of IGF-Ⅰ mRNA and its protein in postoperative GB group were both lower (P < 0.01). However, the expression levels of IGF-Ⅰ mRNA and its protein between preoperative SO group and postoperative SO group showed no significant difference (P > 0.05). In VAT, the expression levels of IGF-Ⅰ mRNA and its protein in 5 groups showed no significant difference (P > 0.05). ② The MTT results showed that, IGF-Ⅰ(+) group harbored stronger proliferation abilities compared with its negative control group (P=0.04), whereas IGF-Ⅰ(-) group had lower abilities compared with its negative control group (P=0.04). The results of flow cytometry assay showed that, the apoptosis rate of IGF-Ⅰ(+) group was lower (P=0.04) than that of the corresponding negative control group, and it was higher in IGF-Ⅰ(-) group than that of the corresponding negative control group (P=0.04). ③ Compared with IGF-Ⅰ(+) empty vector group, p-PI3K/PI3K ratio (P=0.03) and p-AKT/AKT (P=0.04) ratio of IGF-Ⅰ(+) group were increased; compared with IGF-Ⅰ(-) empty vector group, p-PI3K/PI3K ratio (P=0.04) and p-AKT/AKT ratio (P=0.04) of IGF-Ⅰ(-) group were decreased. The p-AKT/AKT ratio of Wortmannin (-) IGF-Ⅰ(+) group was higher (P < 0.05) than that of Wortmannin (+) IGF-Ⅰ(+) group; the p-AKT/AKT ratio of Wortmannin (-) IGF-Ⅰ(-) group was lower than that of Wortmannin (-) IGF-Ⅰ(+) group (P < 0.05). ConclusionsIGF-Ⅰ is involved in the accumulation of subcutaneous fat in rats. RYGB can significantly reduce the expression levels of IGF-Ⅰ mRNA and its protein in subcutaneous fat of rats, so as to achieve the effect of weight loss.