The effect of fatty liver induction with estradiol injection on expression of insulin resistance-related genes in liver of post-peak laying hens

To investigate the effect of fatty liver on insulin resistance in the liver of laying hens, an experiment using 80 laying hens of commercial line strains (w-36) after peak production (age 43 weeks) for eight weeks were performedin a completely randomized design with two treatments. The experimental treatments included control group (no injection) and the estradiol group  (injection of two mg estradiol benzoate per kg body weight). In order to induce fatty liver disease, the injection of 17-beta estradiol started from the third week of experiment (age 46), and was performed three times a week for 21 days. Blood samples were taken to evaluate the concentration of triglycerides, cholesterol and liver enzymes (aspartate transaminase (AST), alanin transaminase (ALT) and alkaline phosphatase (ALP) at the end of the experiment using 20 hens from each treatment. At the end of experiment, five hens of each treatment were selected and sacrificed, then 50 g of liver tissue was removed to study gene expression of insulin receptor (InR), glucose transporter1 (Glut1), sterol regulatory element binding protein (SREBP1), Ribosomal S6 kinase1 (S6K1), Target of Rapamycin (TOR) and Forkhead box protein O1 (FOXO1). The results showed that the injection of estradiol induced fatty liver and increased plasma concentrations of cholesterol and triglyceride as well as activity of AST, ALT and ALP.  In hens with fatty liver, expression of FOXO1 (4.1-fold), TOR (3.9-fold), S6K1 (3.3-fold) genes increased, and conversely, expression of InR (4.6-fold), Glut1 (7.5-fold) decreased. In conclusion results of the present study showed that the fatty liver induction in laying hens increased expression of insulin resistance-related genes.