Changes in hepatic lipid parameters and hepatic messenger ribonucleic acid expression following estradiol administration in laying hens (Gallus domesticus)

Fatty liver hemorrhagic syndrome (FLHS) is characterized by increased hepatic triacylglycerol content associated with liver hemorrhages and results in a sudden decline in egg production. Genetic, environmental, nutritional, and hormonal factors have all been implicated in the etiology of FLHS, but the exact cause of FLHS is still unknown. Estrogens have been implicated in the development of excess fat content of the liver and in the etiology of FLHS. This study investigated estradiol (E₂) administration in hens and its effect on lipid metabolism. Hy-Line Brown laying hens were intramuscularly injected with E₂ on a daily basis for 3 wk. The dosages were 0, 0.5, and 1.0 mg/kg of BW, with corn oil injections used as a control. Egg production and quality were measured among the groups, with no significant difference seen in egg production. Liver weights of hens treated with E₂ were greater than those of control hens, but the increase was not statistically significant. Serum glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase activities and E₂ plasma concentrations increased in a dose-dependent manner, with plasma concentration of E₂ increasing from 6,900 to 19,000 pg/mL. No significant differences in free cholesterol or phospholipids were observed, but there was a significant increase in hepatic triacylglycerol levels. Injection with E₂ showed an increased expression of mRNA for peroxisome proliferator-activated receptor γ (23-fold), but not for peroxisome proliferator-activated receptor α. A statistically significant increase was seen for fatty acid synthase, apolipoprotein B, and adenosine triphosphate citrate lyase, but not for acetyl coenzyme A carboxylase, apolipoprotein VLDL-II, microsomal triglyceride transport protein, or malic enzyme. For proteins involved in the oxidation of E₂, only cytochrome P450 3A37 showed a statistically significant increase. The present results suggest that E₂ upregulates the synthesis of fatty acids and triacylglycerols and the accumulation of hepatic lipids by increasing mRNA expression related to lipid metabolism, and that excess E₂ in the blood leads to activation of E₂ catabolic metabolism (cytochrome P450 3A37)-related mRNA expression.