Regulation Of Expression Of Low Density Lipoprotein Receptor In Liver Of Periparturient Dairy Cows

The Periparturient period of cow is generally defined as 2-3 wk before calving to 2-3 wk after calving. Ketosis and fatty liver based on energy metabolism disorder are the common diseases. LDLR are of key constitutive protein and regulatory protein for assembly and secretion of VLDL which is possible mechanisms for decreased triacylglyceride transfer in cows with fatty liver.In this study, healthy multiparous periparturient dairy cows, primary hepatocyte culture in vitro, and quantitive RT-PCR were applied to probe the effects of energy state, neuroendocrine and metabolites on low density lipoprotein receptor in liver of periparturient dairy cows.Animal raising trial: thirty Chinese peripartum Holstein cows, with milk yield about 7000Kg, 5-8yrs and 3-5 parities, were randomly assigned into three different energyintake treatments, each of 10, fed with 100% energy diet (100% energyintake of nutrition needs of China Dairy Cow Raise Standard 2000, control group), 120% energy diet and 80% energy diet at 28 days before parturition, respectively. After parturition, all the cows were offered criteria lactating day provisions until 56 days postpartum. All cows were fed curved hay and corn silage firstly, then concentrates daily at 6:00,12:00 and 19:00. The cows were fed individually and had free access to tap water. During the experimental period, expression level of LDLRmRNA in liver were determined from 28d and 14d antepartum to 1d, 14d, 28d and 56d postpartum. The results were as follows: The level of liver LDLRmRNA in the peripartum was upregulated significantly in cows fed with low energy diet during the dry period. The mean abundance of liver LDLRmRNA after calving was upregulate significantly in cows fed with standard and high energy diets during the dry period, and was significant lower than that of low energy diet. 14d after parturition, the liver LDLRmRNA abundance in all cows was decreased significantly by increased liver TG content after calving. The expression level of liver LDLRmRNA may be one of the major regulation factors of the assembly and secretion of VLDL in liver of dairy cows during the early lactation, but the cause of upregulated LDLRmRNA abundance in the peripartum in cows fed with low energy diet during the dry period needs to be further investigated.Primary hepatic cell culture in vitro trial: new born calves were killed by carotid artery bloodletting. Under the condition of asepsis, liver posterior lobe was collected, then sheared and digested for separating hepatocytes. Cells were seeded (l×10~6) onto custodite cell culture dishes with polylysine. After attachment, semiquantitative RT-PCR were employed to determine the expressing level of LDLR mRNA in primary hepatocytes which were treated with different concentrations of insulin (0 nmol/L, 1 nmol/L, 10nmol/L, 100 nmol/L, 1000 nmol/L), glucagons (0 nmol/L, 1 nmol/L, 10nmol/L, 100 nmol/L, 1000 nmol/L) and leptin (0 ng/mL, 2.5ng/mL, 5 ng/mL, 10 ng/mL, 50 ng/mL). The results showed that: ①the expression level of LDLR mRNA in hepatocytes was gradually increased with increasing concentration of insulin in cell culture media; ②Depressed expression of LDLR mRNA in...