HEPATIC GENE-EXPRESSION OF APOLIPOPROTEIN B100 DURING EARLY LACTATIONIN UNDERFED, HIGH PRODUCING DAIRY-COWS

The hepatic gene expression of apolipoprotein B, the major protein of very low density lipoproteins in plasma, was studied using 8 Holstein x Friesian cows during the first 12 wk of lactation. Cows were fattene d during gestation and were underfed just after parturition to increas e fat mobilization and subsequent hepatic steatosis. Intracellular con centrations of apolipoprotein B and apolipoprotein B mRNA and control parameters (albumin, total lipids, RNA, and proteins) were determined in liver samples obtained by biopsy from each cow on four occasions at 1, 2, 4, and 12 wk after calving. Results were compared with those ob tained from 5 dry cows in late pregnancy and 4 dry nonpregnant cows. T he hepatic concentration of apolipoprotein B was lower (approximately 25%) during wk 1, 2, and 4 after calving, a period of intense liver st eatosis (44.2 to 95.7 mg of triglycerides/g of fresh tissue), than for nonsteatotic dry cows (pregnant or nonpregnant); hepatic concentratio ns were also lower than those during wk 12. In contrast, hepatic conce ntrations of mRNA coding for apolipoprotein B, total proteins, RNA, an d albumin did not vary significantly during early lactation. These res ults suggested that synthesis of apolipoprotein B during early lactati on is specifically regulated at a posttranscriptional level by a decre ase in the rate of translation, or by a higher rate of intracellular d egradation of apolipoprotein B, or both.