Graulet B, Gruffat D, Durand D, Bauchart D
Laboratoire Croissance et Métabolismes des Herbivores, Unité Métabolismes Energétique et Lipidique, Institut National de la Recherche Agronomique, Centre de Recherches de Clermont Ferrand-Theix, 63122 Saint Genès-Champanelle,
J Biochem. 1998 Dec 1;124(6):1212-9. doi: 10.1093/oxfordjournals.jbchem.a022240.
The liver of bovine animals possesses a low ability to secrete triglycerides (TG) as part of the very low density lipoproteins (VLDL) compared with rat liver. We compared hepatic fatty acid (FA) metabolism between rat and calf in order to determine the limiting steps of TG-VLDL secretion in bovine animals. Liver slices from young Sprague-Dawley rats and preruminant Holstein x Friesian calves were incubated for 7 h with increasing concentrations (0.1, 0.2, 0.4, and 0.8 mM) of [14C]oleate. The oxidation of oleate to CO2 and acid-soluble products was 2- to 3-fold higher in rat than in calf liver slices. Since oleate uptake was 2-fold higher in rat than in calf, the oxidation rate represented 20-29% of oleate uptake in both animal species. Oleate was essentially incorporated into the neutral lipids (75-87% of total lipids) that were stored mainly in the cytosol in both animal species (81-90% of neutral lipids). The accumulation of neutral lipids in the cytosol was 3.4-fold higher while VLDL secretion was 6- to 18-fold more efficient in rat than in calf liver slices. Our results indicate that the slow rate of VLDL secretion by bovine liver is probably due to the limited availability of TG for VLDL packaging rather than to the preferential oxidation of FA.
与大鼠肝脏相比，牛的肝脏分泌极低密度脂蛋白（VLDL）中甘油三酯（TG）的能力较低。我们比较了大鼠和小牛肝脏脂肪酸（FA）的代谢情况，以确定牛肝脏中TG-VLDL分泌的限制步骤。将幼年Sprague-Dawley大鼠和反刍前的荷斯坦×弗里生小牛的肝脏切片与浓度递增（0.1、0.2、0.4和0.8 mM）的[14C]油酸一起孵育7小时。油酸氧化为CO2和酸溶性产物的速率在大鼠肝脏切片中比在小牛肝脏切片中高2至3倍。由于大鼠对油酸的摄取量比小牛高2倍，因此两种动物的氧化率均占油酸摄取量的20-29%。油酸主要被掺入中性脂质中（占总脂质的75-87%），两种动物的中性脂质主要储存在细胞质中（占中性脂质的81-90%）。细胞质中中性脂质的积累在大鼠肝脏切片中比在小牛肝脏切片中高3.4倍，而VLDL分泌效率则高6至18倍。我们的结果表明，牛肝脏VLDL分泌速率缓慢可能是由于用于VLDL包装的TG可用性有限，而不是由于FA的优先氧化。
