Fatty acid metabolism and very low density lipoprotein secretion in liver slices from rats and preruminant calves

The liver of bovine animals possesses a low ability to secrete triglyceride s (TG) as part of the very low density lipoproteins (VLDL) compared with ra t liver, We compared hepatic fatty acid (FA) metabolism between rat and cal f in order to determine the limiting steps of TG-VLDL secretion in bovine a nimals. Liver slices from young Sprague-Dawley rats and preruminant Holstei n x Friesian calves were incubated for 7 h with increasing concentrations ( 0.1, 0.2, 0.4, and 0.8 mM) of [C-14]oleate. The oxidation of oleate to CO, and acid-soluble products was 2- to 3-fold higher in rat than in calf liver slices. Since oleate uptake was a-fold higher in rat than in calf, the oxi dation rate represented 20-29% of oleate uptake in both animal species. Ole ate was essentially incorporated into the neutral lipids (75-87% of total l ipids) 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 r at than in calf liver slices. Our results indicate that the slow rate of VL DL secretion by bovine liver is probably due to the limited availability of TG for VLDL packaging rather than to the preferential oxidation of FA.