EFFECTS OF ENERGY-BALANCE ON HEPATIC CAPACITY FOR OLEATE AND PROPIONATE METABOLISM AND TRIGLYCERIDE SECRETION

The purpose of this study was to identify conditions that could decrease accumulation of triglyceride in liver, perferably by increasing hepatic secretion of triglyceride-rich lipoproteins. Hepatocytes isolated from lactating goats were incubated in vitro, and the fate of [1-C-14]oleate was measured to determine hepatic capacity for various routes of long-chain fatty acid metabolism. The effect of in vivo energy balance and modifications of the nutrients present in the culture media were tested. Addition of linoleic acid, isovalerate, niacin, propionate, or propylene glycol did not affect triglyceride accumulation or secretion. Pyruvate decreased intracellular triglyceride accumulation. Changes in oxidation of oleate through manipulation of carnitine acyl transferase activity did not influence oleate esterification rate. Livers and hepatocytes isolated from goats in negative energy balance contained more lipid and triglyceride. Liver cells from goats in negative energy balance had decreased capacity for converting propionate to glucose with no change in ketogenic capacity as judged by acid soluble product formation from oleate. Hepatocytes from goats in negative energy balance retained less oleate as cell triglyceride with no change in triglyceride export, indicating a decreased net rate of esterification. Lacting goats, either in negative or positive energy balance, demonstrated the same low capacity for export of newly synthesized triglyceride as previously reported for fed wethers.