Differential channelling of liver lipids in relation to susceptibility to hepatic steatosis in two species of ducks.

In the human, hepatic steatosis can be associated with an imbalance between synthesis, secretion and storage of hepatic lipids, and exhibits a genetic susceptibility. The effect of overfeeding on hepatic lipid channelling was investigated in two genotypes of ducks that differ in their susceptibility to fatty liver, i.e. the common duck, Anas platyrhynchos, and the Muscovy duck, Cairina moschata. Before overfeeeding, the Muscovy duck exhibited a lower subcutaneous adiposity and a higher muscular development, whereas hepatic composition was similar in both genotypes (>5% lipids and triglycerides accounting for 6-10% lipids). In the plasma lipoprotein profile, HDL predominated (5.5-7.8 g/l) over VLDL (0.09-0.25 g/l) and LDL (0.65-1.06 g/l). All lipid and lipoprotein concentrations were lower in the Muscovy duck. In response to overfeeding, the Muscovy duck exhibited a higher degree of hepatic steatosis (62 vs. 50% lipids), and a lower increase in adiposity and in the concentration of plasma triglycerides (6-fold vs. 10-fold) and VLDL (23-fold vs. 34-fold). Thus, certain genotypes may be more responsive to the dietary induction of fatty liver because of a less efficient channelling of hepatic lipids towards secretion into plasma and adipose storage, and the duck may represent a suitable model in which to study the development of hepatic steatosis and its pathogenesis.

Effect of dietary fats on hepatic lipid metabolism in the growing turkey.

The influence of dietary fatty acids on hepatic capacity of lipid synthesis and secretion was investigated in 7-week-old male turkeys. They were fed 10% of either lard (rich in saturated and monounsaturated fatty acids) or linseed oil (rich in polyunsaturated fatty acids, especially 18:3n-3). Fattening was identical with both diets (0.15-0.20% of abdominal adipose tissue), but the proportion of muscle Pectoralis major was lower with linseed oil (6.6 vs. 7.4%). Specific activities of lipogenic enzymes (ME, G6PDH, ACX, and Delta9-desaturase) were not influenced by the diet, however, FAS activity was lower with linseed oil (14.3 vs. 25.4 nM NADPH fixed/min). Fasting concentrations of lipoproteins synthesized and secreted by the liver, VLDL and HDL, were also lower with linseed oil, as well as plasma concentrations of phospholipids and cholesteryl esters. However, when VLDL catabolism was inhibited by injection of an antiserum against LPL, VLDL concentration was identical in both groups (100-120 mg/l), whereas that of phospholipids and cholesteryl esters, that are transported by HDL mainly, remained lower with linseed oil. Thus, in the growing turkeys, and contrary to mammals and the chicken, feeding n-3 polyunsaturated fatty acids did not decrease hepatic triglyceride synthesis and secretion, nor fattening. By contrast, in this species, n-3 polyunsaturated fatty acids appear to influence mostly HDL metabolism, with a negative impact on muscular growth.