Hepatic delta 9 desaturation and plasma VLDL level in genetically lean and fat chickens.

Plasma VLDL (very low density lipoprotein) content and composition have been investigated in chickens from two lines selected for high or low abdominal fat/live weight ratio, and related to the activity of hepatic delta 9 desaturase. The amounts of plasma VLDL and VLDL-triglycerides (VLDL-TG) were significantly higher in the fat line than in the lean one. Moreover, the chemical composition of VLDL was different between lines, since the greater content of TG in VLDL in the fat birds was associated with lower proportion of all other components. The fatty acid composition of VLDL-TG exhibited differences between lines: palmitoleic acid, which results from hepatic delta 9 desaturation, was in higher proportions in the fat line, whereas linoleic acid was more abundant in the lean one. The activity of liver delta 9 desaturase was significantly higher in the fat animals. A positive correlation between plasma VLDL-TG concentration and hepatic delta 9 desaturase activity in the fat line animals strongly suggests that availability of monoenoic fatty acids is involved in the control of VLDL assembly and secretion. That latter process may explain some of the differences in plasma lipids and in adiposity of the two lines of chickens.