Origin and characteristics of endogenous lipid in thoracic duct lymph in rat.

Thoracic duct lymph of rats eating a fat-free diet contained 7 mg of lipid per hr. The lipid was 70% triglyceride, and largely in the d < 1.006 lipoprotein fraction. Lipid of the d < 1.006 fraction of the lymph was many times more concentrated than that of the blood plasma at the same time. It reached the thoracic duct via lymphatics from the intestine; little entered from the liver. The fatty acid moiety composing over three-fourths of the lymph lipid mass was undoubtedly derived in part from bile lipid-possibly to the extent of roughly 50%, and in some part from other intraluminal materials. Studies with labeled palmitic acid indicated that little circulating free fatty acid was taken up by the intestinal mucosa and incorporated into lymph lipid.