Formation of secondary fat particles from lymph chylomicrons in the dog

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Abstract
To test whether the secondary fat particles observed in plasma during fat absorption are derived from the liver, constant intraportal infusions of fresh, unrefrigerated C14-labeled lymph were given to dogs. Secondary particles were isolated from hepatic vein plasma. Specific activity of secondary particle trigly-ceride (TG) ranged from 50 to 80% of that of the infused lymph chylo-micron TG; however, in each dog, secondary particle TG specific activity remained constant throughout the infusion. Thus, it appeared that secondary particles were not formed in vivo as a result of gradual mixing of lymph chylomicrons with hepatic TG. An investigation of the role of plasma in secondary particle formation revealed that secondary particles were produced in a peripheral artery, during infusion of lymph into the artery proximally in a hepatectomized, partially eviscerated dog, in lymph, during the earliest phase of fat absorption following a 72-hr fast, and in vitro as a result of combination of lymph with plasma. These results are consistent with the hypothesis that secondary particles are formed as a result of the interaction of lymph chylomicrons with a plasma TG-containing lipoprotein.