When 14C-labelled chylomicron lipid is injected into the circulation of the supradiaphragmatic portion of the fasting rat a composite disappearance curve which can be represented by two exponential components is obtained. The dominant component, which accounts for the removal of over 90 % of the injected label, has a short half-life similar to that observed for the triglyceride fatty acids of injected chyle in intact animals. The minor component has a much longer half-life and may be accounted for, at least in part, by the presence of 14C-labelled material in phosphatides and cholesterol esters in the plasma. At 40 min after the injection of the chylomicron lipid, when over 90 % of the dose has left the circulation, most of the labelled material can be recovered in the muscle and skin. Very little radioactivity is present in the brain. Oxidation of the labelled material appears to occur more rapidly in the fasting than in the fed state. Endogenous triglycerides in d < 1.006 lipoproteins are removed from the plasma at a similar rate to injected chylomicron lipid. Triglyceride in d > 1.006 lipoproteins are removed much more slowly. Free fatty acids are removed from the circulation of the supradiaphragmatic portion of the rat with a half-life of 1.5 min. The significance of these findings is discussed in relation to current concepts of fatty acid transport.
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Bezman-Tarcher et al. (1965) studied this question.