TISSUE DISTRIBUTION OF C14 AFTER THE INTRAVENOUS INJECTION OF LABELED CHYLOMICRONS AND UNESTERIFIED FATTY ACIDS IN THE RAT

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Abstract
Rats were injected intravenously with either rat chylomicrons, labeled in the triglyceride moiety with palmitic acid-1-C14, or with the unesterified labeled acid bound to serum albumin (UFA). Some of the recipient rats were fasted and some were carbohydrate-fed. They were killed 10 and 200 minutes after injection, and the tissues were analyzed for C14 content. Carbo-hydrate feeding spared the oxidation of both lipid forms and greatly increased the recovery of lipid-soluble C14. The tissue distribution of the chylomicron label was quite different from that of the UFA label. Most of the chylomicrons apparently do not undergo intravascular hydrolysis, and are probably removed intact from the circulation. Cleared chylomicron activity in the fasting state was found primarily in the liver and, after carbohydrate feeding, primarily in the depots. Plasma UFA rapidly exchanges with a tissue pool, which contains about 11 times as much exchangeable fatty acid as does the plasma. The fat depots are not a significant part of this pool, the bulk of which is in liver and muscle.