| Summary: | A cholesterol-4-C14-labeled, very low-density, lipoprotein fraction of chyle was injected into heparin-treated and control rats. The disappearance of the C14 from the whole blood was followed at intervals up to 25 min after the injection. Heparin increased the rate at which the injected cholesterol-C14 left the circulation during the first 10 min. Determination of the distribution of isotope among ultracentrifugally separated Sf > 20, Sf 0–20, and high-density plasma lipoproteins revealed that, at 10 min after the administration of the cholesterol-labeled chyle preparation, a much greater proportion of the plasma lipid-C14 was present in the Sf 0–20 lipoproteins isolated from the heparin-treated than from the control rats. The in vitro mixing of the cholesterol-labeled, very low-density chyle lipoproteins with blood obtained from heparin-treated and control rats also resulted in recovery of a disproportionately high percentage of the isotope in the Sf 0–20 lipoproteins of the heparin-treated rats. Such a distribution of isotope among the plasma lipoproteins in heparin-treated rats is compatible with the scheme of Lindgren and co-workers for the action of clearing factor lipase in which chylomicrons are degraded through a series of lipoprotein complexes to lipoproteins of the Sf 0–20 class, the cholesterol and phospholipid components of the original chylomicrons becoming part of the final end products. A very rapid removal of any of the lipoproteins resulting from the heparin-induced lipolysis could account for the effect of heparin on the disappearance of the injected cholesterol-C14 of the chyle lipoproteins from the circulation.
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