出版社：American Society for Biochemistry and Molecular Biology
摘要：A chylomicron-containing, low-density lipoprotein fraction of thoracic duct chyle ( Sf classes 20 and higher) obtained from rats fed either cholesterol-4-C14 or palmitic acid-1-C14 was injected intravenously into rats. Blood samples were obtained every 5 to 10 min for the first 1.5 hr, and thereafter at intervals of 30 min or longer up to 2.5 or 6.5 hr. The disappearance curves for the labeled cholesterol differed strikingly from those for the labeled triglyceride. The latter first declined rapidly and then more slowly. The former consisted of three phases: (1) rapid decline, (2) rising, and (3) leveling off. During the first phase, lipid-Cl4 disappeared from the circulation less rapidly after the labeled cholesterol injection than after injection of the labeled triglyceride. The percentage of lipid-C14 in the circulation increased about threefold during the rising phase of the cholesterol curves, and almost all of the terminal p1asma-C14 was present in the higher-density lipoproteins ( Sf classes less than 20). Disappearance curves derived for rats injected with cholesterol-C14 in the form of in vitro -prepared, higher-density plasma lipoproteins ( Sf classes less than 20) showed a gradual initial decline followed by a leveling off. The following conclusions were drawn from these and other available data: The first phase of the curves for the cholesterol-labeled, chylomicron-containing chyle fraction results from an initial rapid removal of cholesterol-C14 of chylomicrons accompanied by a slow removal of cholesterol-C14 that has been transferred intravascularly to higher-density lipoproteins. This phase, during which most of the chylomicron-cholesterol-C14 is removed from the circulation, is followed by a period during which labeled free sterol is rapidly recirculated from the liver as higher-density lipoproteins. The greater proportion of the labeled sterol in the plasma lipoproteins during the terminal phase is derived from the sterol that has been recirculated.
