The metabolic modification of low-density lipoproteins in normal and hypercholesterolaemic guinea pigs.

1. Low-density lipoproteins were isolated by ultracentrifugation from the serum of guinea pigs that were fed either on a normal diet, or on a diet supplemented with corn oil and cholesterol. 2. After labelling with tracer amounts of radioactive iodine, these lipoproteins were injected into the bloodstream of guinea pigs that were fed either on the normal or on the supplemented diet. 3. In all cases, the density of the labelled lipoproteins was increased by exposure for 24-48 h to the metabolic processes of the guinea pig. 4. The final density reached by lipoproteins isolated from fat-fed guinea pigs was less than that reached by lipoproteins from normal animals. 5. Fat-fed guinea pigs were unable to increase the density of either normal lipoproteins, or those from fat-fed guinea pits, to the same extent as animals fed on the normal diet. 6. It is concluded that the lipid-rich diet brings about a modification of lipoprotein metabolism in the guinea, pig, which plays an important part in determining the nature of the nature of the low-density lipoprotein that is present in the plasma.