Low density lipoprotein turnover in swine

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Abstract
The catabolism of i.v. injected 125I-labeled low density lipoproteins (LDL) was followed in normal miniature swine for 2 wk. When compared with the 2-exponential model, the decay curve of the plasma radioactivity associated with the LDL fraction was best described by a 3-exponential model. The half-lives were 4.5 .+-. 3.7, 19.7 .+-. 6.6 and 127 .+-. 70 h (mean of 4 studies). Assuming a kinetic model with metabolism of LDL in the rapidly equilibrating compartment and 2 slower equilibrating compartments (a model requiring 3 exponentials), the mean fractional catabolic rate for apo-LDL was calculated to be 0.015 h-1. Therefore at steady state the synthetic rate for apo-LDL in the same pigs would be 5.6 .+-. 4.1 mg/h. Different kinetic models using 2 or 3 exponentials would provide different values for the synthetic rate of apo-LDL. In view of the known existence of at least 3 major equilibrating pools for LDL in plasma, liver and lymph, and in view of the present results, the kinetic model for LDL metabolism is better represented by a 3-exponential system.