In vivo catabolism of human low density lipoprotein in the rat is mediated by a nonsaturable, low-affinity mechanism.

The degradation of human low density lipoprotein (LDL) was analyzed in fasted rats treated for 3 days with either 4-aminopyrazolo-(3,4-d)pyrimidine (4APP) or saline. Treatment with 4APP caused an 80% decrease in serum cholesterol concentration. The mono-exponential serum decay of a tracer amount of labelled LDL was changed neither by 4APP treatment, nor by the simultaneous injection of a bolus of unlabelled LDL. The sites of degradation of human LDL were determined using the nondegradable labelling compound O-(4-diazo-3-[125I]iodobenzoyl)sucrose (D125IBS). The sites of degradation and the rate of degradation of D125IBS labelled LDL were also not affected by 4APP treatment or by injection of a bolus of unlabelled LDL. It is concluded that human LDL is catabolised in the rat by way of a nonsaturable, low-affinity mechanism.