Low-density lipoprotein turnover in inbred strains of rabbits hypo- or hyperresponsive to dietary cholesterol

In two inbred strains of rabbits with high or low response of plasma cholesterol to dietary cholesterol, low density lipoprotein (LDL) apolipoprotein (apoLDL) kinetics were determined with the use of a heterologous tracer isolated from a Watanabe heritable hyperlipidemic (WHHL) rabbit. On a diet without added cholesterol, the total clearance of apoLDL (which equals apoLDL production) did not differ significantly between rabbits of both strains. After the feeding of a diet containing 0.1% cholesterol for six weeks, plasma LDL cholesterol, plasma apoLDL and liver cholesterol concentrations rose significantly in the hyperresponsive but not in the hyporesponsive rabbits. Cholesterol feeding depressed the total fractional catabolic rate (FCR) of apoLDL in the hyper- but not in the hyporesponsive rabbits; this was attributed to a decrease of receptor-dependent FCR while receptor-independent FCR was similar in the two strains. On the diet containing cholesterol, the receptor-mediated absolute catabolic rate (ACR) of apoLDL did not differ between hyper- and hyporesponsive rabbits but receptor-independent ACR of apoLDL was higher in hyperresponders. It is concluded that the higher plasma apoLDL levels in hyperresponsive rabbits fed the 0.1% cholesterol diet are caused by a higher production of apoLDL and not by a lower flux of apoLDL through the receptor-mediated pathway.