HYPERRESPONSIVENESS TO DIETARY-CHOLESTEROL IN INBRED RABBITS IS NOT ASSOCIATED WITH ENHANCED REDUCTION IN BINDING OF BETA-VLDL TO LIVER MEMBRANES

In two inbred strains of rabbits with high or low response of serum ch olesterol to dietary cholesterol, binding of rabbit beta-VLDL to hepat ic membrane preparations was determined. The objective was to test the hypothesis that after cholesterol feeding, hyperresponders show a mor e dramatic reduction in hepatic apolipoprotein (apo) B/E receptors, wh ich may explain the development of the high degree of cholesterolemia in these animals. The number of hepatic high affinity receptors for be ta-VLDL in hyperresponders fed a diet without added cholesterol was, o n average, 20% lower than that in hyporesponders. After the addition o f increasing amounts of cholesterol to the diet, liver cholesterol con centrations were elevated to a greater extent in hyperthan in hyporesp onsive rabbits. Liver free cholesterol concentrations were negatively associated with maximal binding of beta-VLDL to liver membranes. With increasing liver free cholesterol concentrations, maximal binding was less effectively depressed in hyper- than hyporesponders. We conclude that in the inbred strains of rabbits, hyperresponsiveness to dietary cholesterol is not caused by enhanced depression of hepatic apo B/E re ceptors.