minor process. The latter results from a low liver cholesterol secretion in the bile due to the low hydrophobicity of its main bile acids. Furthermore, in this animal a high intestinal synthesis of cholesterol and apolipoproteins (particularly B 4 eJ is observed. The latter are secreted as very light lipoproteins (chylomicrons and VLDL) with a faster plasma turnover than the VLDL (apo8!!, E...) secreted by the liver. The &dquoremnants of rat VLDL are essentially very rapidly taken up by the

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... r their interplasmatic transformation pathway into IDL and LDL is not very significant ( 5 10°/). Man, who has a more significant hypercholesterolaemia after exogenous cholesterol ingestion ('hyperresponding&dquo subject) seems to have a less modulable capacity for transforming cholesterol into bile acids. This process accounts for only 50% of cholesterol output, faecal cholesterol excretion being quantitively just as significant. Cholesterol concentration and the cholesterol/bile acid ratio are much higher in human than in rat bile, the main bile acids being more hydrophobic. While both the intestine and liver contribute to cholesterogenesis, the relative importance of the latter is probably greater in man than in the rat Moreover, a larger fraction of plasma VLDL is transformed into IDL and LDL, the latter representing the main plasma cholesterol carrier. Determining whether the differences between the biodynamics of cholesterol processes in the rat and in man can be generalised to mammals with low or high sensitivities to hypercholesterolaemia and atherosclerosis seems to be a fundamental research objective for the next few years. compartmental analysis / cholesterol and bile acid biosynthesis / blliary cholesterol secretion / cholesterolaemia l apolipoprotein secretion