Effect of High Fat Diets Containing No Cholesterol on the Properties of Rabbit Serum Lipoproteins and the Catabolism of Very Low Density Lipoproteins

154 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.New Zealand white rabbits were successively maintained on normal chow, a semisynthetic diet high in safflower oil (SAFF diet), and a semisynthetic diet high in hydrogenated coconut oil (COCO diet) for 9 weeks each.The -mobility of VLDL on agarose from rabbits fed the COCO diet indicates the presence of an altered lipoprotein particle which may be atherogenic. In addition, this VLDL was cholesteryl ester-enriched and triglyceride-poor. This alteration is perhaps explained by the stimulation of e novol cholesterogenesis in the liver. ALthough a similar effect has been reported after the cholesterol feeding of rabbits, the significance of the present studies is that while no dietary cholesterol was provided, an altered VLDL is produced with similar properties as those seen under conditions of both cholesterol-induced and human type III hyperlipoprotein-emias.When the SAFF diet was fed, the VLDL also became cholesteryl esterenriched and triglyceride-poor but it remained pre-beta in its mobility on agarose gels. In addition, this diet appeared to help prevent the hypercholesterolemic and hyperlipoproteinemic effects of the high saturated fat diet.Partially purified triglyceride lipase activities from postl-heparin plasma of both intact and supradiaphragmatic rabbit preparations were characterized using triglyceride emulsions as substrate. When radio-labeled VLDL from the experimentally-fed animals were used as substrate for these enzyme preparations, similar activities were observed whether preparations from intact or supradiaphragmatic rabbits were used. However, activities were lower than when normal chow-fed rabbit VLDL was assayed indicating that the VLDL from experimentally-fed animals is not as effective a substrate for the lipase enzyme. As a result, a build-up of the VLDL has been hypothesized under those dietary conditions which may be atherogenic. This finding is also consistent with the particle size of the various VLDL as estimated by surface to core ratios, the larger particles (i.e. chow-fed rabbit VLDL) being catabolized more rapidly.The preparation of VLDL remnants from VLDL of rabbits fed the various diets was also carried out. The remnants prepared from chow-fed rabbit VLDL were triglyceride-poor and cholesteryl ester-enriched. Loss of phospholipid and apo C peptides occurred while the free cholesterol content remained about the same. In addition, the mobility of these remnants on agarose was, for the most part, beta, while the VLDL originally showed pre-beta mobility. The VLDL from either SAFF-fed or COCO-fed rabbits was already appreciably cholesteryl ester-enriched and triglyceride-poor. Yet when remnants were prepared using either of these VLDL, it became further triglyceride-depleted and cholesteryl ester-enriched. Surface to core ratios of these VLDL remnants were different, indicating that the COCO diet-fed rabbit VLDL remnant was a larger particle than that in the SAFF case.Finally, the fatty acid composition of the VLDL was, in general, fund to reflect that of the diets fed. The fatty acid composition of VLDL remnants, however, showed preliminary evidence for the preferential hydrolysis of linoleic acid by the triglyceride lipase preparations when VLDL is the substrate.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD