Rat apolipoprotein A-IV metabolism

Earlier studies by Van 't Hoeft et al. (85, 160), in our laboratory, mainly focussed upon the catabolism of HDL apolipoproteins A-I and E. They found that the kidneys were an important organ involved in the catabolism of these proteins together with the liver. The present thesis mainly deals with HDL apo A-IV. Until very recently, apo A-IV metabolism was relatively unknown. This was due to the fact that, during isolation of HDL particles by density ultracentrifugation, apo A-IV was readily "stripped" and recovered in the "bottom" fraction, together with the bulk of the serum protein. Better isolation procedures enabled us to investigate the behaviour of apo A-IV in the rat, leading to expansion of our knowledge of lipoprotein metabolism in general. The first part (Chapter 2) outlines a sensitive electroimmunoassay for the determination of apo A-I, apo E, and apo A-IV in diluted samples. This method has been successfully used to analyse the distribution of these proteins in rat mesenteric lymph (Chapter 3) and rat serum (Chapter 4), following their fractionation by molecular sieve chromatography on agarose gels. The latter procedure was employed to obviate the well known problem of particle protein stripping which occurs during ultracentrifugation (60, 86-88). Chapter 4 describes the results of a study designed to compare the effects of gel filtration and ul tracentrifugation on HDL particle composition. Chapters 5 and 6 describe our studies on the catabolic sites of apolipoprotein A-IV containing lipoproteins. The final paper (Chapter 7) describes the analysis of HDL subclasses using specific immunoprecipitation.