The metabolic fate of cholesterol delivered to rat hepatocytes by rat plasma lipoproteins was determined. Binding and degradation of rat low and high density lipoproteins (LDL and HDL) in rat hepatocytes were studied. ¹²⁵I-labelled LDL and HDL were incubated with cells in the presence of varying concentrations of unlabelled lipoproteins for two hours at 37°C. The amount of ¹²⁵I-LDL and ¹²⁵I-HDL binding and degradation decreased by increasing concentrations of respective unlabelled lipoproteins. The presence of 50-fold excess of unlabelled LDL or HDL resulted in a reduction of ¹²⁵I-LDL and ¹²⁵I-HDL bindings by 66-82%, and degradations by 63-88%, respectively. Equilibrium dissociation constants (K [subscript d]) determined by Scatchard analysis for HDL (.15 x 10⁻⁸M) and LDL (1.04 x 10⁻⁸M) revealed that HDL have approximately 7-fold higher binding affinity for receptors on cell surface than LDL. Specific use of LDL and HDL-cholesterol for bile acid synthesis by rat hepatocytes was investigated. When LDL and HDL labelled with ³H-LDL cholesterol was transformed to bile acids mostly as lithocholic, chenodeoxy and deoxycholic acids. A technique developed for isolation of hepatocytes from rat liver was described. Once isolated by the technique most cells retained their microscopic structural integrity, and excluded trypan blue. The viability was 93%, which decreased to 86% after four hours of incubation. The presented data demonstrated that both HDL and LDL bind to specific receptors on hepatocytes and undergo proteolytic degradation in rats. The study also showed that the binding affinity of HDL to hepatic receptors was much greater than that of LDL but in total binding LDL uptake was four times greater than HDL, suggesting the presence of two specific binding sites for HDL and LDL. The first direct evidence for the preferential utilization of HDL-cholesterol for biosynthesis of bile acids in vivo is presented. This finding is compatible with the current concept of HDL as the protective lipoprotein against developing coronary heart disease. / Graduation date: 1985

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Three (intact) Angus males and three females which were half-sibs and born within 21 days of each other were selected for this study. Each animal was bled and biopsied periodically from suckling calves to mature slaughter weights, to determine the qualitative composition of lipoproteins and to differentiate the lactate lipogenic activity of subcutaneous tissue during growth and development. At slaughtered, a sample of intramuscular adipose tissue was taken to determine the lactate lipogenic activity at this location. Two days later, one side of each carcass was separated into wholesale cuts. Each wholesale cut was dissected into separable bone and soft tissue and sampled for protein, lipid and moisture determinations. The elution profiles of lipoproteins were similar for all animals. Major peaks observed were (1) very low density (VLDL), (2) low density (LDL) and (3) high density lipoproteins (HDL). Triglycerides, cholesterol and protein were not significant (P < .05) between males and females for the VLDL. At one year of age, females had large (P < .05) amounts of protein for the HDL. In both groups of cattle, largest (P > .05) amounts of protein were greater in the HDL at 9 months of age. Profiles of HDL apoproteins at all ages showed that in both groups of cattle, a distinct band with a weight of about 28,000 was present representing apo-AI. Apo-protein components of pooled LDL fractions showed a protein which was unable to enter the acrylamide gel (7.5 – 20%) used. The component may represent apo-B with a molecular weight of about 250,000. The lactate lipogenic activity of subcutaneous adipose tissue was larger in the males and only significant (P < .05) at 9 months of age. The lipogenic activity was higher (P > .05) in the subcutaneous tissue when compared to the intramuscular tissue at slaughter. In both cases, males showed to use more (P > .05) lactate for fatty acid synthesis in intramuscular and subcutaneous tissue than the females. Magnitude of quality and yield for carcass traits were better for the males than females. Bone, meat and lean weights were significantly (P < .05) greater for the males, however, on a percentage basis per side weight, differences were eliminated. In addition, no significant (P > .05) effect was present between male and female wholesale and side carcass composition.

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by Wai-kee Cheung. / Bibliography: leaves 307-332 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1984