We characterized the lipoproteins produced by perfused rat liver in recirculating system. The catabolic rate of the perfusate VLDL in vivo was faster than that of the LDL. The electrophoretic mobilities of both lipoproteins on agarose gel were at alpha mobility, though addition of serum to them resulted in the beta mobility. These observations suggest that VLDL and LDL are produced by the liver independently and that these lipoproteins were secreted as negatively charged.
Cholesterol feeding resulted in an increased hepatic production of VLDL by several folds but a decrease in the production of LDL. The distribution of radioactivity among VLDL apolipoproteins was not affected by cholesterol feeding. On the other hand, incorporation of radioactivity into apo B-100 of LDL decreased significantly. Hepatic synthesis of apo B, which was estimated by the immunoprecipitable radioactive apo B in the liver, was decreased significantly by cholesterol feeding. This is the first report of the down regulation of apo B synthesis by cholesterol feeding. The decrease in apo B could be the reason of the fatty liver observed in the cholesterol feeding.
