SYNTHESIS AND SECRETION OF LIPOPROTEINS BY PRIMARY CULTURES OF RAT HEPATOCYTES

Synthesis and secretion of VLDL and LDL by primary cultures of rat hep atocytes maintained in serum free medium have been studied. A time-dep endent increase found in the [H-3]leucine labelled lipoproteins which floated at a density of 1.006 g/ml indicate the secretion of VLDL into the medium. That the hepatocytes also secrete LDL is shown by floatat ion of [H-3]leucine labelled lipoproteins by sequential centrifugation at a density range of 1.006-1.06 g/ml. Electrophoretic and immunoprec ipitation analysis show that about 60% and 65% respectively of H-3-rad ioactivity is associated with apoB in the two fraction of lipoproteins . At about 12hr 70-75% lipoproteins in the culture medium is in the VL DL density range and 25-30% is in the LDL density range. Conversion of secreted VLDL to LDL has also been shown by incubating hepatocytes wi th pre-labelled lipoproteins when there is a decrease in the fraction of VLDL range with a corresponding increase in the fraction of the LDL density range. Addition of glycosaminoglycans such as hyaluronic acid , chondroitin sulphate, and heparin into the medium cause significant increase in the synthesis and secretion of [H-3]apoB into the medium i ndicating a possible secretory control of apoB by local reuptake.