The effects of HDL1 lipoprotein infusion on biliary lipid secretion were studied in the in vitro model of rat perfused liver. A strong increase in bile flow was observed during and after lipoprotein infusion. This caused a significant rise in cholesterol, phospholipid and bile salt secretions. However, only the percentage of cholesterol increased with respect to the other bile lipids. The changes observed in the cholesterol/phospholipid molar ratio values of liver membrane subfractions (i.e., liver plasma membrane, mitochondria plus lysosomes and microsomes) isolated from the perfused rat liver after HDL1 administration were not significant.

In female frogs ( Rana Esculenta ) during gametogenesis the cholesterol synthesized in the liver by 3-hydroxy-3-methylglutaryl coenzyme A reductase is mostly exported into the blood and taken up by the oocytes. In order to understand the fate of the neosynthesized cholesterol, female and male frogs and estrogenized male controls were injected with the labelled precursor 14 C mevalonate. In females and in estrogenized controls, mevalonate-derived radioactivity is found in a plasmatic lipoprotein that has been identified as vitellogenin by immunological detection. The increased 3-hydroxy-3-methylglutaryl coenzyme A reductase activity present in females in Fall is likely to be committed to provide cholesterol for the lipidation of this cholesterol-rich protein.

Sixteen hours after partial hepatectomy in the rat, the synthesis of mevalonate (MVA) is not committed to produce cholesterol and only partially utilized for dolichol formation. In order to investigate the fate of MVA in this replicative system, slices of the remaining liver were incubated with 5- 3 H-MVA. Labeled proteins from whole liver and purified nuclei were analyzed after extensive delipidation and separation by SDS-PAGE. Many MVA-derived proteins were identified at 16 hours, while only two labelled peptides were detectable at 24 hours. The radioactivity was localized in covalently bound lipid moieties. A highly labeled 26 kD peptide was detectable in the nucleus at 16 hours, suggesting its involvement in the cell cycle progression.