Effect of sex and bezafibrate on incorporation of blood borne palmitate into lipids of rat liver nuclei

The aim of the present study was to investigate whether lipid metabolism in the nuclei is affected by changes in the metabolism of free fatty acids in the liver. The experiments were carried out on 3 groups of rats: 1 - contr ol-male, 2 - female, and 3 - male, treated with bezafibrate (a peroxisome p roliferator). The rats received (1)4C-palmitic acid intravenously. Thirty m in later liver samples and blood from the abdominal aorta were taken. The l iver nuclei were isolated in sucrose gradient. Lipids were extracted from t he nuclei and the liver homogenate and subsequently separated into the foll owing fractions: phospholipids, mono-, di- and triacylglycerols, free fatty acids, cholesterol and cholesterol esters. The radioactivity of each fract ion was counted. Furthermore, the content of free fatty acids and the fatty acid binding proteins was measured. It was found that radioactivity was pr esent in each lipid fraction obtained from the liver homogenate and from th e nuclei. In the female group, the total radioactivity of lipids in the liv er homogenate was lower, whereas in the nuclei it was higher in comparison to the male group. The reduction in the radioactivity in the liver was most ly accounted for by decreased radioactivity in the fraction of triacylglyce rols and phospholipids. In the nuclei, the radioactivity of the fraction of phospholipids, free fatty acids and diacylglycerols was elevated. Bezafibr ate did not affect the total radioactivity of lipids in the liver and reduc ed it in the nuclei. In the liver, the drug increased radioactivity mostly in the fraction of phospholipids and reduced it mainly in the fraction of t riacylglycerols. In the nuclei, the radioactivity of each lipid fraction ex amined was reduced. The content of the fraction of free fatty acids in the liver and in the nuclei in the female and in the bezafibrate-treated groups did not differ from the respective value in the control group. The content of fatty acid binding proteins in the nuclei of the female and bezafibrate -treated groups increased in parallel to the elevation in their content in the cytosol. It is concluded that the female sex hormones and bezafibrate i nfluence the transport of selected lipids into the nuclei. The effects seem to be a consequence of the action of these factors directly on the nucleus .