Lecithin:Retinol Acyltransferase and Retinyl Ester Hydrolase Activities Are Differentially Regulated by Retinoids and Have Distinct Distributions between Hepatocyte and Nonparenchymal Cell Fractions of Rat Liver

摘要

The cellular distribution of enzymes that esterify retinol and hydrolyze retinyl esters (RE) was studied in liver of vitamin A–sufficient,–deficient, and deficient rats treated with retinoic acid or N-(4-hydroxyphenyl)-retinamide. Livers were perfused and cell fractions enriched in hepatocytes, and nonparenchymal cells were obtained for assays of RE and enzyme activity. The specific activity of lecithin:retinol acyltransferase (LRAT) was approximately 10-fold greater in the nonparenchymal cell than the hepatocyte fraction from both vitamin A–sufficient and retinoid-treated rats. Total RE mass, newly synthesized [3H]RE and LRAT activity were positively correlated in liver and isolated cells of both normal (P 0.0001) and retinoid-treated rats (P 0.0002). In nonparenchymal cells, these three constituents were nearly equally enriched as evaluated by their relative specific activity values (RSA, defined as the percentage of recovered activity divided by the percentage of recovered protein), which were each significantly greater than 1.0, with values of 4.3 for total RE mass (P 0.05), 3.6 for newly synthesized [3H]RE (P 0.01) and 3.8 for LRAT activity (P 0.01). In contrast, the specific activities of neutral and acid bile salt–independent retinyl ester hydrolases (REH) did not vary with vitamin A status, and their RSA values were close to 1.0 in both hepatocytes and nonparenchymal cells. These data show that LRAT and REH are differentially regulated by retinoids and that these enzymes also differ in their spacial distribution between liver parenchymal and nonparenchymal cells.