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

The cellular distribution of enzymes that esterify retinol and hydroly ze retinyl esters (RE) was studied in liver of vitam in A-sufficient,- deficient, and deficient rats treated with retinoic acid or N-(4-hydro xyphenyl)-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 acyl transferase (LRAT) was approximately 10-fold greater in the nonparench ymal cell than the hepatocyte fraction from both vitamin A-sufficient and retinoid-treated rats, Total RE mass, newly synthesized [H-3]RE an d LRAT activity were positively correlated in liver and isolated cells of both normal (P < 0.0001) and retinoid-treated rats (P < 0.0002), I n nonparenchymal cells, these three constituents were nearly equally e nriched as evaluated by their relative specific activity values (RSA, defined as the percentage of recovered activity divided by the percent age 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 sy nthesized [H-3]RE (P < 0.01) and 3.8 for LRAT activity (P < 0.01). In contrast, the specific activities of neutral and acid bile salt-indepe ndent retinyl ester hydrolases (REH) did not vary with vitamin A statu s, and their RSA values were close to 1.0 in both hepatocytes and nonp arenchymal cells. These data show that LRAT and REH are differentially regulated by retinoids and that these enzymes also differ in their sp acial distribution between liver parenchymal and nonparenchymal cells.