Distribution of vitamin A-storing lipid droplets in hepatic stellate cells in liver lobules--a comparative study

Abstract

To investigate the storage mechanisms of vitamin A, we examined the liver of adult polar bears and arctic foxes, which physiologically store a large amount of vitamin A, by high-performance liquid chromatography (HPLC), transmission electron microscopy (TEM) morphometry, gold chloride staining, fluorescence microscopy for the detection of autofluorescence of vitamin A, staining with hematoxylin-eosin (H&E), Masson's trichrome, and Ishii and Ishii's silver impregnation. HPLC revealed that the polar bears and arctic foxes contained 1.8-1.9 x 10(4) nmol total retinol (retinol plus retinyl esters) per gram liver. In the arctic foxes, the composition of the retinyl esters was found to be 51.1% palmitate, 26.6% oleate, 15.4% stearate, and 7% linoleate. The hepatic stellate cells of the arctic animals were demonstrated by TEM to contain the bulk of the vitamin A-lipid droplets in their cytoplasm. The liver lobules of the arctic animals showed a zonal gradient in the storage of vitamin A. The gradient was expressed as a symmetric crescendo-decrescendo profile starting at the periportal zone, peaking at the middle zone, and sloping down toward the central zone in the liver lobule. The density (i.e., cell number per area) of hepatic stellate cells was essentially the same among the zones. The gradient and the composition of the retinyl esters in storing vitamin A were not changed by differences in the vitamin A amount in the livers. These results indicate that the heterogeneity of vitamin A-storage capacity in hepatic stellate cells of arctic foxes and polar bears is genetically determined.