Storage of vitamin A in extrahepatic stellate cells in normal rats

Abstract

In mammals, vitamin A is primarily stored as retinyl esters in hepatic stellate cells under normal dietary intake of the vitamin. Previously, extrahepatic vitamin A-storing stellate cells have only been identified in animals maintained on a vitamin A-rich diet, and it has not been known whether these cells play a role in normal vitamin A metabolism. The purpose of this study was, to quantify the stellate cell lipid droplet area in hepatic and extrahepatic stellate cells in control rats and in rats fed excess vitamin A. The stellate cells were identified by the gold chloride staining technique, specific autofluorescence of retinyl ester, and by electron microscopy. The stellate cell lipid droplet area was then quantitated by the use of morphometric quantitation. We demonstrated that lipid droplet-containing stellate cells were identified in liver, lung, kidney, and intestine, in normal as well as vitamin A-fed rats. The area of lipid droplets in liver, lung, and intestine stellate cells of normal rats was 0.2, 0.3, and 0.04 mm2 per cm2 tissue, respectively. When the rats were administered excess vitamin A, the hepatic, lung, and intestinal stellate cell lipid droplet area increased about 10-fold, 2-fold, and 40-fold, respectively. Thus the present study shows that extrahepatic stellate cells in lung and intestine of normal rats contain lipid droplets, and that these lipid droplets increase in area when high doses of vitamin A are fed to the animals. These data suggest that not only liver stellate cells but also extrahepatic stellate cells play an important role in vitamin A storage in normal as well as vitamin A-fed animals.