Studies on the in vivo transfer to retinoids from parenchymal to stellate cells in rat liver

Studies were conducted to examine the in vivo transfer of chylomicron (dietary) retinoid from rat liver parenchymal to stellate cells. We specifically addressed the question of whether chylomieron retinyl ester is transferred directly from hepatic parenchymal to stellate cells without first undergoing hydrolysis. [ 14 C]Retinyl palmitate and its non‐hydrolyzable ether analog, retinyl [ 3 H]hexadecyl ether, were utilized to answer this question. Chylomicrons labeled with these retinoids were injected intravenously into rats. Liver cell fractions, highly enriched in parenchymal or in stellate cells, were isolated 0.5 h, 4.5 h and 24 h after chylomicron injection. The ratio of 3 H: 14 C found in parenchymal cell preparations 4.5 h after injection was 1.8 times the ratio for the injected chylomicrons, and 24 h postinjection the ratio had increased to 2.5 times that of the chylomicrons. In the stellate‐cell‐enriched preparations the 3 H: 14 C ratio was found to be 0.39, 0.29, and 0.23 times the ratio found in the injected labeled chylomicrons at 0.5 h, 4.5 hand 24 h after injection respectively. From the levels of 14 C observed in the isolated stellate cells, it is estimated that 0.5 h, postinjection the stellate cells contained approximately 34% of the 14 C (i.e. the retinol injected as chylomicron retinyl ester) present in the liver. By 4.5 h the 14 C present in isolated stellate cells had risen to approximately 41% of that present in the total liver, and 24 h after injection approximately 55% of hepatic total 14 C was found in the stellate cells. These findings suggest that chylomicron retinyl ester is not transferred directly from the parenchymal to stellate cells without first undergoing hydrolysis to retinol.