Abstract
A study was conducted to investigate hepatic uptake of retinyl palmitate-labelled chylomicron and intercellular transfer as well as intracellular translocation of retinoids in rat liver.
Following findings were obtained:
1) Kinetic analysis of the plasma disappearance curve of chylomicron which was labelled in vivo by retinyl palmitate revealed that three compartment model has given the best fit to the curve and that plasma retinyl palmitate was cleared predominantly through the compartment 2, while approximately one eighth of whole plasma retinyl palmitate disappeared through compartment 3 which kinetic constant was found to be about one sixth of that of compartment 2.
2) Twenty four hours after intraveneous injection of 14C-retinyl palmitate, 54% of the 14C taken up by the liver was found in stellate cells, and 86% of radioactivity in the stellate cell was already located in lipid droplets. Thus, it is suggested that, once received by the parenchymal cell, retinoid is rapidly transfered to the stellate cell and is deposited in the lipid droplets.
3) Of retinyl hexadecylether and retinyl palmitate, only the latter was found to be possible to transfer from parenchymal to stellate cells. Since retinyl hexadecylether is unable to be hydrolysed by retinyl palmitate hydrolase in parenchymal cells, it is strongly suggested that, following the uptake of retinyl palmitate by parenchymal cells, hydrolysis of the compound to retinol is essential to transport retinoids from parenchymal to stellate cells for storage.
