Abstract
Effects of retinyl palmitate, thyroxine and ethanol on hepatic uptake and release of vitamin A (A) were studied in rat liver perfused with fluorocarbon emulsion. The liver of growing rats fed a normal diet or A-deficient diet was perfused in situ with retiryl palmitate and the uptake of retinyl palmintate from the perfusate and the release of retinol to the perfusate were estimated by HPLC. A rapid uptake of retinyl palmitate by the liver in normal and A-deficient rats was shown. The release of retinol from the liver without retinyl palmitate was singificantly lower than that in the normal and A-deficient groups with retinyl palmitate. Rat retinol-binding protein (RBP) normally circulates in the serum as a protein-protein complex together with prealbumin (PA). And so, this study was conducted whether the retinol present in the perfusate of normal rat was also present in the form of RBP-A-PA or RBP-A. The perfusate from the normal rats were chromatographed of Sephadex G-100 columns, and the elution volume of immunoreactive RBP was determined. The results indicated the retinol in the perfusate in RBP-VA which may be rapidly converted to RBP-VA-PA in the blood. No effect of the thyroid hormone on uptake and release of A was observed. These data indicated that retinyl palmitate stimulates secretion of RBP-A from the liver. On the other hand, it was shown that ethanol had releasing effect of retinol from perfused liver in normal rats and this phenomena might suggest one of the mechanisms that a low level of vitamin A in the liver of alcoholism rats.
