INVIVO UPTAKE OF CHYLOMICRON (H-3)-LABELED RETINYL ESTER BY RAT-LIVER - EVIDENCE FOR RETINOL TRANSFER FROM PARENCHYMAL TO NON-PARENCHYMAL CELLS

Hepatic uptake of chylomicron retinyl ester was studied. Chylomicrons were obtained from intestinal lymph of rats that were given retinol in groundnut oil by intraduodenal injection. When lymph was injected i.v. into normal rats, the radioactivity was cleared from blood with t1/2 [half-life] .apprxeq. 10 min. Retinyl ester was taken up initially by the liver, which, after 30 min, contained 80-90% of the radioactivity injected. Initially, most of the radioactivity was in hepatocytes, but after 30 min it disappeared from these cells and reappeared in nonparenchymal liver cells. After 2 h these cells contained more radioactivity than the hepatocytes. When lymph was injected into vitamin A-deficient rats or rats given vitamin A in the form of retinoic acid, the plasma clearance and initial hepatic uptake of radioactivity were similar to that found in control animals. However, the nonparenchymal cells in these animals did not accumulate radioactivity. The current data suggest that vitamin A (in chylomicron remnants) is taken up initially by hepatocytes and then is released from these cells and delivered mainly to nonparenchymal liver cells in normal animals. In vitamin A-deficient rats, the vitamin is transferred from the hepatocytes to extrahepatic tissues.