Retinol and retinyl esters in rabbit bone marrow and blood leukocytes

Due to the well documented effects of retinoids on growth and differentiation of some leukaemic cells in vivo and in vitro, we measured the amount of retinol and retinyl esters in bone marrow, blood leukocytes, and liver in rabbits fed large doses of retinyl palmitate. Both Chinchilla rabbits and Watanabe Heritable Hyperlipidaemic rabbits which lack functional low density lipoprotein receptors, were fed 26 mumoles (25.000 IU) of retinyl palmitate daily for 8 weeks. The animals stored retinoids in large amounts in the liver, whereas only minor amounts were stored in bone marrow. More than 97% of the retinoids in the liver was esterified, while most of the retinoids in bone marrow were unesterified. We also studied the post-prandial increase in chylomicron associated retinyl esters in rabbit leukocytes in vivo. After administering an oral load of 26 mumoles retinyl palmitate, retinoids increased four-fold in blood leukocytes after 5 h. There was almost no difference in retinoid uptake in leukocytes in Watanabe Heritable Hyperlipidaemic rabbits compared to normal rabbits, suggesting that chylomicron remnant retinyl esters are taken up in peripheral blood leukocytes independently of the low density lipoprotein receptor. In conclusion, bone marrow does not store high amounts of retinoids, and retinyl ester transport and storage appear normal in absence of functional low density lipoprotein receptors.