We have examined whether the amount of cellular retinal-binding protein in human liver is related to the amount of vitamin A stored in the liver. Levels of vitamin A, a~ retino1 and retinol esters, and of cellular reti.ol-binding protein have been determined in liver
8.118B18. from 6 normal adults and 11 children with
MliuJl atreaia, with and without vitamin
The level of cellular retinol-binding protein in the liver wm not related to the liver vitamin A concentration exarmned * over a 300-fold range of vitamin A levels. A h , billprs a t r d did not appear to interfere with of vitamin A, and the level of cellular retinolbipdiesl protein was comparable to that observed in the liver of normal adults. The demonstration of proper vitamin A etorsQe in treated children iaa well as normal lev& of eellalor mtinol-binding protein mggest the vitamin A deficiency frequently observed in children with WtlVJr a t & m a y be due primarily to faulty abeerption rather than a combination of poor abaorption and imp.ired hepatic vitamin A metabolism.
The liver plays a central role in the distribution and storage of vitamin A in the body (1). The liver receives newly ingested vitamin A as esters of retinol when chylomicron remnants are removed from the blood. The retinol is then either re-released to the blood, bound to the p h a protein, retinol-binding protein, which is s y n t h i m d in the liver or assigned to storage as ester. In the liver, retinyl esters are stored in the parenchymal cells and in the fat-storing cells ( 1 ).
Human liver contains relatively large amounts of cellular retinol-binding protein (CRBP) (2,3). This protein may play an important role in the cellular movements of retinol. In rat, it has been demonstrated immunohistochemically in the liver parenchymal cells and in the fatstoring cells (4-6). There appears to be considerable movement of vitamin A between these cells in the rat (7-9). The cellular location of CRBP observed in retina, testis and kidney, as well as in liver, suggests that CRBP serves in the intracellular movement of retinol during storage or transport (4-7,lO-12). In addition, CRBP has