The synthesis of plasma lipoprotein by rat liver.

The immunochemical technique, first employed in the study of albumin synthesis in chicken liver slices by Peters and Anfmsen (3), has recently been successfully used with rat liver slices by Marsh and Drabkin (4) as well as by Campbell and Stone (5). The present work extends this technique to the problem of the biosynthesis of plasma lipoprotein by rat liver. The liver has been shown to be the site of plasma cholesterol and phospholipid synthesis (6,7). Miller et al. (8) observed that the plasma proteins (exclusive of gamma globulins), were labeled when radioactive amino acids were perfused through the isolated rat liver. Indirect evidence that the liver is capable of synthesizing plasma lipoproteins has recently been obtained by Radding et al. (9) who observed the incorporation of radioactive amino acids into lipoproteins of serum that had been incubated with rat liver slices. The present experiments demonstrate by the immunochemical method a net synthesis of low density lipoproteins in rat liver slices and in the isolated liver perfused with washed red blood cell suspensions. By this means, also, a direct estimate of the rate of synthesis of the cholesterol moiety of the plasma lipoproteins has been obtained for the first time in a mammalian system in vitro.