Role of the Stability of Ribonucleic Acid Template During Induced Liver Growth

hepatomegaly (Nievel, 1969). The animals were killed 18h after the last dose of phenobarbitone. The rate of protein synthesis was assessed in uivo in dual-labelled experiments with [3H]and [14C]-leucine as precursors. Liver subcellular fractions were obtained by zonal and isopycnic ultracentrifugation. Various plasma and liver proteins, fibrinogen and plasminogen were fractionated and purified by molecular sieving and affinity chromatography. In the growing liver induced by non-toxic compounds, i.e. the food additive butylated hydroxytoluene or phenobarbitone, the synthesis of most of the liver proteins was found to be increased. An increased rate of amino acid incorporation into fibrinogen, albumin, and into some other protein fractions eluted from a Sephadex G-200 column was also detected. However, the incorporation of leucine into plasminogen in phenobarbitoneinduced hepatomegaly was significantly decreased. This effect was also observed when the incorporation of labelled leucine into plasminogen was related to the radioactivity of the free leucine-precursor pool in the plasma. The fact that plasminogen synthesis is depressed in hepatomegaly may indicate that in contrast with fibrinogen the synthesis of plasminogen, the other essential component of the fibrinolysis system, is not stimulated during induced liver growth. On the other hand the present results may also suggest that plasminogen is synthesized, in rat, outside of the liver.