Impairment of albumin synthesis in cell-free systems from rat liver

The kinetics in vivo of the synthesis of albumin-like protein and albumin in rats

The incorporation of radioactivity into total protein, albumin-like protein and albumin in liver and into total protein and albumin in blood plasma, was studied for a time period of 2 h after intraportal injection of L-[1-14C]leucine. 1. In the liver, radioactivity began to increase in albumin-like protein before 2.5 min and in albumin at about 10 min after injection. In the plasma, radioactive albumin appeared at about 15 min. No albumin-like protein could be detected in the plasma. 2. Maximum radioactivity was reached first in albumin-like protein, then in hepatic albumin and finally in albumin in the blood-stream. The maximum specific radioactivity of albumin-like protein was 15 times higher than that of extravascular hepatic albumin which, in turn, was 6 times higher than that of plasma albumin. 3. The increase of radioactivity in albumin in the blood corresponded almost quantitatively to the decrease of radioactivity in albumin-like protein. 4. It is concluded that the albumin-like protein is the precursor of albumin in vivo. It is converted into albumin 5-6 min before the appearance of newly synthesized albumin in the blood-stream.

Albumin and transferrin synthesis during development in the rat

In this study, the incorporation of [(14)C]leucine into albumin and transferrin in early rat foetuses, vitelline plus amniotic membranes, chorioallantoic placenta and perinatal rat liver slices was measured and used to detect and compare the rates of synthesis of the two proteins. Albumin synthesis was detected in the body of foetuses from 13 days gestation onwards. Transferrin synthesis was detected only after day 15. Transferrin synthesis was demonstrable in the membranes but not in the chorioallantoic placenta of all the animals investigated, i.e. from 13 to 19 days gestation. Synthesis of albumin and transferrin by the liver of near-term and postnatal animals was shown to correlate with published data on the parenchymal cell number/unit wet wt. of liver. Near-term foetuses synthesized relatively more transferrin than albumin when compared with 10-day postnatal animals. The serum concentrations of the two plasma proteins were also determined. These increased before term whereas the rate of synthesis of albumin and transferrin declined. Postnatally, plasma albumin concentration increased but transferrin concentration decreased, yet the rates of synthesis of both proteins by the liver increased with age. This lack of correlation between the rates of synthesis of the two proteins and their respective plasma concentrations could be explained in part by their increased stability after birth. There was also evidence that the liver haemopoietic cells took up transferrin although they do not synthesize the protein. Thus the decrease in this population of cells during development could also contribute to the discrepancy between liver synthesis and serum concentrations of transferrin.