Methods for measuring rates of synthesis of albumin by the isolated perfused rat liver

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Abstract
The rate of synthesis of albumin by the isolated perfused rat liver was calculated from estimates of the free [C14] lysine specific activities in the plasma. Livers were perfused both with rat blood and with human blood. Newly synthesized albumin was isolated from the latter experiments by means of an antiserum. Liver-donor rats were previously injected with I131-labeled rat albumin to allow measurement of the amount of rat albumin transferred to the perfusion circuit with the liver. In perfusions with human blood the average rate of synthesis of albumin, measured by direct isolation, was 12.9 mg/hr. for a liver from a 300 g rat. By an indirect method of calculation, based on the specific radioactivity of isolated albumin and the total radioactivity incorporated into plasma protein, it was 11 mg/hr. In perfusions with rat or human blood the average rate of synthesis of albumin, calculated from the amounts of [Cl4]-lysine incorporated into plasma protein and the specific activities of free lysine in the plasma, was 5 mg/hr. The possibility is discussed that the difference is due to the fact that the specific activity of lysine at the site of synthesis was less than that in the plasma. A non-protein C14-labeled basic substance other than lysine accumulated during these perfusions.