The Secretion of Serum Protein and the Synthesis of Albumin and Total Protein in Regenerating Rat Liver

The regulation of albumin synthesis and serum protein secretion was studied in regenerating rat liver by measuring incorporation of 14C-leucine. Albumin was isolated to radiochemical purity, utilizing a method which eliminates the influence of precursor pool changes on protein labeling. Changes in the size of the product pool were measured. The following results were obtained. 1. The time period between intracaval injection of 14Cleucine and the appearance of radioactive protein in the blood (secretion time) decreased from 15 min for normal animals to a minimum of 10 min at 48 hours after removal of 70% of the liver. 2. At 10 min after intracaval injection of 14C-leucine, 3.5% of total protein radioactivity was found in albumin in normal liver, whereas in regenerating liver only 1.4% of the total protein radioactivity was incorporated into albumin. 3. Albumin concentration in the serum decreased from 29.2 mg of albumin per ml of serum for normal rats to a minimum of 17.3 mg of albumin per ml of serum at 4 days after partial hepatectomy. 4. The half-life of albumin was 2.66 days for normal rats and 2.13 days for animals, 48 hours after partial hepatectomy. 5. The intravascular pool of albumin decreased from 100 mg of albumin per 100 g, body wt, in normal rats to 57.8 mg of albumin per 100 g, body wt, in partially hepatectomized animals, 48 hours after operation. The extravascular and the total body pool of albumin also decreased after partial hepatectomy to a minimum at 24 hours after the operation. In contrast to the intravascular pool, the extravascular and the total body pool increased again, reaching a plateau between 2 and 4 days after the operation. 6. During regeneration, the proportion of leucine to other amino acids in total liver protein did not change. Also, this proportion did not differ significantly from that found in serum albumin. 7. The net rate of albumin synthesis changed only slightly from 20.1 mg of albumin per day per g of liver for normal to 23.9 mg albumin per day per g of liver for regenerating liver 48 hours after partial hepatectomy. In contrast, the net rate of synthesis of total liver protein increased from 576 mg protein per day per g of liver in normal rats to 1710 mg of protein per day per g of liver in rats 48 hours after partial hepatectomy.