Synthesis and secretion of rat albumin in vivo, in perfused liver, and in isolated hepatocytes. Effects of hypophysectomy and growth hormone treatment.

The effects of hypophysectomy on albumin and total protein synthesis in rat liver were investigated in vivo, in perfused liver, and in isolated hepatocytes. In all systems, hypophysectomy resulted in about a 50% decrease in the rate of total protein synthesis and a 30 to 50% decrease in the relative rate of albumin synthesis. Albumin synthesis accounted for 11 to 13% of total protein synthesis in all normal systems, but represented only 5 to 8% of the total in all systems derived from hypophysectomized rats. Growth hormone, administered subcutaneously to hypophysectomized rats for 5 days, restored the relative rate of albumin synthesis to normal in vivo; however, only partial restoration was demonstrated in the in vitro systems. Perfused livers and isolated hepatocytes exhibited linear rates of total protein and albumin secretion for 3 h. The rate of albumin secretion by normal perfused livers was 3 times that of perfused livers from hypophysectomized animals, being 0.54 and 0.17 mg/g of liver/h, respectively. Isolated hepatocytes synthesized total protein and albumin at nearly the same rate as perfused livers. The amount of albumin secreted by cells derived from normal and hypophysectomized rats was 0.38 and 0.10 mg/ml of packed cells/h, respectively. Ribosome half-transit times for albumin and total liver protein were 1.6 to 1.7 min in isolated liver cells derived from both normal and hypophysectomized rats. Analysis by polyacrylamide gel electrophoresis showed no difference in the qualitative distribution of the proteins secreted by perfused livers and isolated hepatocytes.