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Influence of Actinomycin D and Puromycin on Net Synthesis of Plasma Albumin and Fibrinogen by the Isolated Perfused Rat Liver

From the ¹ From the Department of Radiation Biology and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14620

Rat livers were perfused 6 hours with defibrinated rabbit blood with dl-lysine-1-¹⁴C and 250 mg of glucose infused for the first 4 hours. Net changes in rat albumin and fibrinogen in perfusate plasma were measured serologically. Fibrinogen was also measured chemically by clotting with thrombin.

Puromycin (15 mg at outset plus 15 mg infused) stopped virtually all ¹⁴C incorporation into plasma and hepatic proteins after 30 min; net rat serum albumin and fibrinogen increased until 2 hours, indicating release of preformed plasma proteins from the liver. Average synthesis rates (milligrams per g of liver per hour) in control perfusions, estimated from net increases above those in puromycin perfusions, were: 0.47 ± 0.05 for rat serum albumin; 0.58 ± 0.15 for fibrinogen, measured serologically; and 0.64 ± 0.20 for fibrinogen, measured chemically.

Actinomycin D (117 µg at outset plus 117 µg infused) was added to perfusions of livers from normal rats and from rats that had been injected intraperitoneally with actinomycin D (150 µg/100 g) 3 hours before perfusion. Decreases in protein synthesis rates after treatment with actinomycin D were interpreted as secondary to decay of messenger ribonucleic acid following inhibition of its synthesis, allowing the following estimates of average messenger ribonucleic acid half-life: rat serum albumin, 2 to 4 hours; fibrinogen, 1 to 2 hours; plasma proteins synthesized by the liver other than rat serum albumin and fibrinogen, 3 to 4 hours; and hepatic proteins, less than 6 hours.

Net changes in urea, glucose, and -amino acids in perfusate were similar in actinomycin D and control perfusions, but were elevated in puromycin perfusions. In comparison with control perfusions, both inhibitors caused similar increases in the rate of oxidation of l-lysine-1-¹⁴C to ¹⁴CO₂.

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