Albumin synthesis by the perfused rat liver. A comparison of methods with special reference to the effect of dietary protein deprivation

1. Isolated perfused rat livers were used to study synthesis of albumin after donors had been fed on normal or protein-free diets. 2. Methods of determining the liver's ability to produce albumin included incorporation of [¹⁴C]carbonate, [³H]lysine and [¹⁴C]arginine, as well as a direct method based on a heterologous perfusing system of rat erythrocytes and rabbit plasma. 3. Livers from protein-deprived rats were found to form extremely little urea and not to incorporate ¹⁴CO₂ into [¹⁴C]urea, but they were capable of producing [¹⁴C]urea from [¹⁴C]arginine and of incorporating the latter and [³H]lysine into albumin. 4. By immunological means these lives were found to synthesize less albumin than normal, but their ability was only slightly impaired when related to body weight or liver weight. 5. These findings are consistent with a block in urea-cycle enzymes with relative integrity of arginase activity and of amino acid activation.