Evaluation of an in vitro method for the study of hepatic protein synthesis in liver ischemia

The effects of liver ischemia on hepatic protein synthesis were studied by measuring the incorporation of radioactivity into protein in rat liver slices incubated in a medium containing 14C-leucine and a mixture of 19 L-amino acids at a concentration four times that in plasma. Following liver ischemia for 1 h the amount of radioactivity incorporated into protein was reduced by about 60%. Specific radioactivity of free 14C-leucine in incubation medium and incubated liver slices was not different when slices from control or ischemic liver were incubated. Thus, apparent reduction of leucine incorporation into protein in ischemic liver slices probably reflected decreased protein synthesis and not reduction of precursor specific radioactivity. Changes of in vitro protein synthesis in the postischemic liver (1 h following reperfusion) were compared to changes in vivo. Protein synthesis in vivo was determined from specific radioactivity of protein-bound and free 14C-leucine in liver tissue following intravenous administration of a large dose of 14C-leucine. Protein synthesis in vivo was reduced to 30% of the control value in the postischemic liver. The corresponding value in vitro was 40%. Alterations of protein synthesis in vitro during and after a period of liver ischemia were similar to changes of ATP in liver tissue. Thus, changes of protein synthesis noticed in vitro reflected alterations of protein synthesis in vivo and changes of energy level in liver tissue. The results indicate that the present in vitro system is suitable for studying the effects of ischemia on hepatic protein synthesis.