Kinetic analysis of the preserved rat liver by isolated perfusion with ammonium chloride as a load

Oxygen consumption and urea synthesis from ammonium chloride (NH4Cl) were investigated in the liver preserved in University of Wisconsin solution at 4 degrees C for 24 hours using an isolated rat liver perfusion system in which the perfusate contained five different concentrations of NH4Cl. When a Michaelis-Menten equation was applied to oxygen consumption and urea synthesis against NH4Cl concentration, the preserved liver showed smaller increase in oxygen consumption rate and larger Km of urea synthesis for NH4Cl than the fresh liver. The ratio of respiration velocity without any substrate to maximal velocity (v/Vmax), which reflects the mitochondrial functional reserve, was 55.9 +/- 4.1% and 41.5 +/- 4.8% in the preserved and fresh liver, respectively (p less than 0.05). From the viewpoint of work-cost relationship, it was shown that the mitochondrial function in the preserved liver was deteriorated. On the other hand, conventional mitochondrial study after rewarming and reoxygenation but before NH4Cl load revealed no deterioration of mitochondrial function after preservation. These results indicate that it is necessary to take the metabolic load on the reperfused liver into account when assessing graft viability, and that high v/Vmax suggests decrease in the reserve of mitochondrial function under consideration of the metabolic load.