Stability of mixed function oxidases in frozen rabbit liver.

Little information is available on the effect of storage on hepatic mixed function oxidases. Livers from male New Zealand White rabbits were excised, frozen and maintained at -74 degrees C. Assays were conducted immediately on samples of unfrozen liver (day 0) and on thawed samples of the frozen liver at days 49, 92, 142, 181, and 221. Influence of storage on microsomal protein content, aniline hydroxylase activity, cytochrome P-450, and metabolism of digitoxigenin were determined at each time point. After day 92, homogenates gradually began losing the ability to metabolize digitoxigenin to 6beta-hydroxy-3-epidigitoxigenin, with 50% of the original activity at day 221. The amount of 3-epidigitoxigenin increased after day 92 in an amount equal to the loss of formation of 6beta-hydroxy-3-epidigitoxigenin. Microsomal protein content, aniline hydroxylase activity, and cytochrome P-450 content did not significantly change over the course of 221 days.