Intracellular lactate dehydrogenase concentration as an index of cytotoxicity in rat hepatocyte primary culture.

In searching for a reliable index for cytotoxicity testing in rat hepatocyte primary culture, lactate dehydrogenase (LDH) concentrations in lysates of attached hepatocytes and LDH released into the culture medium were compared under conditions of exposure to various dosages of sodium chloride, sodium salicylate, R-warfarin, acetaminophen, phenylbutazone, and furosemide (frusemide). The amount of intracellular LDH was assessed by inducing the cells to release the enzyme with 0.1% Triton X-100. The induced LDH leakage was completed in 1 hr and the LDH activity was stable in storage at 10 degrees for 2 weeks. We found that intracellular LDH is a direct indicator of the number of viable hepatocytes in contrast to the LDH released, because released LDH does not account for the significant number of cells detached from monolayer but which are not leaky, during the 6-hr test period. Based on IC50 values (50% inhibitory concentration), the relative cytotoxicities are R-warfarin greater than phenylbutazone greater than furosemide greater than acetaminophen greater than sodium salicylate greater than sodium chloride.