The Concentration and Temporal Relationships of Acetaminophen‐Induced Changes in Intracellular and Extracellular Total Glutathione in Freshly Isolated Hepatocytes from Untreated and 3‐Methylcholanthrene Pretreated Sprague‐Dawley and Fischer Rats*

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Abstract
Fischer rats are more sensitive to acetaminophen‐induced hepatotoxicity than Sprague‐Dawley rats, however, the mechanisms for this enhanced sensitivity remain unclear. The susceptability to hepatotoxicity is determined largely by the balance between acetaminophen toxification and detoxification. Since glutathione plays a critical role in the detoxification process, it would be of interest to compare the effects of acetaminophen on hepatic glutathione homeostasis in the Sprague‐Dawley and Fischer rat, and relate these effects to cytotoxicity. To this end, we measured the sequential changes of intracellular and extracellular total glutathione in freshly isolated hepatocytes from untreated and 3‐methylchol‐anthrene pretreated Fischer and Sprague‐Dawley rats, both in the absence (basal) and presence of acetaminophen. In the basal state, the intracellular total glutathione content was significantly (P < 0.01) increased in hepatocytes from untreated Fischer rats. Nevertheless, the sequential release of total glutathione into the medium and the sequential depletion of intracellular total glutathione were quantitatively similar in hepatocytes from untreated Fischer and Sprague‐Dawley rats. Following exposure to acetaminophen, there was a striking dose and time associated depletion of intracellular total glutathione in untreated hepatocytes from both rat strains, and quantitatively the depletion was similar in untreated hepatocytes from both rat strains. This degree of depletion of intracellular total glutathione was not associated with acetaminophen‐induced cytotoxicity in Sprague‐Dawley hepatocytes, whereas significant (P < 0.05) cytotoxicity was demonstrated in Fischer hepatocytes. In hepatocytes from 3‐methylcholanthrene pretreated rats, there was an even more marked dose and time associated depletion of intracellular total glutathione as compared with untreated hepatocytes from both rat strains. Although the magnitude of this depletion was also similar in hepatocytes from both rat strains, the acetaminophen‐induced cytotoxicity was significantly (P < 0.01) more prominent in hepatocytes from the Fischer rat. Our observations establish that basal hepatocellular glutathione concentrations are higher in Fischer than Sprague‐Dawley rats, however sequential changes in basal intracellular and extracellular glutathione are similar in hepatocytes of both strains. Moreover, the effect of acetaminophen on these glutathione measures was also similar in hepatocytes from both rat strains. Finally, our observations reveal a discordance between acetaminophen‐induced cytotoxicity and cellular glutathione content in the two rat strains, implying that the Fischer rats'enhanced susceptibility to hepatocellular injury may be related to a defective inherent cellular defense mechanism against attack by the reactive metabolite of acetaminophen.
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