The early effects of chemical carcinogens on adult rat hepatocytes in primary culture: I. Quantitative changes in intracellular enzyme activities following a single dose of carcinogen

The effects of exposure of adult rat hepatocytes to chemical carcinogens have been studied using a short-term maintenance culture system. Scanning microdensitometry was used to quantitate the observed changes in enzyme activity. The dose-response curves showed a biphasic response for all 4 enzymes studied (glucose-6-phosphate dehydrogenase, succinate dehydrogenase, NADPH oxidase and gamma-glutamyl transpeptidase) there being decreased enzyme activities at the higher dose levels used, possibly indicating cytotoxicity. The enhancement of enzyme activity at low dose levels was due to generalised increases occurring in every cell, rather than to selection of a cell species particularly high in enzyme activity. A culture period of 24 h was necessary for the complete adaptation of the cells to the culture environment as evidenced by the response of intracellular glucose-6-phosphate dehydrogenase activity to carcinogen treatment. These findings are discussed in relation to previously reported in vivo studies.