Unscheduled DNA synthesis was induced by procarcinogens in freshly isolated suspensions and primary cultures (6 days old) of hepatocytes on collagen membranes. Incorporation of [3H]thymidine in the presence of hydroxyurea was used to measure unscheduled DNA synthesis. When hepatocellular DNA was isolated on cesium chloride gradients, significant levels of unscheduled DNA synthesis were measured. Similar concentrations of procarcinogens elicited higher levels of unscheduled DNA synthesis in hepatocellular suspensions than in primary cultures. The results demonstrate that hepatocytes cultured on collagen membranes can metabolize chemical carcinogens. Suspensions of freshly isolated hepatocytes, however, are more active in procarcinogen metabolism than are those of primary cultures. The selective advantages of the two systems of hepatocytes can be utilized for the establishment of short-term in vitro screening systems of mutagens and carcinogens.
The work reported in this paper was supported in part by Grant CA-07175 from the National Cancer Institute.