Multiparameter flow cytometric analysis of hepatic nuclear RNA and DNA of normal and hepatotoxin-treated mice.

Combined immunohistologic and flow cytometric methods were used to monitor the regenerative response of the mouse liver following intraperitoneal administration of the hepatonecrotic agent carbon tetrachloride (CCl4). A slight increase in the percentage of liver nuclei engaged in DNA synthesis (S-phase population) was evident 1 day after CCl4. The percentage of S-phase nuclei increased thereafter, lasting until day 6 after CCl4 with a peak at day 2 after CCl4. The method of sampling used (every 24 hours) places the period of maximal DNA synthetic activity between 48 hours and 72 hours after inoculation of the hepatonecrotic agent; at 48 hours the number of S-phase nuclei was approximately five times higher than the nonregenerating liver. Modified multiparametric flow cytofluorimetric analysis of hepatic nuclei indicated that early repopulation of the liver in response to CCl4-induced necrosis involved the selective proliferation of a specific subpopulation of liver cells which contained diploid nuclei of high RNA content. These nuclei were also observed in control animals, suggesting the existence of a subcompartment of 2C DNA content G1 hepatocytes potentially programmed for replacement proliferation.