In vitro inhibition of tritiated thymidine uptake in Morris hepatoma cells by normal rat liver extract: a possible liver chalone.

A phosphate-buffered saline extract of normal rat liver tissue almost completely inhibited DNA synthesis in Buffalo rat Morris hepatoma 7777 cells in vitro. This effect was tissue-specific because it did not occur with extracts of kidney, spleen, heart, lung, muscle, and hepatoma. The liver extracts did not inhibit in vitro human prostate carcinoma or phytohemagglutinin-stimulated human and rat peripheral blood lymphocyte cultures. The addition of 10% fetal calf serum in the incubation medium had no effect on this inhibition. We determined that doses of liver extract that inhibit thymidine incorporation were not toxic inasmuch as treated cells remained viable, as indicated by trypan blue exclusion. The liver extract may thus contain a cell-specific mitotic inhibitor, a chalone for hepatoma cells.