Increased incorporation of 3H-thymidine into rat liver DNA after handling of liver lobes.

Handling of part of the rat liver without resection or interference with the vascular supply was associated with an increased rate of incorporation of H-thymidine into DNA. The response curve was distinctive and different in shape and in magnitude from that which occurs after partial hepatectomy. Incorporation was greater in the peripheral rather than central parts of the liver, was more striking after i.p. rather than intravenous administration of isotope and was associated with a proliferation of hepatic capsular cells. Radioautographs showed activity in capsular cells, inflammatory cells and also in a few peripherally placed hepatocytes. The possibility is canvassed that this phenomenon may have led to misinterpretation of results of experiments designed to test for the presence of humoral stimuli or inhibitors in restoration of the liver.