Repeated partial hepatectomy as a promoting stimulus for carcinogenic response of liver to nitrosamines in rats.

Partial hepatectomy 24 h before a single i.p. dose of dimethylnitrosamine, diethylnitrosamine or ethylmethylnitrosamine increased the carcinogenic response in the liver of rats as determined by the number of tumours and the number of "focal proliferations" produced. Secondly, in rats given a single i.p. dose of diethylnitrosamine, 3 partial hepatectomies 5, 10 and 15 weeks after dosing the animals increased the carcinogenic response in the liver. The stimulus of repeated partial hepatectomy therefore appears to act as a "promoting agent" for liver carcinogenesis, that is if the single dose of diethylnitrosamine is regarded as an "initiating agent" in the terms of the two-stage hypothesis.