Human hepatocyte growth factor in plasma from patients with fulminant hepatic failure

Effect of histamine H2-receptor antagonists on DNA synthesis in adult rat hepatocytes in primary culture. Cimetidine enhanced hepatocytes proliferation stimulated with insulin and epidermal growth factor

The effects of three of the most widely used histamine H2-receptor antagonists, cimetidine, ranitidine and famotidine, on liver cell growth were studied in vitro using adult rat hepatocytes in primary culture, because these antagonists are commonly given to patients with hepatic cirrhosis or fulminant hepatic failure for protection against peptic ulcers and gastrointestinal hemorrhage. At their clinically effective concentrations in the blood (0.5-5 micrograms/ml cimetidine, 0.25-2.5 micrograms/ml ranitidine and 0.05-0.5 microgram/ml famotidine), these three antagonists did not have any effect on replicative DNA synthesis either in the presence or absence of insulin plus epidermal growth factor (EGF). However, unexpectedly DNA synthesis stimulated by insulin and EGF was found to be enhanced by 0.05-0.5 mg/ml cimetidine, although it was unaffected or inhibited by ranitidine and famotidine at the concentrations tested. Cimetidine caused maximal enhancement of 1.5-2 times the control level of DNA synthesis at a concentration of 0.25 mg/ml. Cimetidine also had an enhancing effect at submaximal concentrations of insulin and EGF, but neither cimetidine nor the other antagonists had any stimulatory effect on DNA synthesis in the absence of insulin plus EGF. This enhancement of DNA synthesis by cimetidine resulted in significant increase in the total DNA content of the hepatocytes in culture. Under the conditions used, cimetidine had the lowest toxicity of these three antagonists and ranitidine the highest, as judged from data on DNA synthesis and the total protein content of cultured hepatocytes, leakage of aminotransferases from the cells and morphological observations.

Mechanisms of rodent liver carcinogenesis

Stimulation of DNA synthesis by peroxisome proliferators, including DEHP, should be viewed differently from the stimulation of DNA synthesis by xenobiotic chemicals which stimulate restorative hyperplasia after hepatic necrosis induced by the toxicity of the chemical. The emerging picture of the control mechanisms for hepatocyte proliferation suggests that rather few and distinct factors are involved. The stimulation of DNA synthesis by peroxisome proliferators should be examined in the context of the effects of these factors. Comparisons with other xenobiotics show that induction of DNA synthesis at rates comparable to those of peroxisome proliferators is not sufficient to explain the rates of carcinogenicity associated with peroxisome proliferators. These considerations lead to the conclusion that although DNA synthesis enhances the incidence of neoplasia, it should not be viewed as a complete carcinogen, nor should it be considered as resulting in initiation at rates that can explain the carcinogenic potency of compounds such as peroxisome proliferators.