The long term objective of this study is to refine the infant mouse model for hepatocarcinogenesis and further characterize the microscopic hepatocellular lesions induced by single injections of carcinogens. Recent morphologic and kinetic data from my laboratory strongly suggest that single small doses of diethylnitrosamine in infant mice induce hundreds of hepatocellular foci, many of which progress to microcarcinomas and then to metastasizing trabecular hepatocellular carcinomas. Therefore there is good reason to believe that further evaluation of the model may provide the means for rapid evaluation of the relative carcinogenic, promoting and antipromoting effects of various environmental chemicals and dietary constituents. The effects of single injections of complete carcinogens (diethylnitrosamine, ethylnitrosourea, aflatoxin B1 and ethyl carbamate) and of post-initiation modifiers (caloric restriction, phenobarbital and partial hepatectomy) on foci growth kinetics will be determined. Since our new growth kinetic methods are very sensitive and permit us to estimate changes in growth rates on the basis of a comparison of size distribution and numerical densities of foci at several time points, we should be able to determine whether a particular effect is on the rate of growth of neoplasms or on changes in the number of foci that start to grow. These techniques to study growth kinetics of large populations of foci will be complemented by studies of other kinetic methods using 3H-TdR labeling indices. In another series of experiments livers will be perfused and attempts made to separate hepatocytes in foci by centrifugation and flow cytometry and to grow them in short term cultures. Light microscopic, ultrastructural and histochemical techniques, will also be used for study of the foci and their vascular invasive features under many of these different in vivo and in vitro conditions.
