Nonlinearity of nuclear enlargement in hepatocytes induced by the carcinogen N '-nitrosomorpholine in ovo

In this study we investigated the effects of different doses of the carcino genic nitrosamine N'-nitrosomorpholine (NNM) on the occurrence of enlarged nuclei in embryonic turkey liver in order to evaluate whether this paramete r might represent a quantitative indicator of chemically induced hepatocarc inogenesis. Therefore fertile embryo turkey eggs were injected with NNM ove r a dose range of 125 mu g-8 mg/egg at the first day of incubation. After i ncubation for 24 days, the embryonic livers were removed and processed for histologic evaluation. The induction of hepatocytes with enlarged nuclei (n uclear profiles > 35 mu m(2)) was quantitated morphometrically in hematoxyl in and eosin (H&E)-stained sections. The NNM treatment increased both the n umber of enlarged hepatocyte nuclei and the areas of the individual profile s of the enlarged nuclei in a dose-dependent manner. Exposure to 500 mu g-8 mg NNM/egg resulted in a statistically significant increase in the number of hepatocytes with enlarged nuclei. The lower doses of 250 mu g and 125 mu g NNM/egg showed a similar albeit not significant trend. Signs for cytotox ic effects on the hepatocytes, such as necrosis or enhanced cytoplasmic vac uolization, were observed in tissue samples of embryos exposed to 4 or 8 mg NNM, but not after treatment with lower doses. The dose-effect curve for t he induction of the nuclear enlargement was nonlinear, with a moderate slop e for lower dose levels of 125-500 mu g/egg and a steep slope for higher do se levels of 1-8 mg. Findings in rodents indicate a pathogenic link between the occurrence of enlarged nuclei and hepatocarcinogenesis. Based on the r esults with NNM, it is suggested that the in ovo model may represent a rapi d, convenient, and inexpensive experimental approach for dose effect invest igations on chemically induced hepatocarcinogenesis.