Experimental Hepatocarcinogenesis in Rat and Cellular Detection of Alpha1‐fetoprotein by Use of Peroxidase Conjugates

Hepatomas were induced in rats by feeding low doses (6 mg/kg) or high doses (20 mg/kg) of N‐nitrosomorpholine (NNM) for 12 and 6 weeks respectively. Necroses of adult hepatocytes and proliferation of oval‐shaped cells occurred only at high doses of NNM. In parallel, early reappearance of alpha1‐fetoprotein (AFP) in sera was observed in rats which were fed high doses of NNM. At this time, AFP was detected in oval‐shaped cells by means of immunoperoxidase staining techniques. Both NNM feeding schedules (low and high doses) resulted in development of hepatomas. At this stage of hepatocarcinogenesis, AFP staining nodules were seen concomitantly with non AFP staining nodules in the same animal. AFP staining cells were populations of distinct neoplastic hepatocytes with a certain degree of retrodifferentiation. Pulse‐chase experiments have shown the highly proliferative character of carcinoma cells from which the AFP staining population was the most proliferating one.