The sensitivity and heterogeneity of histochemical markers for altered foci involved in liver carcinogenesis.

Subcutaneous injection of iron dextran resulted in a hepatic siderosis within 2 weeks in rats, as previously reported for mice. Hepatic carcinomas as well as neoplastic nodules in rats were entirely or mainly free of stainable iron and, thus, could be readily identified histologically. In addition, early carcinogen-induced altered foci were resistant to iron accumulation. In rats fed 0.02% N-2-fluorenylacetamide (FAA) for 13 weeks, the number of iron-resistant foci identified following iron injection was the same as that observed with dietary iron overload. Histochemical investigation of enzymatic markers that have been used to identify foci in rats revealed that foci characterized by enzymatic reactions of positive gamma-glutamyl transpeptidase and decreased adenosine triphosphatase and glucose-6-phosphatase corresponded to those characterized by resistance to iron accumulation. However, in quantitative analysis of the early carcinogen-induced foci in rats given iron dextran following a diet containing 0.02% 2-FAA for 13 weeks, more lesions were detected by resistance to iron accumulation than by any of these other properties. There was considerable phenotypic heterogeneity among foci for the enzyme markers. It is concluded that resistance to iron accumulation is a more sensitive and reliable marker for early carcinogen-induced altered hepatocellular foci than is any other histochemical property.