By applying a unique combination of enzyme histochemistry and radioautography, we investigated sequential changes of areas of hyperplasia in the liver of rats fed with diet containing 0.03% N-2-fluorenylacetamide.
In the 9th week, the areas of hyperplasia showed marked deficiency of β-glucuronidase, glucose 6-phosphatase, and canalicular adenosine triphosphatase and were selectively and intensely labeled, 18 to 27 hr after two-thirds hepatectomy, by the repeated injection of tritiated thymidine, 400 µCi/rat in total.
In the successive combined histochemical and radioautographic studies, most of the labeled areas of hyperplasia became comparable to the normal adult liver both in the enzyme level and localization within 9 weeks after labeling. Thus the regenerative character of most of these areas was impressed.
On the other hand, minor areas of hyperplasia remained deficient of the enzymes or there was slight, unusual intracellular localization of enzyme activity. These enzymedeficient areas increased in size during the observation period and were considered most significant as precancerous lesions. However, no labeled cells have been observed radioautographically in overt carcinomas, even in the earliest microscopical ones. Further modification of this method of investigation is necessary to determine the precancerous nature of these persistently enzyme-deficient areas of hyperplasia.
This work was supported in part by Grants for Scientific Research from the Ministry of Education and the Ministry of Health and Welfare, Japan.