Application of quantitative stereology to the evaluation of phenotypically heterogeneous enzyme-altered foci in the rat liver.

Quantitative stereologic relationships are applied in this report to the evaluation of F344 rat liver foci where the tissue sections exhibit congruent enzyme-altered areas of the several different phenotypes as well as enzyme-altered areas within a larger area of another enzyme alteration, that is, a "focus within a focus.' Quantitation of both the numbers and volume occupied by each of the phenotypes of the enzyme-altered foci was accomplished by the unique logic described in this report. The application of this logic to four representative experimental protocols with the use of three phenotypic markers demonstrated all possible congruent phenotypes as well as a small number of "foci within foci.' The variance of the quantitation of the experimental data was shown to depend on the number of focal transections identified in the sections, the number of sections examined, and the distribution of phenotypic alterations among foci.