Light microscopic computer assisted morphometry was performed with an image analysis system of the hepatocyte nuclei and intracytoplasmic vacuoles of rat liver. Nuclei in 25 fields of view were measured in stained 4 µm embedded sections. Care was taken to include representative fields from all lobular regions. These were selected at random but were included only if scanning indicated that fixation was adequate. To ascertain the relationship between the increase in liver weight of flight animals and the results of this study, an assumption was made that the specific gravity of the vacuolar contents was similar to that of the other extranuclear components of the hepatocyte.

Results:

On that basis, calculations showed that the elevated vacuolar volume density in the flight group did not cause the increased liver weight in those animals, but that the non-nuclear, non-vacuolar parenchymal compartment did contribute significantly. Since only rare vacuoles were stained in all groups, severe glycogenic infiltration was regarded as the most likely cause of the pale appearance of the flight livers. Supporting this conclusion is the fact that glycogen would have been dissolved in the aqueous fluids used in processing, leaving empty spaces such as those seen in preparations. Regardless of the correctness of these assumptions, there is little doubt that changes in nuclear and vacuolar components were only minor contributors to the increased liver weight of the flight animals, while the remainder of the hepatocytic cytoplasm contributed the major portion of the increase.