Quantification of nuclear pores in tumor promoter-induced hepatic nodules in rats: a freeze-fracture study

Twelve-week-old outbred female Sprague-Dawley rats weighing 190-210 g were partially hepatectomized and given diethylnitrosamine intraperitoneally (10 mg/kg) 24 h later. Thirty days later, rats were fed a diet containing tumor-promoting doses of two polybrominated biphenyl (PBB) congeners for 140 d. Rats were then maintained on diets free of PBBs until d 480, at which time they were killed and necropsied. Sections of liver containing hepatic nodules as well as nonnodular sections of liver were freeze-fractured and examined with transmission electron microscopy to quantify nuclear pores. Numbers of nuclear pores per square micrometer in sections of hepatic nodules were not significantly different from those in nonnodular liver. It is concluded that there are minimal quantitative differences in the numbers of nuclear pores in PBB-induced hepatic nodules when compared to nonnodular hepatic tissue from the same animal.