Abstract
Morphology and incidence of altered hepatocellular foci (AHF) were evaluated in standard H&E-stained liver sections from 3 groups of control Sprague-Dawley (SD) rats (initially 70/sex/group) used in 2 2-yr carcinogenicity studies. All AHF observed could be classified as basophilic, eosinophilic, clear, vacuolated, or mixed types using criteria applied previously to the Fischer-344 (F-344) rat. Some eosinophilic foci were large and posed a diagnostic challenge in differentiation from hepatocellular adenoma. Rats were arbitrarily divided into 3 classes by age at death: 14-17, 18-23, and 24-26 mo. As reported for F-344 rats, the incidence of SD rats with AHF increased with age, and males with eosinophilic foci predominated over males with basophilic foci whereas the opposite held true for females. Mean incidence of rats with AHF at 18-23 mo was 28 and 38% for males and females, respectively, and at 24-26 months was 68 and 71%, respectively. These data indicate a strikingly lower incidence of spontaneous AHF in SD rats than that reported for F-344 rats.