Susceptible and resistant subgroups in genetically identical populations: response of mouse liver neoplasia and body weight to phenobarbital

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Abstract
Following 17 – 19 months of feeding 500 p.p.m. sodium phenobarbital (PB) in the diet to yellow Avy/A and agouti A/a (C3H x VY) F1 hybrid male mice, two subgroups differing in responsiveness to PB with respect to promotion of hepato-cellular adenomas and body weight gain were observed within each genotype. In untreated mice of both genotypes, the presence of an adenoma at necropsy was associated with decreased body weight gain during this study. However, PB treatment inverted this association. In treated mice the presence of an adenoma at necropsy was preceded by a greater increase in body weight during the study than when no tumor was present. This increase in average body weight gain was more pronounced among the yellow mice (44%) than among the agouti mice (21%). Among yellow mice PB treatment had no effect on body weight gain unless an adenoma was present at necropsy. However, in those yellow mice in which an adenoma was found, body weight was greater than in untreated yellow controls throughout the study beginning at week 27. The mean body weight curve of treated yellow mice bearing one adenoma was slightly higher than that of treated yellow mice in which no adenoma was found. The mean body weight curve of treated yellow mice bearing multiple adenomas was significantly higher than those of yellow mice with no or only one adenoma.