Carcinogens/toxicity; Electrophoresis, Gel, Two-Dimensional; Gene Expression Profiling; Gene Expression Regulation, Neoplastic/genetics; Inactivation, Metabolic/genetics; Liver Neoplasms, Experimental/chemistry; Neoplasm Proteins/analysis; Proteome; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Aldehyde Reductase/analysis; Aldehyde Reductase/chemistry; Aldehyde Reductase/genetics; Aldo-Keto Reductases; Amino Acid Sequence; Animals; Base Sequence; Carcinogens/pharmacology; Diethylnitrosamine/pharmacology; Diethylnitrosamine/toxicity; Fetal Proteins/analysis; Fetal Proteins/genetics; Isoenzymes/analysis; Isoenzymes/genetics; Liver Neoplasms, Experimental/chemically induced; Liver Neoplasms, Experimental/genetics; Liver Neoplasms, Experimental/metabolism; Male; Methylnitrosourea/pharmacology; Methylnitrosourea/toxicity; Molecular Sequence Data; Nafenopin/pharmacology; Nafenopin/toxicity; Neoplasm Proteins/biosynthesis; Neoplasm Proteins/genetics; Nitrosamines/pharmacology; Nitrosamines/toxicity; Organ Specificity; Peroxisome Proliferators/pharmacology; Peroxisome Proliferators/toxicity; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; Sequence Alignment; Sequence Homology, Amino Acid; Subtraction Technique