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Evaluations of the toxic potential of drugs and chemicals often involve statistical comparisons of effects between treatment groups. Such comparisons are valid and permit elucidation of spontaneous versus treatment effects only if the sampling population is obtained without selection bias. Selection bias is routinely minimized or controlled by random sampling or unbiased allocation of animals to treatment groups. A systematic approach using a computerized procedure is described that fulfills these requirements in a simple and efficient fashion.

The carcinogenic potential of tilidine fumarate, a synthetic analgesic, was studied for 80 and 104 weeks in mice and rats, respectively. Groups of 50 albino CF1 mice and 65 albino Wistar rats of each sex received tilidine fumarate-lactose blend (1:1) at doses of 100, 40 and 16 mg/kg. The control groups consisted of 100 mice and 115 rats of each sex and received the lactose vehicle only. Treatment-related non-neoplastic changes consisted of reversible, increased cytoplasmic eosinophilia of hepatocytes in high and mid dose rats corresponding to areas of proliferating smooth endoplasmic reticulum; and an increased incidence in high dose rats of proliferative or cystic lesions of the biliary epithelium. Adequate survival rates allowed stringent statistical analysis of neoplasia. Tilidine did not evoke increased tumor incidences or changes in the average latency or onset of tumors in either species. The most frequent tumors represented spontaneous neoplasia characteristic of historical background incidence in these strains. In mice, the only statistically significant (P less than 0.01) variation in tumor incidence was an increased rate of lung alveologenic adenocarcinomas in females at 100 mg/kg (24%), compared with the concurrent untreated controls (10%), but without a statistically significant difference from historical control data (27%). Female rats given 100 mg/kg showed statistically significant (P less than 0.01) decreased incidences of mammary fibroadenoma and pituitary adenoma. From these data, it was concluded that the synthetic analgesic tilidine does not possess tumorigenic potential in rodents.

Environmental pollutants, Aroclor-1254 (PCB) and 3-methylcholanthrene (MC), were employed in this study to investigate some aspects of the induction of hepatic drug metabolism in rats. PCB and MC treatments increased 7-ethoxyresorufin and 7-ethoxycoumarin O-deethylase activities related to cytochrome P-448. Cytochrome P-450 reductase activity was increased by PCB while no effect was observed by MC treatment. Pretreatment with PCB resulted in approximately 50% increase in the phospholipid content of the microsomes whereas MC caused no change. Liver microsomal cholesterol content was decreased while triglycerides were increased by PCB. The ratio between saturated and unsaturated fatty acids (saturation index) decreased in the total microsomes and phospholipids with PCB treatment, whereas MC did not alter the ratio, except that the major effect of MC was observed in the acyl derivatives of microsomal phosphatidylethanolamine. It is proposed that the uniaxial rotation and mobility of hemoproteins may be restricted by an increase in the saturation index of the membrane, while a decreased index may facilitate contact with reductases for electron transfer by enhanced membrane fluidity. The decreased saturation index after treatment with MC may play a role in carcinogenicity by triggering induction of free radicals.

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