Synergistic mutagenicity of tetracycline(TC) and nitrite was investigated by the bacterial mutation test in the Salmonella/microsome system by using the reaction products obtained under neutral condition as well as under acidic condition (in simulated gastric juice). Results from tests using Salmonella typhimurium TA 100 disclosed a significant increase in the appearance of histidine (+) (his⁺) revertants by the reaction product between TC and nitrite in the presence of the rat liver-microsomal enzyme system(S9 mix), while the mutagenic potency of the reaction product of the two compounds in simulated gastric juice was extremely weak. In the process of the reaction of TC with and without nitrite in the presence of S9 mix, formaldehyde was detected, indicating the demethylation of TC by demethylase in S9. To explain the induction mechanism of the synergistic mutagenicity of TC and nitrite, it was suggested that the alkylating reaction of nitroso compound formed by nitrosation of the 4-demethylated intermediate of TC by the aid of microsomal metabolism is more important than the well known nitrosation mechanism under acidic condition such as in gastric juice in rats and in simulated gastric juice.

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The metabolism of trichloroethylene (TRI) and its metabolites, chloral hyrate (CH), trichloroethanol (free-TCE) and trichloroacetic acid (TCA), were examined in the isolated perfused rat liver, to clarify the role of the liver in the metabolism of TRI. TRI was rapidly converted to TCE and TCA by the perfused liver. TCA was produced from TRI about 2.5 times greater than was total-TCE. CH was metabolized to TCE and TCA immediately. TCA was also a dominant metabolite of CH over total-TCE. TCE(free type) was speedily conjugated by the liver. A portion of TCE was converted to TCA. Less than 10% of these metabolites produced by the liver were excreted into the bile. Most of them appeared in the perfusate.

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The inhibitory effects of 5-chloro-7-iodo-8-hydroxy-quinoline (clioquinol), methylmercuric chloride and 4-hydroxyaminoquinoline-N-okide(4-HAQO) on DNA, RNA and protein syntheses in the neonatal rat superior cervical ganglion (SCG) were studied in relation to the action of mouse 2.5S nerve growth fattor (NGF), using organ cultures. RNA and protein syntheses in SCG were stimulated approximately 3- and 2-fold, respectively, by NGF (1 μg/ml), but the DNA synthesis was only slightly or not at all stimulated. Methylmercuric chloride and 4-HAQO dose-dependently inhibited DNA, RNA and protein syntheses, either in the presence or in the absence of NGF. On the other hand, clioquinol (up to 100 μM) slightly or not at all inhibited RNA synthesis in the absence of NGF ; however, it did abolish the NGF-induced stimulation of RNA synthesis in the presence of NGF. The DNA and protein syntheses were dose-dependently inhibited by clioquinol, either in the presence or in the absence of NGF. We conclude from this study that the interaction between clioquinol and the functions of NGF raises the question of a possible toxicity of the drug on specifit neurons.

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The types and incidences of spontaneous tumors in F344/DuCrj rats were examined in 960 males and 959 females served as the control groups of separate twelve 2-year chronic and oncogenicity studies carried out during a 1978-1983 period. The major tumors occurred at more than 5% incidence were leukemia (mononuclear cell), testicular interstitial cell tumor, preputial gland adenoma, pituitary anterior adenoma, thyroid C-cell adenoma, adrenal pheochromocytoma and subcutis fibroma for males, and leukemia, uterine endometrial polyp, pituitary anterior adenoma, thyroid C-cell adenoma and mammary gland adenoma/fibroadenoma in females. Analyses on age-related occurrence of tumors revealed that the incidences of most of the major tumors in males attained already to the plateau between 85 and 97 weeks of age while those in females showed a steep rise during the last interval of observation, 98 to 110 weeks of age. An intralaboratory heterogeneity in incidence was observed in the thyroid C-cell adenoma and the adrenal pheochromocytoma for males, and the anterior pituitary adenoma for females.

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The effect of croton oil on intestinal carcinogenesis by methylazoxymethanol acetate (MAM) was examined in ACI/N rats. Twenty seven male and 28 female ACI/N rats were given a single intragastric intubation of MAM at a dose of 25 mg/kg body weight, followed by croton oil at 0.25 ml/kg body weight, 3 times a week, by gastric intubation until the termination of this experiment (365 days). The animals had diarrhea with administration of the croton oil, but the diarrhea had no effect on their gain in weight. Rats from all groups surviving more than 216 days were counted as effective animals. Seventeen out of 54 effective rats which were treated with MAM and croton oil developed intestinal tumors and the incidence of the intestinal tumors was significantly less than that of the group treated with MAM alone (30 out of 50 rats, P<0.01). The average number of tumors per rat in the experimental group which was treated with MAM and croton oil (0.6 ± 1.1) was also smaller than that in the group which was treated with MAM alone (1.0 ± 1.8), although the difference was not significant. These results suggest that croton oil may suppress some tumor growth at the proper dose in intestinal carcinogenesis which is initiated by MAM.

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We attempted to induce neurological disorders in mice by a single administration of various doses of ptaquiloside (PT) within 24 h after birth. Animals which survived for a long period after treatment showed a reduction in body weight, but did not develop any gait disturbance. On the other hand, in treated animals which died before beginning to walk, karyorrhexis in the external granular layer of the cerebellum and karyorrhexis and rosette formation in the neuroblastic layer of the retina were present. In addition, treated animals showed karyorrhexis and great reduction in the number of the cells in the thymus, suggesting cytotoxic and cytolytic effects of alkylating agents on lymphocytes in this organ.

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An acute administration of MCI-2016 at the doses of 30, 100 and 300 mg/kg (p.o.), and 10, 20 and 30 mg/kg (i.p.) produced a slight CNS depression in rats, such as, sedation, ptosis, decrease in motor activity and systemic muscle relaxation. In a direct physical dependence test, rats were fed the MCI-2016-admixed food together with drinking water ad libitum for 24 hours daily for 51-71 days (mean MCI-2016 intake 29.9-210.7 mg/kg/day), on the gradedly increased dosage schedule with a dosage level of 0.25 and 0.5 mg/g food to 4 mg/g food. In a natural withdrawal following administration of MCI-2016, no significant withdrawal sings were observed in any group. In a naloxone-precipitation test the rats that were treated with MCI-2016-admixed food did not show any withdrawal sings. In a substitution test in either morphine or barbital dependent rats, no suppression of withdrawal sings or maintenance of dependence were observed by cross-administration of MCI-2016. In conclusion, MCI-2016 was considered to have no physical dependence potential.

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A major challenge facing toxicologists is the development of improved human risk assessment methods based on understanding the mechanisms of chemical carcinogenesis in animal and human cells. Such methods will enable us to close the gap between experimental toxicity data and their relevance to human health. We have used 1, 3-butadiene (BD), a potent mouse carcinogen but weak oncogen in the rat, as a model compound to determine if genetic toxicity results from animal and human cells can aid in extrapolating animal toxicity data to man. Sister chromatid exchange and micronucleus induction data for BD parallel the chemical's carcinogenicity in the mouse and rat. Effort is underway to determine BD's genotoxic effects in human cells in vitro and to compare these effects in corresponding cultured rodent cells. This approach will help identify which species is a better predictor of the human response. If the BD research proves useful in assessing its hazard to man, similar methods can be extended to other major chemicals.

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Several thousands of new chemical entities are synthesised each year in the laboratories of the world. Currently there are estimated to be some 100, 000 substances used commercially of the 7 million chemicals recorded by chemical abstracts (Ca 1.5%). Public attention is mainly attracted to the potential life threatening and ill health effects of chemicals such as systemic poisoning, carcinogenicity, teratogenicity and mutagenicity, although there are relatively few proven human chemical carcinogens, teratogens or mutagens. Many substances have been examined in animal toxicity studies for their acute toxic effects, far fewer for chronic toxic effects. The public's perception is that chemicals are toxic. In Our laboratory, minimal to no lethal toxic effects were recorded for more than 60% of substances examined at doses below 2000mg/kg/bwt by either oral or dermal routes. A similar spectrum of chemicals did not elicit skin or ocular irritant or skin sensitisation response in 70-80% of studies. Perversley although toxicity studies reasonably predict the probable human response following exposure, they are a focus of a strong public lobby supported by many scientists to curtail studies in experimental animals. Consequently, much effort is devoted towards the development of "alternative" in vitro and ex-vivo procedures. Often these are empirically based without consideration of the underlying fundamental physiology, biochemistry or toxic mechanism of action. Consequently there can be an over-estimation or expectation of their ability to predict potential toxicity. Attention is seldom directed towards the design requirements of the validation studies needed to test, performance and reproducibility and the evaluation of the parameters of sensitivity and specificity. Additionally the influence of the prevalence of the chemicals having the toxic effects to be detected in the sample population is often overlooked. The prevalence of chemicals with positive effects expected in the sample population on the parameters of test sensitivity and specificity, establishes whether the level of test sensitivity and specificity will be sufficient to give an adequate confidence to the predictivity of the assay. These parameters have been examined with regard to the development of pre-evaluation procedures for the assessment of toxicity.

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