Time sequence of cancer occurrence. Implications in low level radiation risk assessment.

A total of 8,229 C57 Black mice of both sexes were randomly assigned to various groups. In some groups, mice aged 33 +/- 3 days were submitted to either sham, neutron or cobalt external radiation at 32, 45, 63, 88 and 123 mGy or at 18, 25, 36 and 51 cGy dose levels, respectively. In other groups, mice either at birth or weaning, were injected with tritiated thymidine or tritiated water, or were given tritiated water as drinking water for the entire lifespan. The main purpose of the experiment was to investigate the low dose-response relationship of cancer induction, especially leukemogenesis and to evaluate the excess risk, using actuarial age-specific rates. Following neutron or cobalt exposure, the phenotypic occurrence of lymphocytic lymphomas was earlier in appearance and higher in yield during the first decades of lifespan in irradiated groups versus matching controls, whereas such occurrence was markedly lower in yield at a later age. Under parallel experimental conditions, induction of reticulum cell lymphomas, however, was uniformly enhanced throughout the entire lifespan. Induction rates of all tumors (reticular and solid) pooled were significantly increased, and more so following cobalt than neutron irradiation. In mice injected with tritiated thymidine, the overall tumor incidence was increased monotonically throughout the lifespan. In mice exposed to tritiated water, the incidence of lymphocytic lymphomas was markedly increased throughout the lifespan, whereas no such effect was observed for reticulum cell tumors. In the light of tumor data analysis, it appears that selection of a particular type of tumor as a dependent variable for dose-response assessment cannot disregard the primary modulation of the whole tumor spectrum, In C57 Black murine leukemogenesis, the shape and structure of the dose-response regression curve over the entire lifespan dose not fit the linear-quadratic model. It is, however, theorized that our data are consistent with the two-mutation clonal expansion model, assuming creation of initiated cells which are added to the pool of spontaneously occurring initiated cells and implying that the excess risk is initially high at early age and then decreases with increasing age following exposure. It is concluded that murine radiocarcinogenesis investigation may contribute to improving the assessment as well as understanding the underlying mechanisms of low level radiation hazards.

Six month oral toxicity study of trinitrotoluene in beagle dogs.

This study was conducted to evaluate the toxicity of the munitions compound 2,4,6-trinitrotoluene (TNT; CAS Reg. No. 118-96-7) in beagle dogs when administered daily for 26 weeks by capsule. Groups of six dogs per sex received TNT at doses of 0 (vehicle controls), 0.5, 2, 8, or 32 mg/kg/day. Toxicologic endpoints included clinical signs, body weights, food consumption, clinical biochemistry, hematology, urinalyses, organ weights, and gross and tissue morphology. The major toxic effects following the oral administration of TNT to dogs included hemolytic anemia, methemoglobinemia, liver injury, splenomegaly with accompanying histologic lesions, and death. Only the highest dose given proved to be lethal. Hepatocytic cloudy swelling and hepatocytomegaly were apparent at all doses tested. Thus, a no observable effect level was not established in this investigation.

[Comparative incidence of reticuloendothelial tumors in C57BL mice after exposure to tritiated water]. / Incidence comparative des tumeurs réticulo-endothéliales chez les souris C57BL après exposition à l'eau tritiée.

A total of 2,377 C 57 Bl/6M mice were assigned to control groups and experimental groups exposed to tritiated water administered as a pulse injection or in drinking water, at a dose of 1.0 microCi per injection or per ml of drinking water. Weanlings were observed for the duration of life span. Data analysis was based on two coefficient estimates (1) individual carcinogenic induction coefficient and (2) specific tumorigenic induction coefficient. The carcinogenic potency of tritium was found to be dual in nature in enhancing the absolute induction of lymphocytic lymphomas in both sexes as well as their relative induction in competition with reticulo-endothelial tumors of other types.

The pathologic response of the liver and thyroid of the rat to potassium prorenoate (SC-23992).

A 3-month dose range finding study in preparation for a 2-yr carcinogenicity study of potassium prorenoate (SC-23992), a steroid with an antihypertensive profile, is reported. The drug was administered by gavage once daily at doses of 10, 30, and 100 mg/kg/day to Charles River CD rats. Treatment was terminated at 13 weeks and 10 randomly selected animals from each treatment group were killed and necropsied. The remaining 10 animals in each dose group, including controls, were maintained for an additional 4 weeks, in order to investigate reversibility of changes, and then were killed and necropsied. Dose-related increases in thyroid-stimulating hormone (TSH) levels were observed in treated animals of both sexes during the dosing period and the changes were statistically significant and correlated with an increased thyroid weight in females at 13 weeks. Dose-related morphologic changes in the thyroid, observed by light and electron microscopy, were compatible with the effects of TSH stimulation. Liver weights, which increased, were dose-related. In females the increase was statistically significant at the high dose at 2, 4, and 13 weeks. In males it was significant at the high dose at 13 weeks. Microsomal enzyme levels were increased in a time- and dose-related manner with higher values in females than in males. The pattern of enzyme induction was of the type exemplified by pregnenolone- 16-alpha-carbonitrile. Morphologic changes in the liver showed centrilobular hepatocyte enlargement with smooth endoplasmic reticulum membrane proliferation confirmed by electron microscopy. All positive findings returned to normal after the 4-week treatment-free period. The relationship between the thyroid stimulation to liver enzyme induction is of interest. Evidence is presented here that in the presence of SC-23992, TSH stimulation and liver enzyme induction occurred. The possibility that the liver metabolism stimulates the thyroid T3, T4 elimination with secondary TSH activity is a possible explanation, but on the basis of existing information, direct action by SC-23992 on the thyroid cannot be excluded.

Oesophagostomiasis in feral monkeys (Macaca mulatta).

For periods of 3, 6, and 12 months, 104 feral rhesus monkeys (Macaca mulatta) were on test. At the time of necropsy, 26 had caseous granulomatous lesions in the submucosa of the colon consistent with oesophagostomiasis. Five also had histologically identified granulomatous lesions without caseation of various colonic and more distant arterioles. The lesions were seen in the submucosa and subserosa of the colon, the kidney, the adventitial tissue of the prostate, the pancreas, and the heart. Presumptive evidence of the migration of the parasite was found in the adventitial tissue of the esophagus. Fragments of the larvae in arterioles and the caseous submucosa of the colon were consistent morphologically with the species Oesophagostomum. Acellular masses of what was interpreted as cuticle of a molting parasite were found in the lung. A mature female nematode was found encysted in the lung. The identity of that parasite and the cuticle has not been established.

[Hereditary intestinal tumor observed after irradiation of multiple generations of a male germinal line of C57BL/6 mice]. / Tumeur intestinale héréditaire observée après irradiation de générations multiples d'une lignée germinale mâle de la souris C57BL/6.

An heritable multiple intestinal adenocarcinoma was observed in the offspring of an outcross between a male (or female) parent originating from our C57 Black/6M strain and his female (or male) mating counterpart originating from an experimental subline of the same strain, propagated following multigeneration exposure of the male parent to low level tritium, as drinking water (10 microCi/ml) for 35 days prior to mating.

Chronic effects of dietary exposure to amosite and chrysotile asbestos in Syrian golden hamsters.

Bioassays of amosite, short-range (SR), intermediate-range (IR) or intermediate-range chrysotile asbestos in combination with the intestinal carcinogen 1,2-dimethylhydrazine dihydrochloride (DMH) were conducted with male and female Syrian golden hamsters. Amosite and both forms of chrysotile asbestos were administered at a concentration of 1% in pelleted diet for the entire lifetime of the hamsters starting with mothers of the test animals. Group sizes varied from 125-254. There was no adverse effect on body weight gain or survival by either type of asbestos or by IR chrysotile asbestos in combination with DMH. A significant increase (p less than 0.05) in adrenal cortical tumors was observed in male hamsters exposed to SR and IR chrysotile asbestos and in females treated with IR chrysotile asbestos when compared to the pooled control groups. However, statistical significance (p less than 0.05) was lost when these dosed groups were compared with temporal control groups. Neither of the male or female amosite asbestos groups showed increased neoplasia in any tissue or organ compared to the control groups. The cocarcinogen studies using IR chrysotile asbestos and 1,2-dimethylhydrazine dihydrochloride were considered inadequate because there was no increase in intestinal neoplasia in the DMH group.

Animal models for human diseases.

PIP: The use of animal models for the study of human disease is, for the most part, a recent development. This discussion of the use of animal models for human diseases directs attention to the sterile period, early advances, some personal experiences, the human as the model, biological oddities among common laboratory animals, malignancies in laboratory animals, problems created by federal regulations, cancer tests with animals, and what the future holds in terms of the use of animal models as an aid to understanding human disease. In terms of early use of animal models, there was a school of rabbis, some of whom were also physicians, in Babylon who studied and wrote extensively on ritual slaughter and the suitability of birds and beasts for food. Considerable detailed information on animal pathology, physiology, anatomy, and medicine in general can be found in the Soncino Babylonian Talmudic Translations. The 1906 edition of the "Jewish Encyclopedia," has been a rich resource. Although it has not been possible to establish what diseases of animals were studied and their relationship to the diseases of humans, there are fascinating clues to pursue, despite the fact that these were sterile years for research in medicine. The quotation from the Talmud is of interest: "The medical knowledge of the Talmudist was based upon tradition, the dissection of human bodies, observation of disease and experiments upon animals." A bright light in the lackluster years of medical research was provided by Galen, considered the originator of research in physiology and anatomy. His dissection of animals and work on apes and other lower animals were models for human anatomy and physiology and the bases for many treatises. Yet, Galen never seemed to suggest that animals could serve as models for human diseases. Most early physicians who can be considered to have been students of disease developed their medical knowledge by observing the sick under their care. 1 early medical investigator proposed that an aggressive invasive cancer of the dog that he had observed be used to study cancer in a generic sense. Other researchers who recognized the value of animals in medical research were Jenner, Claude Bernard, and Pasteur. The human can also serve as an animal model. Some of those situations are presented, and in all a common theme exists. There was no known animal model that could be used, and in some cases the situation has not changed today. In all cases the discoveries must be regarded as serendipitous. The state of the art of the pathology of laboratory animal diseases and neoplasia is unsatisfactory. There is much empirical speculation and little substance. Cancer studies with mice and rats as now conducted are of minimal value. Although a tradition of excellence in the use of animal models to help understand human disease has been established, much remains to be learned.^ieng

Effects in animals of chronic administration of spironolactone--a review.

Spironolactone, an aldosterone antagonist, has been found effective in the treatment of certain forms of hypertension, ascites, and edematous conditions. Since patients may receive daily doses of spironolactone for many years, it is important to determine the chronic effects on tissues. This study reviews the tissue changes in rats, dogs, and monkeys receiving spironolactone daily for up to two years. Dose levels were frequently in excess of 100 times the recommended human dose. The pituitary, adrenals, and kidneys of all animals showed no significant changes. Histologic changes were noted in rat livers, thyroid, and male internal genitalia. There were alterations in monkey testes and male mammary glands. This study found no evidence to suggest that spironolactone is tumorigenic or carcinogenic. Species differences in metabolism may account for the diversity of tissue observations.

Comparative incorporation of tritium from tritiated water versus tritiated thymidine, uridine or leucine.

Whereas the radiotoxicity of tritium has been extensively studied, comparatively little information exists on its long-term effects as a potential environmental pollutant, particularly at small dosage. This investigation was primarily aimed at assessing comparatively a possible carcinogenic potency of tritiated water versus radioactive precursors of DNA, RNA and proteins, namely tritiated thymidine, uridine and leucine in C57 Black mice. Tritium is largely released in the environment in the form of tritiated water. There are many uncertainties, however, as to how tritium is incorporated from tritiated water into cell constituents quantitively and qualitatively. In 1965, we reported on the carcinogenic effect of tritium in the form of tritiated thymidine on newborn C57 BL mice in the dose range of 0.3--1.5 muCi/g [Mewissen. 1965]. Hence the selection of tritiated water, and of tritiated precursors, in an attempt to evaluate their respective role in the tritium transfer process and to correlate their possible late effects with their specific patterns or sites of incorporation. This study deals with tritium incorporation from tritiated water and various precursors at the 1 or 10 muCi level. RSA values, i.e., the ratio of organically bound tritium per hydrogen content of dry tissue over aqueous tritium per hydrogen content of water, were estimated for newborn, juvenile and adult mice, at various time intervals (1, 8, 15, 22 and 29 days) following single administration of tritiated water, tritiated thymidine, uridine or leucine. The data available at this time show that administration of tritiated water (or precursors) result in a complex time dependent and age dependent residual activity dynamics both in the organic component and in the aqueous fraction of tissue. A few preliminary conclusions can be made. Following a single acute or brief exposure to tritiated water, values of activity become exceedingly small after a relatively short time period. In a steady state equilibrium, resulting from chronic exposure to tritiated drinking water, RSA values tend to stabilize. However, wide variations between various organs are to be expected, as suggested by their respective RSA values following a single exposure. In view of these observations, it would seem that a realistic estimate of the internal dose to the radiosensitive nucleus must take into consideration the age dependent incorporation of tritium from tritiated water, as well as the variation between organs. The carcinogenic risk has often been estimated from a uniform dose dependency model. The influence of time and space microdistribution of dose within tissues and more particularly at specific sites (such as DNA, RNA or protein) has received, as yet, little attention, as well as the relative contributions of the time sequence of dose absorption during the usually long latency period. Such factors, among others, may be critical in carcinogenesis from internal irradiation...

[Epidemiology of C57 black/6M mouse strain: statistical findings in a control population]. / Epidémiologie de la souris C 57 black/6 M: données actuarielles d'une population témoin.

Non-linearity in age specific gompertzian rates regression versus age was observed in actuarial analysis of all causes of death, tumor incidence and tumor/tumor-host index in 503 male and 497 female control C57 Black/6M mice. The overall tumor incidence averaged 66.7% in males and 84.4% in females during a maximum lifespan of 1,300 days. In males as well as in females, time related incidence peaks were identified for lymphocytic lympho-sarcomas, reticulum cell sarcomas, histiocytic type and reticulum cell sarcomas of reticular type.

Stable reagent for the detection of antibody to the specific fraction I antigen of Yersinia pestis.

A stable hemagglutinating antigen for detection of fraction I (FR-I) antibody of Yersinia pestis (Pasteurella pestis) is described. The antigen was prepared by sensitizing tanned, pyruvaldehyde-treated sheep erythrocytes (PAT SRBC) with FR-I antigen. Preliminary standardization by titration of each lot of FR-I was required to minimize the effect of molecular heterogeneity of specific FR-I antigen and to eliminate nonspecific reactions caused by the presence of a minor antigenic contaminant. In tests with sera from rabbits, dogs, and humans, FR-I PAT SRBC were as reactive as the previously employed standard antigen, FR-I-sensitized tanned erythrocytes. Fluid suspensions of FR-I PAT SRBC stored at 4 C for 3 months, or lyophilized preparations stored at ambient temperature for 6 months, showed no loss in antigenic activity.