Multiple organ carcinogenicity of 1,3-butadiene in B6C3F1 mice after 60 weeks of inhalation exposure.

Groups of 50 male and 50 female B6C3F1 mice were exposed 6 hours per day, 5 days per week, for 60 to 61 weeks to air containing 0, 625, or 1250 parts per million 1,3-butadiene. These concentrations are somewhat below and slightly above the Occupational Safety and Health Administration standard of 1000 parts per million for butadiene. The study was designed for 104-week exposures but had to be ended early due to cancer-related mortality in both sexes at both exposure concentrations. There were early induction and significantly increased incidences of hemangiosarcomas of the heart, malignant lymphomas, alveolar-bronchiolar neoplasms, squamous cell neoplasms of the forestomach in males and females and acinar cell carcinomas of the mammary gland, granulosa cell neoplasms of the ovary, and hepatocellular neoplasms in females. Current workplace standards for exposure to butadiene should be reexamined in view of these findings.

Natural history of body weight gain, survival, and neoplasia in the F344 rat.

This study involved the fact that knowledge of the natural incidence of neoplastic lesions is essential for interpretation of experiments designed to reveal the effects of potential carcinogens. Although the F344 rat is widely used in chronic (2-yr) testing programs, the natural history of neoplasia after 24 months is not known; thus this study, with 529 male and 529 female inbred F344 rats, was designed to deal with this aspect. This report also included information on growth and longevity. In addition, the tumor rates found in this study were compared with 2-year historic control tumor rates; results revealed the following. 1) Maximum mean body weights were 468 and 330 g for males and females, respectively. Peak weight in males was reached at 77 weeks of age and in females, at 107 weeks of age. 2) There was no clear sex difference in longevity; a median life-span (50% survival age) or 28 months was recorded in both sexes. 3) Variety of neoplastic lesions in animals that were allowed to live out their life-span was not greater than that in animals that were killed between 110 and 116 weeks of age; thus older age was not characterized by unique neoplasms. 4) The incidence of certain neoplasms increased markedly after 110-116 weeks. The data indicated that life-span studies in F344 rats had no advantages over 2-year studies. However, availability of life-span data is essential for interpretation of the 2-year studies.

Guidelines for combining neoplasms for evaluation of rodent carcinogenesis studies.

In a continuing review of long-term toxicology and carcinogenesis studies in rats and mice, the National Toxicology Program (NTP) is confronted with many problems concerning the interpretation of tumor data. A frequently raised question is: "Should certain neoplasms be combined for overall assessment of rodent carcinogenesis data?" NTP policy is that certain neoplasms may be combined for statistical assessment of tumor data and that hyperplastic responses may be used as supportive evidence. The primary reason for combining neoplastic lesions is to gain more insight into the evidence of the carcinogenicity of a given chemical in that species of animal. This report gives the rationale, criteria, and guidelines used by the NTP for combining neoplasms for the evaluation of long-term rodent toxicology and carcinogenesis studies. The guidelines are based mainly on lesions occurring in the F344/N inbred rat and (C57BL/6 X C3H)F1 mouse and may or may not be appropriate for other strains or species. The concepts of combining neoplasms and sites should be viewed in terms of the study as a whole, since tumor formation is only one of many responses caused by chemicals in mammals. The resulting information becomes part of the "weight of the evidence" for estimating the potential hazard of a given chemical.

Biological and clinical consequences of longitudinal studies in rodents: their possibilities and limitations. An overview.

Rats and mice are used in gerontological research primarily because of their relatively short life spans, ease of handling, and the relatively low costs of production and maintenance under controlled environmental conditions of large number of rodents as compared to larger laboratory animal species. They are being used as models for studying intrinsic aging processes, processes that give rise to diseases associated with aging, and the influence of environmental factors on these processes. Contrary to the situation in man, longitudinal studies in rodents can be conducted under well controlled environmental conditions. It has been shown that multiple pathology, the hallmark of aging in man, also occurs in inbred strains of rodents. Some of these lesions are genetically determined and some of them are randomly distributed amongst members of the same inbred strain. Serial killing experiments are necessary to obtain information on the time of development of these lesions in order to interpret properly the outcome of investigations. Furthermore, it has been shown that a considerable variation can exist in the observed maximum ages of the longest-lived animals in cohorts of rats kept under well controlled conditions. For this reason, caution should be exercised in interpreting data from studies which claim maximum lifespan prolongation.

Vasopressin and the pathogenesis of chronic renal failure.

1. Partial (5/6) renal ablation was performed in Long Evans rats treated with vehicle or a vasopressin V1-receptor antagonist, in control Long Evans rats, and in homozygous Brattleboro rats which lack endogenous vasopressin. 2. In control and vasopressin-blocked Long Evans rats, 3 weeks following partial renal ablation, systolic blood pressure was 215 +/- 5 and 199 +/- 9 mmHg and, urinary protein excretion was 54 +/- 4 and 50 +/- 3 mg day-1, respectively. 3. The pressor response to exogenous vasopressin was significantly (P less than 0.05) reduced in rats treated with the V1-receptor antagonist (ED50 mmHg 5.0 +/- 1.6 vs. 0.09 +/- 0.01 micrograms kg-1). 4. In control Long Evans and in Brattleboro rats, 3 weeks following renal ablation, systolic blood pressure was 204 +/- 10 and 191 +/- 7 mmHg, and urinary protein excretion was 97 +/- 27 and 71 +/- 5 mg day-1, respectively. 5. Histological examination of the remaining kidney tissue demonstrated significant glomerular hyalinization following renal ablation but no differences between any of the groups. 6. The data indicate that neither vasopressin nor the urinary concentrating mechanism is likely to be involved in the hypertension and proteinuria associated with partial renal ablation.

Actuarial analysis of the hazard for mammary carcinogenesis in different rat strains after X- and neutron irradiation.

Mammary carcinogenesis in three different rat strains has been studied after single and fractionated irradiations with X-rays and monoenergetic neutrons of three energies. The aims of the programme are the investigation of the nature of the dose-effect relationships, and the determination of the relative biological effectiveness (RBE) of neutrons. Histopathological examinations of tumours has been completed and dose-effect relations are reported separately for the induction of benign and malignant lesions. Appropriate corrections have been made for competing risks in the tumour rate analysis. The probability curves for survival without evidence of tumours have been described by Weibull distributions. This continuous parametric failure-time model is used to derive the relative excess hazard for exposure to X-rays and neutrons. The different rat strains show considerable differences in susceptibility for the induction of cancer by radiation. In general linear dose-response curves have been observed for mammary tumourigenesis in the three rat strains for both X-rays and fast neutrons. Within the statistical precision of the data a dependence of the RBE on neutron dose cannot be recognised. The highest RBE values, varying between 7 and 15 for different types of tumours in the three rat strains have been observed for 0.5 MeV neutrons. These RBE values are lower in general than those observed by other groups for beams of comparable energy.

Effects of X-irradiation, ovariohysterectomy and estradiol-17 beta on incidence, benign/malignant ratio and multiplicity of rat mammary neoplasms--a preliminary report.

An overview is given of the effects of X-irradiation, ovariohysterectomy and estradiol-17 beta administration on mammary tumorigenesis in females of 3 rat strains, viz. the WAG/Rij, BN/BiRij and SD. The 3 rat strains differed significantly in their spontaneous mammary tumor incidence. Female SD rats had the highest incidence (47%) and female BN/BiRij rats the lowest (17%). Female WAG/Rij rats had an intermediate incidence of 29%. The benign/malignant ratio in female WAG/Rij, BN/BiRij and SD rats was 1.0, 2.0 and 7.3, respectively. The average number of mammary gland neoplasms per untreated tumor-bearing female was 1.2 in the WAG/Rij, 1.0 in the BN/BiRij and 1.6 in the SD, whereas the respective maximum numbers were 2, 1 and 5. Ovariohysterectomy almost entirely prevented mammary tumor formation in all 3 rat strains, whereas estrogen treatment enhanced it. In addition, estrogen treatment resulted in an increased number of mammary tumors per tumor-bearing female and changed the benign/malignant ratio into the direction of malignant. X-irradiation increased the mammary tumor incidence in all 3 rat strains, especially of the benign tumors. Estrogen potentiated the effect of irradiation. An effect of irradiation on mammary tumorigenesis was not observed in ovariohysterectomized females of all 3 rat strains.

The gene transfer-misrepair hypothesis of radiation carcinogenesis tested for induction of mammary tumours in rats.

Mammary tumour induction was studied in female WAG/Rij rats following exposure with single doses of 0.3 and 1.2 Gy gamma radiation and with the same total doses delivered in fractions of 2.5 and 10 mGy respectively at intervals of 12 h. All rats were implanted with pellets containing 2 mg of estradiol-17 beta prior to the irradiation. The occurrence of mammary carcinomas and of fibroadenomas was recorded. The relative excess hazard for tumour induction was lower for the fractionated regimens than for the single dose exposures. The results are compatible with the predictions of the gene transfer-misrepair hypothesis for radiation carcinogenesis.

Dimethyl methyl phosphonate induction of dominant lethal mutations in male mice.

The reproductive toxicity of dimethyl methyl phosphonate (DMMP) was studied in the male B6C3F1 mouse. Male mice were treated with 0, 250, 500, 1000, and 2000 mg/kg DMMP by gavage 5 days per week for 13 weeks. After 4, 8 and 12 weeks of treatment the male mice were mated to untreated CD-1 female mice. At the two highest doses (1000 and 2000 mg/kg) the chemical caused a dominant lethal effect (early resorptions). Groups of male mice (at 1000 and 2000 mg/kg), mated after a 15-week recovery period without chemical dosing, had a resorption rate comparable to the control group. After 13 weeks of dosing, the male mice showed no histopathologic changes of the reproductive organs, no abnormalities in sperm concentration or sperm morphology, no evidence for hormone imbalance, no signs of general toxicity, and no effects on the fertilization rate. The male B6C3F1 mouse was less responsive than the male Fischer 344/N rat to the reproductive toxic effects of DMMP.

Animals in aging research: requirements, pitfalls and a challenge for the laboratory animal specialist.

The prime goal of aging research is to gain some insight into the basic mechanisms underlying the aging process. The long lifespan and frequent mobility of humans as well as the legal and ethical constraints on human experimentation make man unsuitable for studying the aging process. Therefore animals, particularly rodents, are used in aging research. In studying the aging process in animals, one hopes to find means for the prevention or amelioration of at least some of the disabilities of old age in man. Many intrinsic and extrinsic factors can influence the outcome of animal experiments; hence an extensive monitoring program is a prerequisite in aging research. An important role in controlling the quality of the animals is reserved for the laboratory animal specialist. Since he is faced with all aspects of laboratory animal science, aging research is a challenging area for such a specialist.

[Nalidixic acid intoxication in two pregnant bitches (author's transl)]. / Nalidixinezuur intoxicatie bij twee drachtige teven.

To ensure prolonged survival, dogs with cyclic neutropenia should be protected against bacterial infection of exogenous or endogenous origin, particularly during the neutropenic episodes. One of the methods available to minimize the risk of infection in these dogs, is selective decontamination of the gastrointestinal tract by using antibiotics and/or chemotherapeutic agents, in conjunction with housing in a laminar-flow cabinet. Two pregnant bitches, some of the offspring of which were expected to be homozygous for the cyclic neutropenia allele, were decontaminated with nalidixic acid. Fourteen days after initiation of the antibacterial treatment, the two dogs died. Jaundice and seizures had been apparent in both animals prior to death. Histopathological examination revealed changes primarily in the liver, which were consistent with toxic hepatic necrosis and were characterized by severe centrilobular haemorrhage and disappearance of hepatocytes. Multiple haemorrhages were observed in other organs. Further clinical investigation in two other dogs strongly suggested that nalidixic acid was the cause of death in the two pregnant bitches.

Types and quality of animals in cancer research.

In addition to studies in man, animal models may serve as important tools in the detection of the etiology, biology and treatment of certain types of human cancers. Various models have become available by performing life span studies on 2 rat strains, viz WAG/Rij, BN/Bi and (WAG x BN) F1 hybrid and on Praomys natalensis. Several of these models are described. A basic prerequisite for these types of studies is the availability of animals of good quality. After a general description of the quality of laboratory animals the desirable health status of animals in cancer research is discussed.

Absence of anti-acetylcholine receptor antibodies in Praomys (Mastomys) natalensis.

It has been suggested in the past that Praomys (Mastomys) natalensis might be an animal model for human myasthenia gravis. This suggestion was based on the occurrence of thymomas and autoantibody to striated muscle in this animal species. Myasthenia gravis in man is associated with anti-striated muscle antibody and thymoma as well as antiacetylcholine receptor antibody. This prompted us to search for such autoantibodies in Mastomys. There was no evidence of anti-acetylcholine receptor antibody in any of the serum samples tested. The titres found in Mastomys correspond to those observed in human control sera. No difference was found in the number of alpha-bungarotoxin-binding sites at the motor endplate and in muscle extracts between animals with and without thymoma and with and without anti-striated muscle antibody. These findings lead to the conclusion that it is very unlikely that myasthenia gravis occurs with any frequency in Praomys (Mastomys) natalensis.

The value and significance of life span and scheduled termination data in long-term toxicity and carcinogenesis studies.

Consideration is given to the age association of lesions, the duration of long-term toxicity and carcinogenesis studies, and to the value and significance of including scheduled termination in such long-term studies. There is now enough evidence that age and cancer are associated. It is argued that the increase in incidence of lesions with age has such disadvantages that extension of the duration of the long-term toxicity and carcinogenicity study beyond 2 years is not warranted in most cases. Incorporation of scheduled termination in long-term studies gives more insight into the biologic behavior of toxic lesions and cancer and may enable one to make a distinction between "incidental" and "fatal" lesions. This distinction may be important for the statistical evaluation of data from chemical carcinogenesis studies.

Spontaneous renal lesions in five rat strains.

A survey of non-neoplastic and neoplastic renal lesions found in 5 rat strains, namely, ACI (August X Copenhagen Irish), A22807 (August), F344 (Fischer), M520 (Marshall), and OM (Osborne-Mendel) is given. The results from this survey indicate that the OM, M520, and ACI rat strains have major disadvantages for their use in long-term toxicology and carcinogenesis studies. Male OM rats had a high incidence of renovascular lesions which consisted of necrotizing arteritis or arteriolitis and intimal thickening of small arteries, and resembled renal lesions described in hypertensive rats and human patients. Predominant renal lesions in the M520 and ACI rat strains included extensive calculus formation at the pyramido-pelvic junction, which was often associated with proliferative pelvic transitional cell lesions and hydronephrosis. The ACI rat strain also had unilateral congenital renal agenesis in about 12% of the animals of either sex. Based on the spectrum of renal lesions observed in the 2 remaining rat strains, namely A28807 and F344, it is difficult to determine which one of the two should be preferred for long-term studies. The A28807 rat strain had less severe chronic renal disease than the F344 but had a higher incidence of pelvic transitional cell hyperplasia. The ultimate choice should be based on the spectrum, incidence, and severity of extra-renal lesions.

Membranous dysmenorrhea in the chimpanzee (Pan troglodytes). A report of four cases.

A macroscopic and histologic description of membranous dysmenorrhea in chimpanzees is given. The similarity of these cases to those in women make the chimpanzee an interesting model for studies on the presently unknown etiology of membranous dysmenorrhea.

Primary cardiac hemangiosarcomas induced by 1,3-butadiene in B6C3F1 hybrid mice.

Proliferative vascular lesions of the heart were found in mice exposed chronically to 1,3-butadiene by inhalation with an overall incidence of 30% in males and 43% in females. Based on histological criteria, the lesions were subclassified as endothelial hyperplasia with an incidence of 7% in males and 13% in females and hemangiosarcoma with an incidence of 23% and 30%, respectively. A dose-relationship for both lesions was observed in females, but not in males. The absence of a dose response in males was most likely due to the lower survival rate for high-dose animals (14%) when compared to the lower-dose animals (22%). Endothelial hyperplasia was characterized by widened vascular spaces lined by a single layer of plump endothelial cells. When cellular pleomorphism and piling up of endothelial nuclei were observed, the lesion was diagnosed as hemangiosarcoma. Ultrastructural examination of hemangiosarcomas revealed lumen formation, intercellular junctions and cytoplasmic filaments. Pinocytotic vesicles which are 1 of the characteristics of endothelial cells could not be identified with certainty. Weibel-Palade bodies were not detected in the neoplastic endothelium. Metastatic lesions were observed in liver, lung and kidney. To date, 1,3-butadiene is the only carcinogen reported that induces proliferative vascular lesions in the heart of mice.

A histopathological survey of aged Praomys (mastomys) natalensis.

This histopathological study shows that Mastomys develops a wide variety of neoplastic and nonneoplastic lesions with age. In comparing neoplastic lesions of Mastomys with those generally found in mice and rats, Mastomys is more or less unique with respect to the development of lymphoepithelial thymomas (40%), parathyroid adenomas (11%), prostatic adenocarcinomas (5%), and gastric carcinoids (4%) and the absence of brain, lung, and mammary tumors. Of the nonneoplastic lesions, prostatic (38%), thymic (12%) and parathyroid (11%) hyperplasia, and moderate to severe generalized degenerative joint disease (96%) occur rarely in mice and rats. Within the limits of this study, in which the age of the animals ranged from 18 to 39 months, a clear-cut age-related pattern was seldom found for most of the lesions occurring in Mastomys.

Clinicopathologic study of six cases of meningitis and meningoencephalitis in chimpanzees (Pan troglodytes).

Three fatal cases of purulent meningitis and one fatal case of thromboembolic necrotizing meningoencephalitis occurred in chimpanzees from the Primate Center TNO, The Netherlands. In addition, two apes had clinical signs of meningitis and were successfully treated. The severity of the residual hemiparesis and dysphagia in one of these two apes was such that it was killed for humane reasons. The histopathological diagnosis was chronic active meningoencephalitis. Streptococcus pneumoniae was isolated from five apes and Klebsiella pneumoniae from one. In the majority of cases, the primary site of infection was the upper respiratory tract. After reducing the population density, initiating a vaccination program using a commercially available human polyvalent pneumococcal vaccine, and changing the cleaning procedure of the animal facilities, no other cases of meningitis or meningoencephalitis have occurred in the chimpanzee colony in the ensuing 3.5 years.

Effects of sensitization to dinitrochlorobenzene (DNCB) on clinical pathology parameters and mitogen-mediated blastogenesis in cynomolgus monkeys (Macaca fascicularis).

Immunotoxicologic testing of drug candidates and environmental contaminants is of growing importance. Cutaneous delayed type hypersensitivity (DTH) is a convenient way of testing immune function in vivo. However, DTH testing must not interfere with interpretation of other relevant parameters. We have evaluated the effects of sensitization and challenge with dinitrochlorobenzene (DNCB) on clinical parameters routinely evaluated in toxicity testing and on lectin-mediated blastogenesis. Female cynomolgus monkeys were sensitized to DNCB with 4 daily applications of DNCB in acetone to the skin of the axilla. Fifteen days later, the monkeys were challenged for DTH by applying DNCB to the antecubital skin. Skin fold thickness was measured and the macroscopic appearance of the challenge site was scored 24 and 48 hr after challenge. All 5 monkeys were successfully sensitized to DNCB. There was a significant increase in the mean skin fold thickness (compared to pre-challenge thickness) of 2 mm at 24 hr and 1 mm at 48 hr (p less than 0.001). The clinical score of the challenge site was also increased. Histologic examination of the sensitization and challenge sites from a second group of monkeys exposed to DNCB in an identical manner showed the perivascular inflammatory cell infiltrate typical of DTH. Evaluation of hematologic parameters at days 7, 14, and 21 revealed no change in the erythron at any interval and a mild decrease in total WBC, neutrophil and lymphocyte counts on day 7 in 4/5 monkeys. The WBC parameters remained within the normal range and returned to pre-sensitization values at the later intervals.(ABSTRACT TRUNCATED AT 250 WORDS)