Morphology of experimentally induced tumors of the sympathetic nervous system in rats.

Seventeen tumors of the sympathetic nervous system were discovered in offspring of rats exposed in utero at a single dose of 80mg/kg of N-nitrosoethylurea at the day 16-19 of pregnancy, and then to constant light regimen. These tumors were classified as follows: benign--ganglioneuroma (six cases) and malignant--ganglioneuroblastoma (four cases) and neuroblastoma (seven cases). The most frequent location was in the sympathetic trunk in the mediastinum and in the retroperitoneal space. Morphological features of these induced tumors represent a model for similar neoplasms in humans in childrens' age.

Effect of light/dark regimen on N-nitrosoethylurea-induced transplacental carcinogenesis in rats.

Pregnant females were randomly subdivided into three groups (24 rats per group) and kept at the 12:12 h light/dark regimen (group 1), at the constant light illumination (24 h a day, group 2) or at the continuous darkness (group 3). N-nitrosoethylurea (NEU) has been injected into the tail vein of all rats (80 mg/kg) on the 18-19th day of the pregnancy. After the delivery the lacting dams and their progeny during the lactation period (1 month after delivery) were kept also at the three different light/dark regimens. Then all offspring from each group was kept at the 12:12 h light/dark regimen, males and females separately, and were observed until natural death. The exposure to constant light significantly promoted the transplacental carcinogenesis whereas the exposure to constant darkness inhibited it. The incidence of total tumors, tumors of both a peripheral nervous system and kidney was 2.6; 2.5 and 8.5 times higher, and survival significantly shorter, correspondingly, in rats from the group 2 exposed to the constant light regimen as compared to the group 1 (12:12 h light/dark regimen) (P<0.05). On the other hand, the exposure to the continuous darkness during the pregnancy and the lactation period significantly inhibited the transplacental carcinogenesis in the offspring of rats treated with NEU. The incidence of total tumors, tumors of a peripheral nervous system was by 2.4 and 2.7 times less, and survival longer, respectively, in exposed to the darkness rats from the group 3 as compared to the group 1 (12:12 h light/dark regimen) (P<0.05). Thus, our data firstly have shown the modifying effect of light-dark regimen on the realization of the transplacental carcinogenesis induced by NEU in rats.

[Modifying effect of light and electromagnetic field on development of mammary tumors induced by N-nitrosomethyl urea in female rats]. / Modifitsiruiushchee vliianie rezhima osveshcheniia i élektromagnitnykh polei na razvitie opukholei molochnoi zhelezi indutsiruemykh n-nitrozometilmochevinoi u samok krys.

Female rats aged I month and older were kept indoors in darkness, under lighting for 24 hours or exposed to ordinary lighting (light--12 hrs; darkness--12 hrs). Three weeks after the beginning of the experiment, they received N-nitrosomethyl urea (NMU) treatment in the dose of 50 mg/kg, intravenously, at weekly intervals, and were exposed to alternating 50 Hz (AMF) or static 0.2 oersted, (DMF) electromagnetic field radiation for 3 hrs, daily. Under usual lighting conditions, NMU treatment was followed by the development of mammary gland adenocarcinoma (MGA) in 31% of the animals. However, AMF or DMF treatment was followed by a shorter period of latency, without affecting MGA frequency. Constant lighting was found to stimulate a sharp increase in carcinogenesis: MGA frequency in groups receiving NMU, NMU+AMF or NMU+DMF was 57, 81 and 61%, respectively; latency period dropped by half as compared with usual lighting conditions. Conversely, the rats constantly kept in darkness revealed significant inhibition of mammary gland carcinogenesis, MGA frequency in NMU, NMU+AMF or NMU+DMF groups being 3, 4 and 2%, respectively. A blood serum--hormone assay showed constant lighting to decrease melatonin level and to increase prolactin concentration for all the modalities of carcinogenic treatment used. The results point to a significant promoting effect of constant lighting on mammary gland carcinogenesis by NMU in rats. This effect is potentiated by additional AMF or DMF treatment. Conversely, constant darkness inhibits mammary gland carcinogenesis and mitigates the pernicious effect of low-frequency electro-magnetic radiation.

Tumor induction in monkeys after administration of dimethylhydrazine.

1,2-Dimethylhydrazine (DMH) was administered subcutaneously to nine Macaca fascicularis monkeys (6 males and 3 females) at doses of 16 mg/kg body weight, three times a month for two years. Colon cancer was detected in two male monkeys after total DMH doses of 1080 and 3696 mg (528 and 400 mg/kg body wt., respectively). A uterine tumor was induced in one female monkey which received 3648 mg of DMH (608 mg/kg body wt.). Latent periods of tumor development were 34, 47 and 55 weeks, respectively. Histologically, the colon tumors had the structure of adenocarcinoma in both cases and the uterine tumor was diagnosed as fibromyoma.

Low-frequency electromagnetic radiation enhances the induction of rat mammary tumors by nitrosomethyl urea.

Low-frequency electromagnetic fields enhance the induction of mammary gland tumors in rats using nitrosomethyl urea. The incidence of tumors depended on the duration of exposure to static (dc) and variable (ac) magnetic fields. Variable magnetic fields induced mammary gland cancer much more frequently than static ones. Apart from increasing the incidence of mammary gland tumors, household low-frequency electromagnetic fields reduced the mean latent period of tumor development and led to predominance of malignant tumors in the exposed animals as compared to controls. Mammary gland tumors developed rarely under the effect of static or variable magnetic fields per se, without preliminary administration of a carcinogen. Household low-frequency electromagnetic fields may potentially present an oncogenic hazard for animals and humans.

Morphology of experimental tumors of the sympathetic nervous system.

The morphology of experimental tumors of the sympathetic nervous system in rabbits and hamsters induced by administration of nitrose compounds and the use of modifying factors were studied. The tumors were localized in the mediastinum, retroperitoneal space, adrenals and kidneys. A predominant involvement of the female animals was observed. Histological, histochemical and electron microscopic studies of 33 tumors of the sympathetic nervous system were carried out. By their degree of maturity the tumors were classified as ganglioneuromas, ganglioneuroblastomas and neuroblastomas. By their structure the experimental tumors were similar to the analogous neoplasias of man.

Induction of renal tumors in cynomolgus monkeys (Macaca fascicularis) by prenatal exposure to 1,2-dimethylhydrazine.

Nephroblastomas were induced at an early age in two of six cynomolgus monkeys by prenatal exposure to 1,2-dimethylhydrazine. In one, the tumor of the right kidney had metastasized into the lower lobes of the lungs. By their histologic structure, development, and clinical course, the induced nephroblastomas were analogous to the Wilms' tumors often found in children.

An overview of the world literature on spontaneous tumors in nonhuman primates.

A review of the world literature has revealed a total of 783 spontaneous neoplasms that have occurred in nonhuman primates, all similar to tumors in human beings. Carcinomas were the most frequently reported. Neoplasms occurred most frequently in older animals as they generally do in man. There were more reports on neoplasms in baboons and macaques than in other species. The digestive system was more commonly affected than were other organ systems.

An experimental model for peripheral nerve tumours in monkeys.

The induction of tumours of the peripheral nerves in Macaca mulatta has been accomplished by injections of the carcinogen methylnitrosourea in combination with organospecific immunization with antigens from the homologous tissue (sciatic nerve). The histology and biological peculiarities of the tumours are similar to those seen in man.