Expression of CD15 in tumours of the nervous system

The expression of the CD15 epitope was investigated by immunohistochemistry, western blotting and immuno-thin-layer chromatography on a large series of human nervous system tumours and ethylnitrosourea-induced rat gliomas. Our results show that CD15 is expressed as a glycoprotein- or glycolipid-associated epitope in normal human and rat brain. In contrast, immunoreactivity for CD15 was absent in tumour cells of experimental rat gliomas. In human tumours we found a more complex expression pattern. While intra- and perivascular granulocytes as well as macrophages in necrotic areas of anaplastic tumours were always strongly CD15-positive, immunoreactive tumour cells were detectable only in a fraction of low-grade gliomas. Anaplastic gliomas and glioblastomas consistently did not express the epitope on their tumour cells. In addition to individual low-grade gliomas, we found CD15-positive cases among metastatic carcinomas, craniopharyngeomas, meningiomas, germinomas and malignant melanomas. Our results suggest that immunohistochemistry for CD15 is potentially useful in diagnostic neuropathology as a marker for granulocytes in paraffin sections, as a supplementary tool for the histopathological grading of gliomas, and as an aid for differentiation between anaplastic glioma cells and non-neoplastic glia. Furthermore, it can be speculated that the lack of CD15 expression on anaplastic glioma cells may potentially be responsible for some of their characteristics--such as altered cellular interaction and loss of contact inhibition.

[Angiogenesis induced by rat glioma cells in vitro]

Angiogenesis induced by rat glioma cells was examined in vitro using a double chamber co-culture system. Cultured microvascular endothelial cells from Fisher 344 rat brain, rat C6 glioma cells and rat T9 gliosarcoma cells were used for this study. Endothelial cells, cultured on type I collagen, formed capillary-like structures. In the co-culture system, C6 glioma cells promoted this formation. On the other hand T9 gliosarcoma cells had no effect on it. The supernatants of C6 glioma cells and T9 gliosarcoma cells suppressed the proliferation of the endothelial cells. C6 glioma cells probably produce and release soluble factors promoting angiogenesis. The proliferation of endothelial cells is thus suppressed while angiogenesis is made more intense. This in-vitro model is useful to elucidate the mechanism of tumor angiogenesis and to evaluate the promoting and inhibiting factors of angiogenesis.

Immunohistochemical observations on rat radial glia: relationship with the origin of ethylnitrosourea-induced tumors

Gliomas induced in the rat by transplacental administration of ethylnitrosourea (ENU) are intensely immunoreactive for vimentin and scarcely for glial fibrillary acidic protein (GFAP). Since tumoral transformation takes place during the late fetal and early postnatal period, the sequential expression of the two glial antigens has been investigated in this age period in ENU-treated and control rats. Immunohistochemical and immunoelectron microscopical methods have been employed. Vimentin was widely expressed starting from embryonal day 14 (E 14) in the processes of radial glia; as long as radial glia was present, vimentin decorated it. GFAP was, at earliest, observed at E 20 and expressed by glial cells with a stellate, i.e., mature shape. No GFAP-positive radial process was observed. No difference was found between ENU-treated and control rats. Since ENU is most effective in producing tumors when administered at the 16-17th day of fetal life, vimentin-positive radial glia is a candidate target of ENU. The similarity of intermediate filament pattern between radial glia in the late fetal life and tumors induced by transplacental ENU suggests that radial glia might be the cell of origin.

Immunohistochemical localization of gangliosides in ENU-induced rat glioma

Biochemical studies have indicated that the structurally simple gangliosides, including GD3 and GM3, are major glycolipid components of glioma tissues. In order to clarify the localization of the gangliosides in ethylnitrosourea-induced rat glioma, an immunohistochemical study was performed using antibodies against GM1, GM3, and GD3. The results obtained in normal fetus, newborn, and adult rat brain, and also in human glioma, were compared. In fetal and newborn rat brain, GD3 was present mainly in the neuroepithelial cell surface of the matrix and subependymal layers of the ventricular wall, but GM3 and GM1 were not detected. In adult rat brain, GD3-positive cells were absent, or present in diminished number, and GM1 was found chiefly in the neuropil of the cerebral cortex. Most of the rat glioma cells were positive for GD3, but not for GM1. It was demonstrated that the ganglioside composition of glioma cells was similar to that of immature neuroectodermal cells in fetal and newborn rat brain. Furthermore, the number of GD3-positive oligodendroglioma cells increased with tumor growth. In anaplastic gliomas and gross oligodendrogliomas, most tumor cells expressed not only GD3 but also GM3. These results suggest that GD3 is a marker of proliferating neuroectodermal cells, and that activity of the key enzymes in ganglioside synthesis alters with tumor growth and anaplastic change.

A subdomain in the transmembrane domain is necessary for p185neu* activation

The neu proto-oncogene encodes a protein highly homologous to the epidermal growth factor receptor. The neu protein (p185) has a molecular weight of 185,000 Daltons and, like the EGF receptor, possesses tyrosine kinase activity. neu is activated in chemically induced rat neuro/glioblastomas by substitution of valine 664 with glutamic acid within the transmembrane domain. The activated neu* protein (p185*) has an elevated tyrosine kinase activity and a higher propensity to dimerize, but the mechanism of this activation is still unknown. We have used site-directed mutagenesis to explore the role of specific amino acids within the transmembrane domain in this activation. We found that the lateral position and rotational orientation of the glutamic acid in the transmembrane domain does not correlate with transformation. However, the primary structure in the vicinity of Glu664 plays a significant role in this activation. Our results suggest that the Glu664 activation involves highly specific interactions in the transmembrane domain of p185.

Brain cancer and farming in western Canada

A cohort study of the mortality experience (1971-1987) of male Canadian prairie farmers has been conducted. This involved linking the records of 156,242 male Alberta, Saskatchewan and Manitoba farmers identified on the 1971 Census of Agriculture and the corresponding Census of Population to mortality records. Exposure indices for individual farm operators were derived from 1971 Census of Agriculture records. Cancer histologies for brain cancer cases were obtained from the Canadian National Cancer Incidence Database and from Provincial Cancer Registries. A statistically significant association was noted between risk of dying of glioblastomas and increasing fuel/oil expenditures (test for trend p = 0.03, top quartile relative risk = 2.11, 95% confidence interval = 0.89-5.01). No significant association was found between brain cancer and either education or mother tongue. However, low income was associated with a significantly reduced risk of brain cancer mortality.

[Mercury in the dental office. Risk evaluation of the occupational environment in dental care]

This article gives a toxicological risk analysis of occupational diseases in dentistry that are related to chronic exposure to inorganic mercury, especially metallic mercury vapour. Studies have indicated that dental work involving mercury may be an occupational hazard with respect to reproductive processes, glioblastoma (brain cancer), renal function changes, allergies and immunotoxicological effects. The correlation of chronic exposure to mercury in dentistry to the health situation of dental workers' health situation needs to be further studied.

Exposure to barbiturates in utero and during childhood risk of intracranial and spinal cord tumors

Barbiturate exposure during childhood was assessed from medical records of 237 children with intracranial and spinal cord tumors and 474 matched controls in a prepaid health plan. In utero exposure was also examined in a subset of 86 "cases" and 172 controls whose mothers were health plan members during pregnancy. No association of in utero exposure to barbiturates was found [odds ratio (O.R.) = 0.96, 95% confidence interval (C.I.) = 0.47, 1.94]. An association was noted for barbiturate use during childhood (O.R. = 1.80, 95% C.I. = 1.18, 2.74) but was reduced (O.R. = 1.41, 95% C.I. = 0.89, 2.21) when history of epilepsy was taken into account and was no longer significant. An apparent dose-response effect disappeared after adjustment for a history of epilepsy. Although barbiturate use for epilepsy due to preexisting brain tumors clearly explains some of the observed association, the small, residual risk prevents us from ruling out a possible carcinogenic effect of barbiturates. Further study of cohorts of adult as well as childhood users of barbiturates and other anticonvulsants is recommended.

Carcinogenicity study of doxefazepam administered in the diet to Sprague-Dawley rats

Groups of 50 male and 50 female Sprague-Dawley rats were given food containing sufficient doxefazepam, a benzodiazepine derivative, to ensure intakes of 0, 3, 10, or 30 mg/kg/day. These dosages respectively correspond to 2, 20, and 60 times the mean daily hypnotic dose level of an adult man. Rats were treated for 104 weeks and then euthanized. An extensive autopsy was performed on those animals that died intercurrently and on euthanized animals. The chronic administration of doxefazepam did not influence the survival of the rats. No treatment-related changes in clinical signs and body weight gains occurred and malignant tumor rates were similar in controls and treated animals. A significant linear trend in the incidence of hepatocellular neoplasms, primarily benign, was observed in the female treated groups. This higher incidence was not associated to a higher occurrence of focal hyperplasia or other preneoplastic lesions in treated rats. The brain, a target organ for the pharmacological activity of doxefazepam, was carefully examined to search for microscopic foci of proliferative cells. A total of 12 and 6 malignant gliomas were observed in male and female rats, respectively; only two were noticed at autopsy. These tumors were mainly of the oligodendroglioma type commonly found in aged rats. Their incidence was slightly higher in treated rats, but results were not of statistical significance. The overall evaluation of the present study indicates that doxefazepam is noncarcinogenic in rats. However, the increase in liver adenomas found here as well as in previous bioassays with similar drugs and the lack of reliable historical data on the incidence of brain tumors in benzodiazepine-treated rodents suggest that additional experimental and epidemiological studies should be undertaken to exhaustively assess the toxic potential of this widely used class of drugs.

[Synthesis and animal experiments of ethylnitrosourea]

Ethylnitrosourea (ENU) was synthesized with raw materials such as ethylamine and sodium nitrite. The product was a yellowish powder. Its melting point, solubility and infrared absorption spectrum coincided with those reported in the literature. The result form elementary analysis for the product was almost the same as the theoretical value. The product was applied to rats by various methods. It was found that ENU was a cancerogenic compound, especially to the nervous system. More details about the animal experiments will be published in some other papers.

[Experimental brain tumor in adult mongrel cat]

Small animal models such as the rat have serious limitations for multiple human scale instrumentation, surgical manipulations, and computerized tomographic (CT) evaluations, so that large animal models are required for the study using them. Although brain tumors induced with Rous sarcoma virus in neonatal beagle or adult monkey had been reported, these animals are very expensive ones for tumor research. A major drawback of virally induced brain tumor model is, moreover, the need for specialized viral facilities and safety precautions for laboratory personnel. In this paper, a cat glioma model implanted with C6 glioma cells derived from rats injected with N-nitrosomethylurea is reported. For an implantation dose of 5 x 10(5) cells/50 microliters, C6 glioma cells were suspended in modified Eagle medium supplemented with 10% fetal bovine serum and 0.5% agar. Twenty adult mongrel cats were injected with 5 x 10(5) C6 glioma cells intracerebrally. Implanted cats had brain tumors of about 10 mm in diameter with a yield of 80%. The mean survival was about 3 weeks after implantation. Tumors developed as spheroidal, hemorrhagic masses with central areas of necrosis and peripheral edema. They were located within the parenchyma of the implanted region. This tumor possessed many of the histological and radiological characteristics of human glioblastoma such as the following: Areas of hemorrhage and necrosis surrounded by pseudopallisading were observed within the tumor consisting of spindle-shaped cells with pleomorphic nuclei. A mass lesion with ring or garland-like enhancement surrounded by brain edema was shown on the CT scans.(ABSTRACT TRUNCATED AT 250 WORDS)

Radioresistance of rat glioma cell lines cultured as multicellular spheroids. Correlation with electrical cell-to-cell-coupling

Two chemically induced rat glioblastomas, RG2 and F98, were cultured as monolayers and as multicellular spheroids and subjected to Co-gamma-irradiation. In parallel, intercellular communication between cells was determined as electrical coupling between neighbouring cells using micro-electrode techniques. A third glioblastoma with known radiobiological response (9L) was assayed with respect to intercellular communication and included into this analysis. Electrical coupling was low for RG2, intermediate for F98, and high for 9L. Radioresistance of spheroids, as expressed in terms of the mean inactivation dose computed from the survival curves increased in the same direction (RG2: 2.4 Gy; F98: 5.1 Gy; 9L: 6.5 Gy). A comparison of these parameters demonstrates a correlation between solid tumor radioresistance and gap-junctional cell-to-cell communication, at least for the class of glioblastomas analysed in this study.

Immunohistochemical characterization of rat central and peripheral nerve tumors induced by ethylnitrosourea

Ethylnitrosourea-induced central and peripheral nerve tumors in Sprague-Dawley rats were tested for GFAP (Glial Fibrillary Acidic Protein), S-100 protein, NSE (Neuron Specific Enolase) and Anti-Leu 7 (HNK-1) immunoreactivity utilizing the ABC method (avidin-biotin-complex) for GFAP, S-100 protein and NSE, and the PAP method (peroxidase-antiperoxidase) for Anti-Leu 7. Peripheral nerve neurinomas were consistently positive for S-100 protein and consistently negative for GFAP and Anti-Leu 7. Neurinomas would occasionally exhibit positive staining for NSE (2 of 55 tumors). The staining intensity for S-100 protein varied from strongly positive in differentiated neurinomas to weakly positive in anaplastic tumors. Neoplastic and reactive astrocytes exhibited positive staining for both S-100 protein and GFAP. Variation in the GFAP staining intensity of glial tumors correlated with the degree of differentiation as anaplastic tumors did not stain with the same intensity as their more differentiated counterparts. Oligodendrogliomas exhibited occasional immunoreactivity to S-100 protein (3 of 36 tumors). NSE reactivity in oligodendrogliomas was rarely observed (1 tumor in 36) and immunoreactivity against GFAP or Anti-Leu 7 was consistently absent. Anti-Leu 7 and NSE proved to be of little value in the classification of ENU-induced neural tumors.

[Differences in microvasculature between ethylnitrosourea-induced brain tumor and transplanted 9L cell brain tumor in the rat]

The microvasculature of ethylnitrosourea (ENU)-induced brain tumors and transplanted 9L cell brain tumors were studied in ultrathin sections and by the freeze fracture replica method. The vessels in ENU-induced tumors were similar to human glioma vessels in that they had endothelial tight junctions and increased pinocytotic vesicles. In the 9L cell tumors, the vessels lacked endothelial tight junctions and had fenestrated endothelium. Macroscopically, Evans blue dye penetrated the 9L cell tumors but not the ENU-induced tumors. Judging from the ultrastructure of the microvessels, the ENU-induced tumor appears more suitable as a human glioma model.

Glomeruloid blood vessels in ethylnitrosourea-induced rat gliomas. Histological and immunohistochemical studies

Glomeruloid blood vessels (GBVs), a characteristic histological feature of most human malignant gliomas, were recognized with high incidence in autochthonous rat gliomas induced by transplacental administration of ethylnitrosourea. To evaluate some of the biological properties of these GBVs, we carried out a study using histological methods and immunohistochemical staining for glial fibrillary acidic protein, factor VIII-related antigen (VIII Ag) and bromodeoxyuridine (BrdUrd). Of 22 animals with large, massively growing gliomas in the CNS, GBVs including conglomerate aggregations of small blood vessels with endothelial hyperplasia and strong VIII Ag expression were observed in 13 large gliomas histologically consisting of primitive neuroepithelial neoplasms (PNN; so called ependymoma) and mixed-type gliomas in combination with astrocytoma and PNN or anaplastic astrocytoma. The anaplastic gliomas in our series were devoid of GBVs. These findings indicate that GBV formation takes place in a histological variety of experimental gliomas. Furthermore, the GBVs were frequently associated with the vasculo-mesenchymal stroma in the parent gliomas, suggesting an intimate relationship with the morphogenesis of GBVs. In addition, it was shown that the GBVs had a higher BrdUrd-labelling index than that of other blood vessels in gliomas and also that of neoplastic cells in most parent gliomas, except for anaplastic gliomas. Based on these results, the possible mechanism of GBV morphogenesis is discussed with regard to the roles of macromolecules in the induction and regulation of GBVs.

Effect of chronic stress on ENU-induced tumors

The relation of stress to cancer is the subject of considerable controversy. We studied the possible influence of chronic stress on the time of development and frequency of tumors induced in rats after a single exposure to ethylnitrosourea during prenatal life. Time of development, localization, incidence, type, and size of tumors were similar in stressed rats and in controls. Our results in this paradigm do not support the hypothesis that chronic stress exerts a potentiating effect on carcinogenesis.

Chemical induction of brain tumors in rats by nitrosoureas: molecular biology and neuropathology

Nitrosourea-induced rat brain tumors are among the best investigated experimental systems for neuropathological, biochemical, diagnostic and therapeutic research in neurooncology. This review summarizes data concerning molecular biology, neuropathology, in vitro studies, transplantation models and antigen expression of experimental gliomas in inbred rat strains. Systemic application of nitroso-compounds, i.e., ENU and MNU, leads to the alkylation of DNA bases, which, due to a specific repair deficiency, persist in the nervous system remarkably longer than in other organs. The hypothesis is that alkylated bases cause base-mispairing and point mutations followed by uncontrolled expression of oncogenes and growth factor receptors, resulting in permanent cell proliferation. Thus, nitrosoureas are considered to be biological hazards, especially as potent endogenous and exogenous neurotoxins. Neuropathology and growth characteristics of these experimental tumors are comparable to human malignant gliomas. Similar to the human WHO grade III and IV tumors, they reveal cellular pleomorphism, elevated mitotic activity, proliferation of blood vessels, blood-brain barrier disturbances, necrosis and invasiveness. Nitrosourea-induced brain tumors have been used in investigations concerning glioma growth and regression, brain edema, glioma immunology, metabolism, regional biochemistry, and experimental therapy. The studies included conventional morphology, immunohistochemistry, -cytochemistry and -electronmicroscopy, morphometry, cell culture, hybridoma technology, tumor transplantation and regional imaging by autoradiography, bioluminescence, magnetic resonance and immunoscintigraphy.

A sequential ultrastructural and histoautoradiographic study of early neoplastic lesions in ethylnitrosourea-induced rat glioma

A sequential study of the early stage of development of ethylnitrosourea (ENU)-induced glioma in the rat was performed by electron microscopy and [3H]thymidine histoautoradiography. Hyperplasia, the earliest neoplastic change that was detectable morphologically, consisted of a few or several immature oligodendroglia-like cells which were connected with one another or with preexisting neural tissue by junctional apparatus, and showed no reactive changes in the astrocytes or microglia. The labelling index of hyperplastic cells was 2.6%. Foci of early neoplastic proliferation (ENP) showed mild destructive changes in the neighboring neural tissue, and their major constituent cells had characteristics of immature oligodendroglias. The labelling index of cells showing ENP was 3.3%. The intercellular spaces exhibited slight enlargement with accumulation of extracellular matrix and a decrease in the number of junctional apparatus on the neoplastic cells. Microtumors showed apparent destruction of the preexisting neural tissue to form a tumor mass with an increase in the extracellular matrix. Constituent cells of the microtumors were similar to those of the ENP, although reactive astrocytes and microglias occurred more frequently. The labelling index was 9.6% in the central area of microtumors and 5.3% in the peripheral area. These findings suggest that in the initial or very early stages of glial cell neoplastic proliferation, it is necessary for the neoplastic cells to maintain contact with the neurons for metabolic purposes, and that after losing contact, these cells can proliferate autonomously with the accumulation of extracellular matrix.

Phenobarbital lacks promoting activity for neurogenic tumors in F344 rats transplacentally exposed to ethylnitrosourea

A chronic rodent study in F344 rats was conducted to investigate the promoting ability of phenobarbital (PB) on neurogenic tumors initiated by transplacental administration of ethylnitrosourea (ENU). Pregnant F344 rats were given a single intravenous dose of 3.5 mg ENU/kg or vehicle on the twentieth day of gestation. A total of 192 male offspring were divided into four groups: ENU-PB, ENU-control, PB-control, and control-control. Rats in ENU-PB and PB-control groups received 0.05% PB in their drinking water from four to 78 weeks of age. Nervous system tumors were induced only in animals exposed to ENU. The difference in the incidence of neuroectodermal tumors in rats that were ENU initiated only (13/37; 35%) compared to the incidence in rats that were initiated and given PB (13/57; 23%) was not statistically significant (p greater than 0.05). ENU-control and ENU-PB treatment groups exhibited no differences in tumor multiplicity or tumor latency. These results demonstrate that PB lacks promoting activity for neurogenic tumors in F344 male rats transplacentally exposed to ENU.

A comparison of the effect of several factors on the plasminogen activator activity of cloned lines from an ethylnitrosourea-induced glioma and from normal tissue

Cells from gliomas induced by N-ethyl-N-nitrosourea have a high basal level of plasminogen activator activity compared with cells from normal tissue. Plasminogen activator activity is known to be affected by many substances but whether inhibition or stimulation occurs depends on the cell and agent involved. It is not clear whether tumour and control cells from the same type of tissue respond similarly. A comparison has been made of the effect of several factors on both cell associated and secreted enzyme activity of cloned lines from a glioma and normal tissue. The effect of two cAMP elevating compounds was stimulatory while that of the steroid, dexamethasone, was generally inhibitory for both cells. However, the polypeptide hormone, epidermal growth factor, had a differential effect. It caused an increase in secreted enzyme activity in the tumour line but had no such effect on the control clone. The precise mechanism by which this occurs is unknown. Co-operative effects of the enzyme and growth hormone could result in more aggressive behaviour of the tumour cells.

Expression of vimentin and glial fibrillary acidic protein in ethylnitrosourea-induced rat gliomas and glioma cell lines

The expression of glial fibrillary acidic protein (GFAP) and vimentin was investigated immunohistochemically in 104 experimental gliomas induced by transplancental application of ethylnitrosourea (ENU) in CDF rats. Immunoreactivity for vimentin was prominent in many astrocytic tumor cells and especially in small glioma cells forming anaplastic medulloblastoma-like foci in many tumors. The majority of tumor cells in oligodendroglial tumors were vimentin negative, except for some of the large polymorphous oligodendrogliomas which contained intermingled vimentin positive glioma cells. GFAP immunoreactivity was detectable only in a low fraction of tumor astrocytes and in a few exceptional cases some oligodendroglial tumor cells stained positive. Immunohistochemistry with antibodies against neurofilaments and cytokeratins revealed no staining in tumor cells of ENU-induced gliomas, while all oligodendrogliomatous tumors stained positive for HNK-1. Immunocytological and immunoblot investigations of the two rat glioma cell clones RG2 and F98, which are both derived from ENU-induced gliomas, showed a prominent expression of vimentin in monolayer cultures and in syngeneic intracerebral transplantation tumors. F98 additionally demonstrated a fraction of GFAP positive cells especially in confluent cultures and in intracerebral tumors. RG2, on the other hand, exhibited virtually no GFAP immunoreactivity in culture but showed individual GFAP positive tumor cells in intracerebral tumors. Our results revealed a more precise picture of the cellular differentiation in ENU-induced rat gliomas and in two widely used glioma cell lines. They underline the heterogeneity of experimental rat gliomas which may comprise cells at different stages of differentiation towards oligodendroglial or astroglial phenotype.

Gliomas and exposure to wood preservatives

A case-referent study was undertaken to look for occupational risk factors among patients with glioma treated in a neurological hospital in Paris between 1975 and 1984. In the study group were 125 men with gliomas (aged less than or equal to 65) and 238 patients (also less than or equal to 65) admitted for non-neoplastic, non-malformative vascular diseases in the same department during the same period constituting the reference group. All diagnoses were confirmed by tomodensitometry. Information on occupational history was obtained from a postal questionnaire and from medical records. Comparison of cases and referents showed a significant excess risk among teachers (OR = 4.1) and a raised risk among wood workers (OR = 1.6). Four of nine cases of glioma who had been employed as wood workers reported that a colleague had suffered from glioma (those reports were confirmed by hospital records). None were reported among 11 referent wood workers. Using a complementary questionnaire on wood work, exposure assessment to wood preservatives and solvents showed that frequent exposure to organochlorine wood preservatives and to organic solvents occurred more often among cases than referent wood workers (p less than 0.10).

A case-control study of brain gliomas and occupational exposure to chemical carcinogens: the risk to farmers

During 1983 and 1984, 240 newly diagnosed cases of brain glioma and 742 controls (465 non-glioma nervous system tumors and 277 patients with other neurologic diseases) were recruited and interviewed in the neurologic and neurosurgical departments of two hospitals in Milan, Italy. The occupational histories of cases and controls were compared, and relative risk estimates, adjusted for sex, age, residence, and socioeconomic status, were computed using the Mantel-Haenszel method. A statistically significant risk increase was found for farmers (relative risk (RR) = 1.6, p = 0.0025). This risk increase was attributable to those farmers who reported the use of chemicals (insecticides or fungicides, herbicides, and fertilizers). Among the three groups of investigated agrochemicals, only the use of insecticides or fungicides was associated with a significant increase in relative risk (RR = 2.0, p = 0.006). Many farmers exposed to fungicides reported the use of commercial compounds of copper sulfate. Some of these compounds contain methyl urea, which has a specific carcinogenic effect on the nervous system in animals. These data suggest that the occupational exposure of farmers to agrochemicals might be responsible for the observed excess risk of brain glioma in farmers.

Vascular permeability and cell kinetics of ethylnitrosourea (ENU)-induced rat brain tumours

Vascular permeability and proliferative activity of ethylnitrosourea (ENU)-induced rat brain tumours were studied by intravenous injection of Evans blue dye (EB) and by bromodeoxyuridine (BrdU) uptake examinations. Tumours induced by ENU showed various histologial types, and they were oligodendrogliomas, mixed oligo-astrocytomas, mixed oligo-ependymomas, astrocytomas, anaplastic astrocytomas, polymorphic gliomas, and ependymomas. The labelling indexes (LIs: the ratio of BrdU-labelled cells to total cells) of tumour and vascular component cells in the tumour were high in anaplastic astrocytomas, polymorphic gliomas and ependymomas, but low in oligodendrogliomas. EB stained anaplastic astrocytomas, polymorphic gliomas and ependymomas deeply, but did not penetrate oligodendrogliomas. In mixed gliomas, EB staining and the LIs of tumour cells were not uniform. After intracarotid infusion of hyperosmolar mannitol into tumour-bearing rats, tumour staining with EB and the LIs of tumour cells were not increased, whereas the penetration of EB into the normal brain was drastically increased. Therefore it is not likely that the delivery of chemotherapeutic drugs to the tumour could be increased by intracarotid infusion of hyperosmolar mannitol. Our data suggest that the vascular permeability of tumour vessels is highly correlated with the high proliferative activity of tumour and its vascular cells.