RESUMEN
This article evaluates the possibility of creating a tax for urban drainage in order to make the system self-financing. Average costs of implementation and maintenance of the services were used to individualize the charges and definition of the tax. The conventional drainage system was evaluated along with a source control alternative, water detention in tanks on the lot. The magnitude of the values being charged varies in function of the impermeable surface and the density of the urban area. Preserving creeks in natural conditions and using source control approach, are all options with the advantages of lower investment and smaller burden for the users.
Asunto(s)
Impuestos , Eliminación de Residuos Líquidos/economía , Abastecimiento de Agua , Ciudades , Costos y Análisis de Costo , Humanos , Densidad de Población , Eliminación de Residuos Líquidos/métodosRESUMEN
Uroporphyrinogen I Synthase (URO-S) activity was measured in erythrocytes of female and male rats which had received diethylnitrosamine (DENA) as an inducer of hepatic tumors. Twenty-two weeks after the last dose of the carcinogen, the rats showed statistically significant increases in the URO-S activity. Differences in the body weight, erythrocyte porphyrin content or the hematocrit between treated and control rats were not found. Fifty percent of female rats and thirty percent of male rats treated with DENA were found to have hepatic tumors but there was no correlation between blood URO-S activity and tumoral development in spite of the increase in URO-S activity observed in DENA treated rats. This was observed both in male and female rats.
Asunto(s)
Carcinoma Hepatocelular/enzimología , Dietilnitrosamina/uso terapéutico , Eritrocitos/metabolismo , Hidroximetilbilano Sintasa/metabolismo , Neoplasias Hepáticas/enzimología , Animales , Femenino , Hidroximetilbilano Sintasa/sangre , Masculino , RatasRESUMEN
Se midió la actividad de Uroporfirinógeno I sintasa (URO-S) en eritrocitos de ratas hembras y machos que habían recibido dietilnitrosamina (DENA) como inductor de tumores hepáticos. Veintidós semanas después de la última dosis del carcinógeno, las ratas mostraron incrementos estadísticamente, significativos en la actividad de URO-S. No se encontraron diferencias en el peso de los animales, en el contenido de porfirinas eritrocitarias ni en el hematocrito entre las ratas tratadas y los animales control. Se observó que el cincuenta por ciento de las ratas hembras y el treinta por ciento de las ratas machos tratadas con DENA habían desarrollado tumores hepáticos pero no hubo correlación, ni en machos ni en hembras, entre la actividad de URO-S y el desarrollo tumoral a pesar del incremento obtenido en los animales tratados con DENA en la actividad de esta enzima
Asunto(s)
Animales , Masculino , Femenino , Ratas , Carcinoma Hepatocelular/inducido químicamente , Dietilnitrosamina/uso terapéutico , Hidroximetilbilano Sintasa/metabolismo , Neoplasias Hepáticas/inducido químicamente , Hidroximetilbilano Sintasa/sangreRESUMEN
Uroporphyrinogen I Synthase (URO-S) activity was measured in erythrocytes of female and male rats which had received diethylnitrosamine (DENA) as an inducer of hepatic tumors. Twenty-two weeks after the last dose of the carcinogen, the rats showed statistically significant increases in the URO-S activity. Differences in the body weight, erythrocyte porphyrin content or the hematocrit between treated and control rats were not found. Fifty percent of female rats and thirty percent of male rats treated with DENA were found to have hepatic tumors but there was no correlation between blood URO-S activity and tumoral development in spite of the increase in URO-S activity observed in DENA treated rats. This was observed both in male and female rats.
RESUMEN
Se midió la actividad de Uroporfirinógeno I sintasa (URO-S) en eritrocitos de ratas hembras y machos que habían recibido dietilnitrosamina (DENA) como inductor de tumores hepáticos. Veintidós semanas después de la última dosis del carcinógeno, las ratas mostraron incrementos estadísticamente, significativos en la actividad de URO-S. No se encontraron diferencias en el peso de los animales, en el contenido de porfirinas eritrocitarias ni en el hematocrito entre las ratas tratadas y los animales control. Se observó que el cincuenta por ciento de las ratas hembras y el treinta por ciento de las ratas machos tratadas con DENA habían desarrollado tumores hepáticos pero no hubo correlación, ni en machos ni en hembras, entre la actividad de URO-S y el desarrollo tumoral a pesar del incremento obtenido en los animales tratados con DENA en la actividad de esta enzima (AU)
Asunto(s)
Animales , Masculino , Femenino , Ratas , Neoplasias Hepáticas/inducido químicamente , Carcinoma Hepatocelular/inducido químicamente , Dietilnitrosamina/uso terapéutico , Hidroximetilbilano Sintasa/metabolismo , Hidroximetilbilano Sintasa/sangreRESUMEN
Female F344 rats received an i.p. injection of iron-dextran (600 mg Fe/kg) and then after 1 week were fed a diet containing 0.02% hexachlorobenzene (HCB) for up to 65 weeks. All rats (8/8) which received HCB after iron overload developed multiple hepatic nodules whereas only 3/8 rats administered HCB alone had nodules (average of one per positive liver). These hyperplastic regions were depleted of iron and were often positive for gamma-glutamyl transpeptidase (GGT) and glutathione S-transferase P (GST-P). Telangiectasis and peliosis were prominent features in the lesions. Short-term experiments (5-15 weeks of iron/HCB treatments) showed that GGT and GST-P were induced early in the neoplastic process but not in discrete focal areas. Iron alone also caused some induction of these enzymes. Some cells with induced GST-P in either short or long term experiments also stained positively for this enzyme in the nucleus. Studies of cytochrome P450 mediated activities showed that at 5 and 15 weeks HCB had induced EROD (an estimate of CYP1A1), PROD (CYP2B1 activity) and BROD activities (CYP2B1 but also other isoenzymes). Under the influence of iron overload EROD was significantly depressed from HCB alone, but not the others or cytochrome P450 reductase. Cytosolic glutathione S-transferase activities were also induced by HCB, but, unlike microsomal EROD, preloading with iron enhanced the effects. In contrast, although cytosolic diaphorase activity was induced by HCB, this response was depressed in combination with iron. Glutathione peroxidase (with H2O2 as substrate) was depressed by both iron and HCB. Clearly, iron overload potentiates the neoplastic process induced by HCB in rats, with both enhancing and depressing effects on various enzyme activities induced by this chemical.
Asunto(s)
Carcinógenos/toxicidad , Hexaclorobenceno/toxicidad , Hierro/toxicidad , Neoplasias Hepáticas/inducido químicamente , Animales , Cocarcinogénesis , Sistema Enzimático del Citocromo P-450/biosíntesis , Inducción Enzimática , Femenino , Glutatión Transferasa/biosíntesis , Glutatión Transferasa/metabolismo , Hierro/administración & dosificación , Hígado/patología , Neoplasias Hepáticas/enzimología , Neoplasias Hepáticas/patología , Porfirias/inducido químicamente , Ratas , Ratas Endogámicas F344RESUMEN
The present study was undertaken to explore the effect of the presence of hepatic tumors induced by diethylinitrosamine (DENA) on the metabolic heme pathway, and to assess whether these tumors can modify the response of rats to the porphyrinogenic drug hexachlorobenzene (HCB) and whether the above mentioned effects occur to a greater extent in females than males. The results obtained showed that: a) Females were more susceptible to the hepatocarcinogenicity of DENA than males. b) Female normal and DENA treated rats were more susceptible than male rats to the porphyrinogenicity of HCB. c) The presence of hepatic DENA induced tumors could diminish basal hepatic ferrochelatase activity. d) Hepatic tumors could modify the response of animals to a porphyrinogenic drug such as HCB. Thus, both female and male DENA/HBC rats accumulated more porphyrins and showed a lower delta-aminolevulinate synthase and uroporphyrinogen I synthase induction than HCB rats. e) The heme pathway was functional in DENA induced tumors in both male and female rats but they were little affected by HCB.
Asunto(s)
Hemo/metabolismo , Neoplasias Hepáticas Experimentales/enzimología , Porfirias/enzimología , Porfirinas/metabolismo , Caracteres Sexuales , 5-Aminolevulinato Sintetasa/metabolismo , Animales , Carboxiliasas , Sistema Enzimático del Citocromo P-450/metabolismo , Dietilnitrosamina , Femenino , Ferroquelatasa/metabolismo , Hexaclorobenceno , Hidroximetilbilano Sintasa/metabolismo , Neoplasias Hepáticas Experimentales/inducido químicamente , Neoplasias Hepáticas Experimentales/patología , Masculino , Porfirias/inducido químicamente , RatasRESUMEN
The response of female BDVI rats bearing diethylnitrosamine(DENA)-induced hepatic tumors to the porphyrinogenic action of hexachlorobenzene (HCB) was studied. (1) The heme pathway operates in these tumors but they were less affected by HCB than the liver. (2) Tumors did not accumulate porphyrins although the surrounding liver accumulated more porphyrins than livers treated with HCB. (3) DENA/HCB livers which developed a well defined tumor showed slightly less porphyrinogen carboxylyase inhibition and delta-aminolaevulinate synthase induction than HCB rats. (4) The results of the present work suggest that endogenously formed porphyrins would be unable to be accumulated by DENA-induced tumors when the tumoral development precedes the onset of the porphyria.
Asunto(s)
Carcinoma Hepatocelular/complicaciones , Dietilnitrosamina/farmacología , Hexaclorobenceno/farmacología , Neoplasias Hepáticas/complicaciones , Porfirias/metabolismo , 5-Aminolevulinato Sintetasa/metabolismo , Ácido Aminolevulínico/orina , Animales , Carcinoma Hepatocelular/inducido químicamente , Carcinoma Hepatocelular/metabolismo , Sistema Enzimático del Citocromo P-450/metabolismo , Femenino , Ferroquelatasa/metabolismo , Hígado/metabolismo , Neoplasias Hepáticas/inducido químicamente , Neoplasias Hepáticas/metabolismo , Porfobilinógeno/orina , Porfirias/etiología , Porfirinas/metabolismo , RatasRESUMEN
Groups of rats, either dosed with N-nitrosodiethylamine (NDEA) for 10 weeks (from the age of 7 to 17 weeks) or untreated, were fed diets containing either 2% (low fat, LF) or 30% polyunsaturated fat (high fat, HF) on an equicaloric basis from 5 weeks until rats were 43 weeks old. Biochemical parameters were measured during and at the end of the experiment in various organs, blood, urine and exhaled air, for correlation with the presence or absence of tumors. The HF diet tended to increase the number of hepatic tumors induced by NDEA, while the number of extrahepatic tumors was higher in rats fed on the LF diet; also the overall tumor incidence was higher in the LF group. In the HF/NDEA group, only two benign extrahepatic tumors were found. Plasma total and free cholesterol and triglyceride concentrations were lower in the HF than the LF group without NDEA treatment. In animals bearing liver and/or extrahepatic tumors all plasma lipid concentrations were lower than in tumor-free animals. Only minor or no changes were detected in blood catalase activity, malondialdehyde level, reduced glutathione (GSH) level or GSH-related enzymes and excretion of thioethers in the urine due to dietary modulation or NDEA. Changes in the liver that were associated with the HF diet were: (i) increased amounts of some polyunsaturated fatty acids and of total phospholipids in liver microsomes; (ii) an enhanced level of lipid peroxidation in liver; (iii) a decrease in liver glutathione levels during NDEA treatment, with a simultaneous adaptive increase in superoxide dismutase levels, and a decrease in renal glutathione levels in both treated and untreated groups; (iv) enhanced microsomal induction of aminopyrine N-demethylase and epoxide hydrolase activities by NDEA, and (v) decreased hexose monophosphate shunt (HMS) activity. All mono-oxygenase activities were lower, and the activities of epoxide hydrolase, UDP-glucuronosyltransferase and HMS were higher, in liver tumors than in non-tumorous liver of similarly-treated rats. Neither diet nor NDEA had a major effect on drug-metabolizing enzyme activities in lung and kidney. HF diet significantly increased ethane exhalation (an indicator of the whole-body pro-oxidant state) over those on the LF diet: in rats on either diet, it was further increased when NDEA was given. Ethane exhalation was still elevated 30 weeks after the cessation of NDEA treatment. Our results suggest an association between the observed changes in biochemical parameters, notably oxidative stress, due to dietary modulation and the altered tumor incidence and organ distribution of tumors induced by NDEA.
Asunto(s)
Grasas de la Dieta/efectos adversos , Dietilnitrosamina , Lípidos/sangre , Neoplasias Hepáticas Experimentales/inducido químicamente , Alanina Transaminasa/sangre , Animales , Aspartato Aminotransferasas/sangre , Biotransformación , Peso Corporal/efectos de los fármacos , Membrana Celular/metabolismo , Colesterol/sangre , Colesterol/metabolismo , Sistema Enzimático del Citocromo P-450/metabolismo , Ácidos Grasos/metabolismo , Glutatión/metabolismo , Incidencia , Hígado/efectos de los fármacos , Hígado/metabolismo , Hígado/ultraestructura , Masculino , Microsomas Hepáticos/metabolismo , Neoplasias Experimentales/inducido químicamente , Oxidación-Reducción , Fosfolípidos/metabolismo , Ratas , Ratas Endogámicas , Distribución Tisular , gamma-Glutamiltransferasa/sangreRESUMEN
Male rats were fed, from weaning onwards, either 2, 12.5 or 25% sunflower seed oil (polyunsaturated fatty acids, PSA) or lard (saturated fatty acids, SFA) and from the age of 15 weeks subgroups were given N-nitrosodimethylamine (NDMA) for 30 weeks. Blood levels of lipids were assayed and during the study exhaled ethane was measured as an index of in vivo lipid peroxidation (LPO). At the age of 50 weeks, rats were killed and livers were analysed for tumours. PSA diets decreased plasma cholesterol and triglyceride concentrations vs. respective SFA diet; NDMA administration did not affect plasma cholesterol but enhanced triglyceride concentration. NDMA markedly enhanced LPO. An increase in dietary fat content from 2 to 25% enhanced ethane exhalation, more in rats fed PSA than the SFA diet. In the 25% PSA group, indomethacin in the diet strongly inhibited LPO. Prevalence of liver haemangiosarcomas increased from 42% to 80% (p less than 0.05) in NDMA-treated animals when PSA increased from 2 to 25%; in the group having a 25% PSA diet containing indomethacin, the NDMA-induced tumour incidence was reduced to 64%. In NDMA-treated rats fed SFA diets the prevalence of haemangiosarcoma increased from 43% (2% fat) to 67% (25% fat). The data show that NDMA modifies plasma lipids and increases LPO. The quantity and saturation degree of fats altered the frequency of chemically-induced tumours and modified LPO. As an index of free radical reactions, LPO may have an important role in carcinogenesis. Dietary fat thus appears to promote carcinogenesis through mechanisms that involve LPO.
Asunto(s)
Transformación Celular Neoplásica/efectos de los fármacos , Grasas de la Dieta/efectos adversos , Neoplasias Hepáticas/inducido químicamente , Animales , Biomarcadores , Análisis Químico de la Sangre , Colesterol/sangre , Dimetilnitrosamina/farmacología , Glutatión/metabolismo , Indometacina/farmacología , Peroxidación de Lípido , Lípidos/sangre , Hígado/metabolismo , Masculino , Peptidil Transferasas/análisis , Ratas , Ratas Endogámicas , Triglicéridos/sangre , Aumento de PesoRESUMEN
The pesticide Deltamethrin, a synthetic pyrethroid, was studied for carcinogenicity in long-term experiments in mice and rats. Mice were given Deltamethrin by gavage in arachis oil at 0, 1, 4 or 8 mg/kg body wt for 2 years. A group of untreated controls was also available. Rats received 0, 3 or 6 mg/kg body wt. Deltamethrin in arachis oil for 2 years. In mice, an increased incidence of lymphomas was observed in the groups receiving 1 and 4 mg/kg body wt., but not in the group treated with 8 mg/kg body wt. Deltamethrin. In rats, an increased incidence of thyroid tumours was noted, but, no clear dose-response relationship was shown. Deltamethrin does not appear to be carcinogenic in mice or rats, but further studies are needed on the group of compounds to which this substance belongs.
Asunto(s)
Carcinógenos , Insecticidas/toxicidad , Piretrinas/toxicidad , Adenoma/inducido químicamente , Animales , Pruebas de Carcinogenicidad , Relación Dosis-Respuesta a Droga , Femenino , Neoplasias Hepáticas Experimentales/inducido químicamente , Neoplasias Pulmonares/inducido químicamente , Linfoma/inducido químicamente , Masculino , Ratones , Ratones Endogámicos C57BL , Nitrilos , Ratas , Neoplasias de la Tiroides/inducido químicamenteRESUMEN
Transplacental carcinogenesis represents a good model in which to study the involvement of tissue-specific oncogene activation in carcinogenesis because a single exposure to a carcinogen induces tumors at various sites. We tested tumors of the skin, liver, and lung produced in mice after transplacental 7,12-dimethylbenz[a]-anthracene (DMBA) exposure for possible activation of ras genes. XbaI restriction fragment-length polymorphism analysis has shown that exposure to DMBA in utero may result in appearance of A----T transversion at the second position of codon 61 of Ha-ras oncogene in skin and liver tumors but not in lung tumors. Moreover, DNA samples isolated from spontaneous and DMBA-induced lung and liver tumors were analyzed for mutations at the same position of Ki-ras oncogene using differential hybridization with specific oligonucleotides. Among five spontaneous lung tumors, three cases of A----G transition, and one case of A----T transversion were found, whereas four of ten lung tumors of DMBA-treated animals were positive for A----T mutation. No Ki-ras mutation was detected in one spontaneous and four DMBA-induced hepatomas. In two cases, we revealed Ki-ras A----T mutation in the lung tumor and Ha-ras mutation in the liver tumor taken from the same animal. These results indicate first that DMBA treatment may induce A----T mutation at the second position of codon 61 both in Ha-ras and in Ki-ras and, second, that the role of different activated oncogenes in carcinogenesis may differ, depending on the tissue in which the tumor develops.
Asunto(s)
Genes ras , Neoplasias Hepáticas Experimentales/genética , Neoplasias Pulmonares/genética , Mutación , Neoplasias Cutáneas/genética , 9,10-Dimetil-1,2-benzantraceno , Animales , Codón , Femenino , Enfermedades Fetales/inducido químicamente , Neoplasias Hepáticas Experimentales/inducido químicamente , Neoplasias Pulmonares/inducido químicamente , Ratones , Especificidad de Órganos , Polimorfismo de Longitud del Fragmento de Restricción , Embarazo , Neoplasias Cutáneas/inducido químicamenteRESUMEN
Fenvalerate is a widely used pesticide, which has been shown recently to be nonmutagenic. We studied its carcinogenicity in a long-term experiment in inbred C57Bl/6 mice given 0, 40 and 80 mg/kg body weight fenvalerate (99% pure) by gavage on 5 days/week for 104 weeks. Survival was decreased especially among females receiving the high dose. Exposure to fenvalerate resulted in a slight increase in the incidence of liver-cell tumours over that in controls only in male mice receiving the high dose. No significant difference in the incidence of other types of tumours was observed in treated groups when compared with controls. Fenvalerate-induced microgranulomas occurred concomitantly in the liver, spleen and lymph nodes of male and female mice, but their overall incidence did not increase with dose. In a separate experiment, groups of SJL/ola female mice were administered two different samples of fenvalerate (92% and 99% pure) once per week for 12 weeks. In animals that received 92% pure compound, the latent period for induction of lymphomas was shortened and their incidence increased, when compared with the group receiving 99% pure fenvalerate and with controls.
Asunto(s)
Insecticidas/toxicidad , Neoplasias Hepáticas Experimentales/inducido químicamente , Linfoma/inducido químicamente , Piretrinas/toxicidad , Animales , Cricetinae , Relación Dosis-Respuesta a Droga , Femenino , Granuloma/inducido químicamente , Masculino , Mesocricetus , Ratones , Ratones Endogámicos C57BL , NitrilosRESUMEN
In rats, hexachlorobenzene (HCB) causes uroporphyria and liver tumours predominantly in females. To investigate the promotional properties of HCB, male and female rats received diethylnitrosamine (DEN) in the drinking water (0.015%) for 3 weeks. After a 2-week recovery period rats were fed control diet or one containing HCB (0.02%) for 30 weeks. HCB was an efficient promoter of DEN-initiated hepatocarcinogenesis in both sexes as judged by the size and numbers of visible tumours and by the percentage of liver sections that stained strongly positive for gamma-glutamyltranspeptidase (GGT) activity. Tumours were larger in males whereas regions of GGT-positive tumour and non-tumour tissue were greater in females. Inhibition of the haem biosynthesis enzyme uroporphyrinogen decarboxylase (UD) only occurred in the liver of females treated with HCB or DEN/HCB. In the latter group, UD was inhibited both in and outside tumours whereas uroporphyrin only accumulated in non-cancerous tissue. No significant inhibition of UD was observed in the liver of males. In another study, rats received one i.p. dose of DEN (20 mg/kg) and after 3 weeks were fed HCB for 30 weeks. Numbers of GGT-positive foci were greatly increased by HCB in both sexes, but especially in males (1.4-fold greater than females). Thus HCB was shown to be a promoter of hepatocarcinogenesis. However, the lack of a consistent marked sex difference suggests that this is only a partial explanation for the induction of tumours which mainly occur in females when this chemical is administered alone for prolonged periods.
Asunto(s)
Carcinógenos , Clorobencenos/toxicidad , Dietilnitrosamina/toxicidad , Hexaclorobenceno/toxicidad , Neoplasias Hepáticas Experimentales/patología , Hígado/patología , Porfirias/inducido químicamente , Animales , Peso Corporal/efectos de los fármacos , Femenino , Hígado/efectos de los fármacos , Masculino , Tamaño de los Órganos/efectos de los fármacos , Ratas , Ratas Endogámicas F344 , Valores de Referencia , Factores SexualesRESUMEN
Pre-loading of C57BL/10ScSn mice with iron greatly sensitizes them to the induction of hepatic porphyria caused by hexachlorobenzene (HCB) (Smith and Francis, 1983). HCB will also cause liver tumours in experimental animals. Elevated liver iron stores are implicated in the development of some human liver cancers. To determine whether iron overload will potentiate the hepatocarcinogenicity of HCB, male C57BL/10ScSn mice received a single dose of iron-dextran complex or the dextran carrier and were then fed HCB in the diet (0.01%) for up to 18 months. A very clear potentiation by iron of liver tumour incidence occurred. Of the mice which received HCB, but no iron, for 12 months a low incidence of liver hyperplastic nodules was observed, whereas preadministration of iron increased the incidence. After 18 months, all surviving mice initially given iron followed by HCB developed advanced hepatic nodules and 90% had hepatocellular carcinomas. No tumours were seen in animals that only received HCB. Nodules were not seen in iron-dosed mice receiving control diet, but another novel observation was that these animals developed porphyria by 6 months. Although iron enhanced tumour formation in the presence of HCB, the foci, nodules and carcinomas formed all excluded iron. Preliminary studies with the DBA/2 strain suggested that these mice were considerably less susceptible to potentiation by iron.
Asunto(s)
Clorobencenos/toxicidad , Hexaclorobenceno/toxicidad , Hierro/toxicidad , Neoplasias Hepáticas Experimentales/inducido químicamente , Animales , Sinergismo Farmacológico , Hipertrofia/inducido químicamente , Hierro/metabolismo , Hígado/metabolismo , Hígado/patología , Neoplasias Hepáticas Experimentales/metabolismo , Neoplasias Hepáticas Experimentales/patología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos DBA , Necrosis , Porfirias/inducido químicamenteRESUMEN
The transplacental initiation-postnatal promotion model of mouse skin carcinogenesis is useful in studying the molecular and cellular mechanisms of perinatal carcinogenesis. Offspring transplacentally exposed to an initiating dose of a carcinogen typically do not produce any skin tumours in the absence of postnatal treatment; many skin tumours appear only when they are treated with tumour-promoting agents postnatally. Tumour-promoting agents alone produce no skin tumours or only a few. Thus, two stages of carcinogenesis, initiation and promotion, can be conveniently separated. Our results indicate that fetal c-Ha-ras can be transplacentally activated through a specific point mutation by a carcinogen. However, since postnatal promotion was essential for the production of tumours, they also suggest that a cell harbouring such a mutation may remain dormant until it encounters a tumour-promoting stimulus. Since a higher fraction of carcinomas than papillomas contained the specific mutation in Ha-ras, it is postulated that those papillomas with the point mutation have a selective advantage to progress towards carcinomas.
Asunto(s)
Cocarcinogénesis , Efectos Tardíos de la Exposición Prenatal , Proto-Oncogenes/efectos de los fármacos , Neoplasias Cutáneas/genética , Animales , Animales Recién Nacidos , Carcinógenos/farmacología , Femenino , Regulación Neoplásica de la Expresión Génica , Genes ras/efectos de los fármacos , Ratones , Embarazo , Neoplasias Cutáneas/inducido químicamenteRESUMEN
Partial hepatectomy (PH) is known to enhance liver carcinogenesis when it is performed several hours before or after administration of a hepatocarcinogen. This effect has been attributed to cell proliferation, which is induced by PH and is a necessary step for fixation of DNA damage leading to initiated cancer cells. We now report for the first time that PH can also increase the tumour incidence, and decrease the latency period, when it is performed 8-10 weeks before treating rats with the hepatocarcinogen N-nitrosodiethylamine. This animal model may offer a tool for investigating the underlying mechanism of the 'memory effect' and increased tumour susceptibility of liver cells after PH. Additionally, it could be explored as a more sensitive rodent bioassay for testing putative carcinogens.
Asunto(s)
Cocarcinogénesis , Hepatectomía , Neoplasias Hepáticas Experimentales/etiología , Animales , Dietilnitrosamina , Neoplasias Hepáticas Experimentales/inducido químicamente , Masculino , Ratas , Ratas Endogámicas , Factores de TiempoRESUMEN
Sister chromatid exchange (SCE) frequencies in peripheral lymphocytes are a frequently used endpoint to indicate exposures to genotoxins in groups of humans. The aim of this study was to ascertain, in an experimental design, whether or not SCE rates have any association with the risk of cancer at the individual level in rats exposed to a known carcinogen. Individual SCE rates were determined in three consecutive analyses in cultured blood lymphocytes of 50 adult male Wistar rats. Analyses were done before as well as 24 hr and 7 days after a single intraperitoneal administration of 0, 25, 50, or 75 mg/kg of N-ethyl-N-nitrosourea (ENU). The animals were followed until death; also, the relationship between SCEs and carcinogenic outcome, i.e., the presence or absence of tumors, and their latency period were examined. ENU significantly decreased the life expectancy of the rats. The tumor types most clearly associated with ENU treatment were various gliomas and thyroid-gland and testicular tumors. ENU induced a moderate (maximally 1.6-fold) increase in the mean frequency of SCEs/cell at both sampling times after treatment. The effect was somewhat more pronounced 1 day rather than 1 week after treatment. The mean SCE rates in rats with ENU-specific cancers or in animals with early or multiple tumors did not differ from those in animals that survived no less than 65 weeks or longer without developing tumors. In ENU-treated animals with tumors, no relationship was found between the mean SCE rate and survival time. It is concluded that in outbred Wistar rats the SCE response in cultured lymphocytes does not indicate individual susceptibility to the carcinogenic action of ENU. On a group basis, however, animals with high SCE rates were shown to have increased risk of cancer.
Asunto(s)
Etilnitrosourea/farmacología , Intercambio de Cromátides Hermanas/efectos de los fármacos , Animales , Pruebas de Carcinogenicidad/métodos , División Celular/efectos de los fármacos , Ensayos de Selección de Medicamentos Antitumorales/normas , Linfocitos/ultraestructura , Índice Mitótico/efectos de los fármacos , Ratas , Ratas EndogámicasRESUMEN
Mouse skin tumors were produced after transplacental initiation [with 7,12-dimethylbenz(a)anthracene], only when the skin was treated post-natally with a tumor-promoting agent (12-O-tetradecanoyl phorbol 13-acetate). DNA analysis of tumors showed that all carcinomas analyzed contained a specific mutation (A to T transversion) at the 61st codon of c-Ha-ras. Fifty per cent of the papillomas analyzed also had this same mutation. The A to T transversion at the 61st codon of Ha-ras was heterozygous in all positive papillomas and carcinomas. No such mutation was found when benzo(a)pyrene was used as an initiating agent. These results indicate that fetal c-Ha-ras can be transplacentally activated through a specific point mutation by a carcinogen, but a cell harboring such a mutation may remain dormant until it encounters a tumor-promoting stimulus.