The carcinogenic effect of inhaled asbestos fibers

Changes in responses of low-frequency and high-frequency LGB neurons were studied on anesthetized and paralyzed rabbits after strichninization of the visual cortex. It was found that in the group of low-frequency neurons the average discharge frequency of responses increased and latencies decreased indicating a dominance of corticofugal facilitation. On the contrary, in the group of high-frequency neurons the average discharge frequency of responses decreased and latencies increased. This suggests a dominance of corticofugal inhibition. The existence of reciprocal corticofugal influences on the neurons of different components of the visual pathways is assumed.     

Assessment of the carcinogenic potential of polyglycerol polyricinoleate (PGPR) in rats and mice

The carcinogenic potential of the food emulsifier ADMUL WOL brand of polyglycerol polyricinoleate (PGPR) was evaluated in rats and mice. Groups of 60 male and 60 female rats were given purified diets containing 5% of either PGPR or groundnut oil for 2 years. Groups of 25 male and 25 female mice were given purified diets containing 5% of either PGPR or groundnut oil for 80 weeks. No carcinogenic effect of PGPR was observed. In addition, dietary PGPR had no adverse effect on growth, food consumption, longevity and haematology. Organ weight analysis revealed an increase in liver and kidney weight in both male and female rats and female mice. Histological analysis of tissues revealed no treatment related adverse effects.     

Exposure to ceramic fibers in the work environment. II. Occupational exposure to dust in plants producing ceramic fiber; fibrogenic effect of the fibers

The aim of the work was to assess the exposure to dust containing ceramic fibres among workers employed in the plant producing aluminosilicate fibres, and to investigate fibrogenic properties of produced ceramic aluminosilicate fibres (L-1). The studies carried out in the work environment revealed that workers were exposed to dust containing respirable fibres from materials produced (fibres, mats). Mean concentrations of these fibres ranged from 0.07 to 0.37 f/cm3 and they were considerably lower than MAC value (1 f/cm3) proposed for respirable ceramic fibres. Mean total dust concentrations ranged from 0.4 to 2.9 mg/m3, and at two working posts they exceeded the proposed MAC value (2 mg/m3). In animal experiments (Wistar female rats) a single dose (25 mg) of L-1 fibres administered intratracheally induced pathological symptoms in lungs, limited to reactive changes in the form of granuloma with weakly pronounced cytolysis, and mean levels of hydroxyproline in the lungs did not differ significantly from the physiological level. The L-1 fibre was classified in the group of dusts with insignificant fibrogenic effects.     

Microtensile superplasticity in ceramic fibers

Superplastic experiments were carried out in tension on small specimens having a cross section of approx. 50 × 1.1 μm, and a gage length of 4 mm. The specimens, in the form of fibers, were prepared by lithography from thin films that were obtained by physical vapor deposition. Experiments with ZrO₂-2.6 mol% Y₂O₃ exhibited a threshold stress for superplastic flow. While the measurements of the average flow stress were in agreement with data from bulk materials, the stress-strain curves obtained from the microspecimens were serrated, which we attribute to discrete grain sliding events. The serrations are belived to occur because the gage section contained relatively few grains. A new approach for conceptualizing superplastic flow in ultrafine grained ceramics is proposed.     

Dynamic fatigue experiments on optical fibers

Optical fibers should have a minimum life of 25 years. Proof testing is usually done in order to have only high-strength fibers and to evaluate their lifetimes. The behavior of the fibers is studied in terms of the mechanism of slow growth of microcracks. A maximum stress that will be allowed in the subsequent usage of the fiber is then calculated, performing extrapolations from measurements which last a few months to times which last more than 25 years. As might be expected, papers have been published that indicate this procedure leads to inaccurate predictions. Work reported here involves fibers with a broad distribution of strengths. These were used for the purpose of reducing test times. Dynamic fatigue tests were done under atmospheric and inert environments. Results were used to obtain portions of the universal fatigue curve in order to assess the potential accuracy of long-term extrapolation from high-strength fiber tests.     

The effect of steroid contraceptives on the concentrations of brain monoamines in rats and mice

The effect of three estrogen-progestin combinations on biogenic amines in discrete brain areas of rats and mice has been investigated. With the exception of a significant decrease of brain 5-hydroxyindolacetic acid in the rats treated for 30 days with the combination norethynodrel + mestranol, no significant changes in the levels of serotonin, noradrenaline or dopamine in the rat brain were found following the administration of the compounds under study. On the other hand, in mice moderate but significant changes in the levels of serotonin, dopamine, noradrenaline and 5-hydroxyindolacetic acid were found in various brain areas depending on the estrogen-progestin combination used. The potential importance of these effects for the contraceptive as well as for some central actions of these compounds is discussed.     

Urinary excretion of dioxidine and quinoxidine in experiments on mice]

The extent of hybrid formation between the ribosomal ribonucleic acid (r-RNA) of Hyphomicrobium strain B-522 and deoxyribonucleic acid (DNA) from bacteria of 21 different genera was examined. Three generalized groupings were formed. Group I (72-100%) consisted entirely of other strains of Hyphomicrobium. Representatives of the genera Rhodopseudomonas, Chromatium, Caulobacter, Prosthecomicrobium, Rhodomicrobium, Hyphomonas, and Hyphomicrobium made up group II (49-69%). The remaining Gram-negative, Gram-positive, and cell wall--less bacteria fell into group III (12-40%). The taxonomic implications of these results are discussed.     

Anti-hyperalgesic effect of an ethanolic extract of propolis in mice and rats

Abdominal obesity, anxiety, and depression have been found to cluster in several studies. To further characterize these associations, the following study was performed. In a population of 51-year-old men (N = 284), measurements of obesity (body mass index [BMI]) and body fat distribution (waist to hip ratio [WHR] and sagittal trunk recumbent diameter [D]) were analyzed in relation to dexamethasone (0.5 mg) inhibition of cortisol secretion, measured as salivary cortisol. Symptoms of anxiety and depression were defined by a validated questionnaire. Furthermore, testosterone, insulin-like growth factor-I (IGF-I), insulin, glucose, and serum lipid levels were measured. Twenty-five men (8.8%) had symptoms of anxiety and depression. BMI, WHR, and D correlated negatively with testosterone, except for BMI in the anxio-depressive (ADP) group. IGF-I showed no significant relationship. Furthermore, fasting insulin and the insulin to glucose ratio correlated positively and high-density lipoprotein (HDL) cholesterol correlated negatively with BMI, WHR, and D in the total study population and in the subgroups. Total and low-density lipoprotein (LDL) cholesterol showed no significant relationships. Correlation coefficients tended to be higher in ADP men. Dexamethasone inhibition showed a negative significant relationship with BMI (rho = -.47, P = .025), WHR (borderline, rho = -.37, P = .086), and D (rho = -.43, P = .046) only in the ADP group. Comparing the ADP group versus the group without anxio-depression (ADO) and high or low BMI (P = .008), WHR (P = .026), and D (P = .012) showed blunted dexamethasone inhibition only in ADP men with high anthropometric measurements. These findings suggest there is a subgroup with elevated BMI, WHR, and D in whom a blunted dexamethasone response is found associated with traits of anxiety and depression, conditions characterized by such an abnormality. The reason for the association might be insufficient control of cortisol secretion, followed by visceral fat accumulation.     

Identification of ''genotoxic'' and ''non-genotoxic'' alerts for cancer in mice: the carcinogenic potency database

Chemokines are a superfamily of pro-inflammatory polypeptide cytokines that selectively attract and activate different cell types. Many patho-physiological conditions require the participation of chemokines, including inflammation, infection, tissue injury, allergy, cardiovascular diseases, as well as malignant tumors. Chemokines activate cells through their binding to shared or unique cell surface receptors which belong to the seven-transmembrane, G-protein-coupled Rhodopsin superfamily. The role of chemokines in malignant tumors is complex: while some chemokines may enhance innate or specific host immunity against tumor implantation, others may favor tumor growth and metastasis by promoting tumor cell proliferation, migration or neovascularization in tumor tissue. In this review, the authors summarize some of the recent advances in chemokine research and emphasis is made on the effect of chemokines in tumor growth and metastasis.     

Time dependent crack growth in ceramic matrix composites with creeping fibers

Crack growth in ceramic matrix composites with creeping fibers has been investigated using a time dependent bridging law to describe the effect of fibers bridging a matrix crack. The fibers were assumed to creep linearly and the matrix was assumed to be elastic. Time dependent crack growth was predicted assuming that matrix crack growth occurs when the stress intensity factor at the matrix crack tip reaches a constant critical value. Crack growth rates are presented as a function of crack length and time. Domains of stable and unstable crack growth are outlined. The solutions illustrate that stable crack growth consists of a relatively brief period of decerelation followed by acceleration to large crack lengths, with crack velocity approaching constancy only at loads very near the matrix cracking stress and for very long cracks. Finally, the time needed to grow a long matrix crack is compared with a rough estimate for the time needed to rupture fibers. A transition is expected from life dominated by matrix crack growth at low stress to life dominated by fiber creep rupture after crack growth at higher stresses.     

The effect of recombinant human thyrotropin (rhTSH) on thyroid function in mice and rats

Lymphocytic gastritis is a recently described gastric inflammation, characterized by an increased intraepithelial lymphocytic infiltrate mainly composed of T-lymphocytes. Endoscopically it correlates mainly with diffuse varioliform gastritis. Ménétrier's disease is a hypertrophic gastropathy with enlarged gastric folds. The histological picture is that of foveolar hyperplasia and glandular cysts of the mucosa. A few small series of lymphocytic gastritis with microscopic and endoscopic features of Ménétrier's disease have been published previously. We describe a similar case associated with a gastric adenocarcinoma.     

The carcinogenic response in mice to the topical application of propane sultone to the skin

The carcinogenic effects of limited and repeated skin applications of propane sultone were investigated in three strains of mice, CF1, C3H and CBah (a hairless strain). Propane sultone was shown to be carcinogenic when given as a single application of a 25% w/v solution in toluene and also following twice weekly application of a 2.5% w/v solution for up to 58 weeks. More limited exposure to 2.5% w/v solutions of propane sultone resulted in a few skin tumours, although the incidences were not statistically significant. Most neoplasms were papillomas or carcinomas, although a small number of mesenchymal tumours of dermal origin also developed. No skin neoplasms were found in any control mice. The skin application of propane sultone was associated with a statistically significant increase in the incidence of systematic neoplasia in CFl and C3H mice. The exposed CFl mice had a higher incidence of neoplasms of lymphoreticular and lung origin, while female C3H mice showed a higher incidence of mammary gland and uterine tumours. In mice exposed to beta-propiolactone as a positive control, neoplasms developed at the site of application but, there was no evidence of increased systemic neoplasis in contrast to the findings with ptopane sultone.     

The multipotential carcinogenic action of N-ethyl-N-nitrosourea administered neonatally to mice

Newborn A, C57BL, DBAf and IF mice were injected s.c. with a range of doses of N-ethyl-N-nitrosourea (ENU). A high proportion of treated mice developed tumours, particularly hepatomata, pulmonary adenomata and carcinomata, and malignant lymphomata of thymus and spleen. Liver tumours occurred most frequently in C57BL and DBAf mice, lung tumours in A mice, and lymphomata in A and DBAf mice. A small proportion of C57BL, DBAf and IF mice developed tumours of the nervous system. The results are discussed with reference to the ready induction of nervous system tumours in similarly treated rats, and their relevance for human cancer.     

The effect of ethanol upon early development in mice and rats. XXIV. The effect of acute ethanol intoxication upon implantation in mice

The primary mode of human immunodeficiency virus (HIV) transmission worldwide is by exposure to the virus at vaginal, rectal, and oral mucosal surfaces. To understand HIV/simian immunodeficiency virus (SIV) transmission events at mucosal portals of entry, we used the SIV-macaque model to determine if mucosal surfaces function as barriers and select for particular viral genotypes. Rhesus macaques were inoculated intravaginally, intracolonically, intrarectally, or orally with the complex primary viral isolate SIV/DeltaB670. Peripheral blood mononuclear cells, collected within the first two weeks postinoculation, were cloned and sequenced from all infected macaques. In the majority of the animals analyzed, multiple genotypes were identified, independent of the route of infection. These findings suggest that the mucosal barrier may play a minor role in the genotypic selection observed during sexual transmission of HIV and emphasize the need to evaluate the viral diversity present within the mucosal secretions of chronically infected individuals.     

Reduced serotonergic immunoreactive fibers in the forebrain of alcohol-preferring rats

Our previous study indicated that 5-hydroxytryptamine (5-HT) immunoreactive fiber densities were decreased in specific areas of the brain in alcohol-preferring rats (P) when compared with alcohol-nonpreferring rats (NP). The results of our current study show that there are quantitative and qualitative differences in 5-HT innervation in other selected regions of the forebrains of P rats. The 5-HT fiber density in the brains of young adult P and NP rats was measured by immunocytochemistry and quantitative image analysis. A routine error of two-dimensional quantitation of nerve fiber was addressed and an adjustment was made. The amount of 5-HT fibers was significantly lower in CA4 and fasciola cinereum of the dorsal hippocampus, caudate-putamen, and hypothalamus of the P as compared with NP rats (unpaired Student's t tests). In examining the fiber types, we found that, in the frontal cortical and hippocampal regions, where normally fine 5-HT fibers with small varicosities and thick 5-HT fibers with large varicosities coexist, fewer fine 5-HT fibers were seen in P rats as compared with NP rats. The fine fibers are known to be vulnerable to abusive drugs. These observations indicate that (a) there are quantitative differences in 5-HT innervation or that the 5-HT in some 5-HT fibers is reduced to a level undetectable by immunocytochemistry, and (b) the fine 5-HT fibers are specifically reduced to a greater degree in the selected brain regions of P rats when compared with that of NP rats. The involvement of the 5-HT system in the alcohol abuse is discussed.     

A multiyear workplace-monitoring program for refractory ceramic fibers: findings and conclusions

Results of a monitoring program carried out by members of the Refractory Ceramic Fibers Coalition as part of a Consent Agreement with the U.S. Environmental Protection Agency to measure workplace concentrations of refractory ceramic fiber (RCF) are presented. More than 700 personal monitoring samples were collected and analyzed annually from workers in RCF production and processing plants, as well as from those employed by customers/end users. The data indicate that (i) approximately 90% of time-weighted average (TWA) workplace concentrations are below the industry's recommended exposure guideline of 1 fiber per cubic centimeter TWA; (ii) workplace concentrations vary with functional job category; (iii) concentrations are approximately lognormally distributed; (iv) workplace concentrations are generally decreasing; (v) there are significant differences in workplace concentrations among plants operated by both RCF producers and customers; (vi) equations can be developed to interconvert data analyzed using different measurement techniques and counting rules; (vii) usage of respirators varies with the functional job category of the worker and the average fiber concentration; and (viii) workplace samples differ from those used in animal inhalation experiments in terms of the ratio of respirable particles to fibers.     

The effect of autografting on the myosin composition in skeletal muscle fibers

The purpose of the study was to investigate the changes in myosin heavy chain (MHC) and myosin light chain (MLC) isoforms following autotransplantation of extensor digitorum longus muscles. Muscles were grafted in "standard" and "nerve-intact" conditions. MHC and MLC isoforms were analyzed by sodium dodecyl sulphate gel electrophoresis. Changes in MHC isoforms 10, 30, and 60 days after grafting were similar in the "standard" and the "nerve-intact" grafts. In contrast to MHC, changes in MLC were different in the 10th day groups, but the same in the 30th day groups. Sixty days after grafting the content of MLC isoforms was the same as the control muscles. These data indicate that transient loss of functional innervation, even for a short time, has permanent effect on the composition of MHC but not MLC isoforms in regenerating skeletal muscle fibers.