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Biomedical subjects

G Zbinden

Publications and source records attributed to G Zbinden.

At least 55 records · Page 3Linked to original sources
PubMed1985

Thrombogenic effects of xenobiotics.

The mechanisms by which xenobiotics may cause or promote thrombosis include vascular damage, induction of a hypercoagulable state and disturbances of blood flow. This paper discusses the methods available to detect various types of thrombogenic substances. Pathomorphological techniques are best suited to demonstrate thrombosis caused by localized vascular damage or generalized endothelial lesions. For the assessment of disseminated microcirculatory thrombosis, the consumption of platelets and clotting factors and the appearance of specific platelet proteins and fibrinogen and fibrin split products can be determined in the blood. Hypercoagulability which is defined as a perturbation of the hemostatic equilibrium resulting in a shift in the direction of thrombosis, is of particular importance in toxicology. Many in vitro, ex vivo and in vivo methods have been proposed to detect and to measure the ability of xenobiotics to induce a prethrombotic state. Their usefulness is demonstrated with several examples.

Adrenocorticotropic Hormone↗
PubMed1985

Early biochemical and morphological changes of the rat adrenal medulla induced by xylitol.

Long-term administration of high doses of xylitol and other polyols in rats has been associated with an increase in adrenal medullary hyperplasia and neoplasia. In order to exclude age-related factors and to differentiate between unspecific stress reactions and direct effects of the compound administered, a model was developed for quantifying early adrenomedullary responses. Male SD rats were fed xylitol (10% or 20% in the diet) for 2 and 8 weeks, and early biochemical changes were correlated with a stereological analysis of the adrenal medulla. At first, the in vivo rate of catecholamine (CA) biosynthesis was slightly decreased (at 2 weeks). This was followed by an increase in dopamine-beta-hydroxylase (DBH) activity (at 8 weeks). By that time, the total chromaffin cell volume had increased and the number of chromaffin cells per reference volume had decreased in a dose-dependent way. The total number of chromaffin cells per adrenal gland showed a distinct tendency towards an increase. Adrenal epinephrine and norepinephrine contents were not altered, and both tyrosine hydroxylase and phenylethanolamine-N-methyltransferase activities remained unchanged. These data suggest that continued xylitol administration evoked an inhibitory effect on CA synthesis that, together with stimulation of the adrenal medulla brought about by the compound, resulted in compensatory medullary hypertrophy and hyperplasia.

Adrenal Medulla↗
PubMed1985

Ethical considerations in toxicology.

Since most of the research necessary for the safety evaluation of chemicals requires the killing of laboratory animals, toxicologists are faced with an ethical conflict between their professional duties and the interests of the animals. In the past, the protection of consumers against chemical injury was considered to be of the greatest importance, and society approved of all efforts to detect even the slightest hazards from man-made and environmental chemicals. In recent years, toxicologists have become aware of their ethical responsibilities not only for the safety of the human population but also for the welfare of the animals. They have begun to review the classical toxicological procedures critically and now require that the maximum amount of relevant information is obtained from the smallest number of laboratory animals. Toxicologists have also become aware of the alternative methods that permit the investigation of toxicological responses in unicellular organisms and cell cultures. The problem of testing chemicals for irritant properties on skin and mucous membranes is an excellent example of how concern for animals has generated a range of original and imaginative research leading not only to a reduction in the use of animals but also to a more efficient and scientific approach to an important health problem.

Animals↗
PubMed1985

Interpretation of cell toxicity data for the estimation of potential irritation.

Three cytotoxicity assays were evaluated using 57 chemicals of various classes (inorganic and organic metal salts, solvents, detergents, reagents, drugs) which have widely different mechanisms of cytotoxicity. Baby hamster kidney fibroblasts (BHK-21/C13) and early (Keller) and late (MRC-5) passage human fibroblasts were used to measure cell detachment, cloning efficiency, and growth inhibition under subconfluent culture conditions. For the majority of chemicals, for which comparisons were made, the ranking order was roughly the same in all three tests and with all three cell types. However, for some chemicals specific growth effects could either be detected or excluded because the relationship between the data from the detachment assay and that from one of the growth assays was characteristically altered. The ranking order resulting from our in vitro data correlated better with threshold limit values for human workroom air (TLV/TWA) than with LD50 values (rat, oral). Correlations with data from Draize skin and eye irritation tests were not determined since the available in vivo values were derived using various different scoring systems. However, when our in vitro data were used to divide the chemicals into three crude classes, (i) non-irritant, (ii) mild to moderate irritant, or (iii) strong irritant or corrosive, and the results were compared with the known irritation potential for skin and mucous membranes derived from human exposure data, the in vitro data were more than 80% predictive of the in vivo classifications.

Animals↗
PubMed1985

Aristolochic acid induces 6-thioguanine-resistant mutants in an extrahepatic tissue in rats after oral application.

The mutagenic activity of the natural plant product aristolochic acid (AA) was tested in the Granuloma Pouch Assay, which detects gene mutations induced in a subcutaneous granuloma tissue of rats. After direct exposure of the target tissue, AA induced high frequencies of mutants at a relatively low cytostatic/cytotoxic level. AA was more potent that N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) at equimolar doses. After oral application of AA, a dose-dependent mutagenic activity was seen. In contrast a very weak and inconsistent mutagenic effect was seen after systemic application of MNNG. These observations suggest that after oral application AA is not detoxified efficiently and can exert its mutagenic activity in extrahepatic tissues whereas MNNG is detoxified to a large extent at the site of administration.

Administration, Oral↗
PubMed1980

Assessment of emetine cardiotoxicity in a subacute toxicity experiment in rats.

We explored the usefulness of cardiovascular function studies for the detection and characterization of emetine cardiotoxicity in a subacute toxicity experiment. Rats received 1 mg/kg, s.c., emetine five times weekly for up to 7 weeks. In unanesthetized animals, statistically significant changes of the electrocardiogram (EKG) appeared in the following sequence: prolongation of QRS interval (5th day), flattening of T wave (beginning of 4th week), and prolongation of PR interval (end of 4th week). Terminal cardiovascular studies were conducted under urethane anesthesia. EKG changes were comparable to those recorded in conscious rats, but no decrease in T wave voltage occurred. Blood pressure and heart rate remained unchanged. Cardiac output was decreased after 5 and 7 weeks of treatment, when heart weights were also significantly reduced. The response of cardiac output and mean arterial blood pressure to intravenously injected norepinephrine and epinephrine remained unchanged. Catecholamine-induced arrhythmias occurred less frequently in emetine-treated animals than in controls. No significant structural lesions of the heart muscle were detected by light microscopy. The cardiotoxic effects observed in rats were similar to those reported in humans receiving the usual therapeutic dose of approximately 1 mg/kg/day. We conclude that cardiovascular function studies can make an important contribution to the predictive value of animal toxicity experiments.

Anesthesia↗
PubMed1980

Electrocardiographic changes in rats during chronic treatment with antidepressant and neuroleptic drugs.

Five antidepressants, 3 phenothiazines and 5 butyrophenone neuroleptics were administered to rats orally at maximally tolerated doses for 22 weeks. The electrocardiogram (ECG) was recorded weekly. In animals treated with antidepressants quinidine-like changes of the atrioventricular and intraventricular conduction developed. There were also elevation of T-wave and right rotation of the electrical axis. Dibenzepine had the least effect on the ECG. In the group of phenothiazines chlorpromazine induced tachycardia and thioridazine widening of the QRS complex. Prothipendyl had no effect. ECG-changes induced by some of the butyrophenone derivatives were tachycardia and widening of the QRS-complex. In rats treated with protriptyline the ECG changes were correlated with drug concentrations in serum and myocardial tissue. The studies provided a quantitative assessment of the cardiac effects of clinically proven psychotropic drugs. They will be useful as a baseline for the preclinical evaluation of new derivatives.

Animals↗
PubMed1980

Biological assessment of chemical DNA damage in germ cells of male rabbits.

DNA damage represents a key step in mutagenesis and carcinogenesis. Excision repair has been described to be the major pathway restoring damaged DNA. Assaying DNA repair may thus illuminate the mechanism of mutagenesis and carcinogenesis and serve as an indicator of the mutagenic and carcinogenic potential of environmental chemicals and drugs. The paper demonstrates a practical application of these concepts. DNA damage induced by chemical substances in male germ cells of rabbits was assessed by the demonstration of DNA repair synthesis in meiotic and post-meiotic maturation stages. Incorporation of tritium-labeled thymidine was monitored in spermatozoa obtained by serial ejaculation. The test was validated with several standard mutagens and carcinogens, and its usefulness was demonstrated with a study on 3 suspected genotoxic drugs, i.e. hycanthone, isoniazid, and metronidazole.

Animals↗
PubMed1979

Unscheduled DNA synthesis in male rabbit germ cells induced by methylmethane sulfonate, cyclophosphamide and adriamycin.

Male rabbit germ cells were labelled by intratesticular injection of [3H]-thymidine (3H-T). In sperms of control animals, radioactivity was first demonstrated between the 40th and 43rd day after labelling, corresponding to preleptotene spermatocytes. In rabbits treated with 22.5 mg/kg methylmethane sulfonate (MMS), significant radioactivity was shown in sperms collected from day 19 ownwards. These cells derived from spermatocyes and early spermatids at the time of labelling. 3H-T incorporation into these cell populations represents unscheduled DNA synthesis (UDS), a repair process initiated after chemical damage of germ cell DNA. After i.v. injection of 20 mg/kg cyclophosphamide, an alkylating agent that must be activated, labelled sperms were found 28--37 days after treatment. This shows that UDS took place in spermatocytes during the pachytene and zygotene stages. Adriamycin (1.0 and 3.0 mg/kg) induced UDS during pachytene and zygotene stages of spermatogenesis. Sperm counts decreased during spermatogonial stages by a factor of about ten in cyclophosphamide and adriamycin treated rabbits. It was not changed after MMS-treatment.

Animals↗
PubMed1979

Application of fine-needle aspiration biopsy for the diagnosis of dysplastic and neoplastic liver cell changes induced by N-nitrosomorpholine in rats.

Male rats were treated with the hepatocarcinogen, N-nitrosomorpholine (NNM, 10 mg ad 100 ml drinking water) for 19 weeks. Repeated fine-needle aspiration biopsies of the liver were performed percutaneously. Cytomorphologic and cytochemical criteria were used for the characterization of dysplastic and carcinoma cells. The alterations seen in the smears were correlated with histopathologic findings in the punctured liver lobes. Cells showing type I dysplasia were recognized in smears obtained from day 7 on. They corresponded to the swollen, glycogen-free cells developing in zone 3 of the Rappaport acinus during the early treatment phases. In later stages type I dysplastic cells were observed in smears. This coincided with the development of neoplastic nodules seen in histopathologic preparations. Carcinoma cells were recognized first after 15 weeks. Marked gamma-glutamyl transpeptidase (gamma-GT) activity could be demonstrated cytochemically in biopsy smears and biochemically in biopsy homogenates during the early phases of NNM-treatment. Simultaneously, a rise in gamma-GT activity was also observed in the serum.

Animals↗
PubMed1979

The no-effect level, an old bone of contention in toxicology.

This discussion of the NEL presents some thoughts how toxicologists could be encouraged to use more sophisticated modern techniques for the study of various environmental chemicals. It is proposed to use the concept of the NEL only for data obtained by conventional techniques in routine toxicity experiments. Information on the mechanisms of the biologic effects of chemicals should, whenever possible, be used preferentially for the assessment of human risk and should therefore also be considered for the establishment of the ADI.

Dose-Response Relationship, Drug↗
PubMed1979

Differential DNA damage induced by chemical mutagens in cells growing in a modified Selye's granuloma pouch.

Rapid growth of granulation tissue was induced in rats by injection of croton oil into a subcutaneous air pocket. Growth characteristics of the granulation tissue were evaluated by histopathologic techniques and measurement of 3H-thymidine incorporation into DNA. The DNA of cells growing in the granuloma was labeled with 3H-thymidine. Subsequently, 4 classes of test chemicals (monofunctional and polyfunctional alkylating agents, DNA intercalating agents and chemicals not known to interact with DNA) were injected intraperitoneally. The presence of single-strand breaks was assayed in DNA of granuloma tissue using the alkaline elution technique. DNA breaks were primarily induced by monofunctional alkylating agents and were characteristic for each compound. DNA from animals treated with polyfunctional alkylating agents and DNA-intercalating agents showed a variable degree of resistance to methylmethane sulfonate-induced DNA breakage.

Alkylating Agents↗
PubMed1979

Quantitative analysis of rat behavior patterns in a residential maze.

A method for monitoring spontaneous locomotor patterns of rats during one day is described. The animals' locomotion is registered in a residential maze by 18 optical gates connected to a computer. Status changes of each optical gate are stored on a disk file and can be retrieved for complete session reconstruction and data analysis. The general features of a rat's behavior in the maze are discussed. Quantitative analyses and statistical comparisons between two sessions spaced two weeks apart and between a group of 4 control animals and 4 rats treated in utero with methylmercury chloride are performed. Following parameters are analysed as functions of time and maze location: locomotor and local activity, occupational duration and time per visit in the maze compartments. Angular dependences of path decisions and regional preferences of crossing at the alley bifurcations are observed. No changes of the measured parameters can be observed between the first and second sessions. Methylmercury treatment results in a consistently lower local activity during the night period and in differences of path preferences.

Animals↗