W. Kloas
Humbodt University, Endocrinology, Faculty Member
SIGLEAvailable from TIB Hannover: RN 8908(2000,494) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Umwelt, Naturschutz und Reaktorsicherheit, Bonn (Germany)DEGerman
African clawed toad (Xenopus laevis) has been established as a very suitable model for studying the effects of Endocrine Disrupting Chemicals (EDCs) on reproductive biology. In a previous study we demonstrated severe alterations of testis... more
African clawed toad (Xenopus laevis) has been established as a very suitable model for studying the effects of Endocrine Disrupting Chemicals (EDCs) on reproductive biology. In a previous study we demonstrated severe alterations of testis organization (i.e. reduction of tubule diameter and number of germ cell nests and occurrence of small oocytes) in adult male X. laevis following a four weeks exposure to water from the river Lambro (LAM), a contaminated watercourse from Northern Italy. Data were compared with controls and exposed to ethinylestradiol (EE2), tamoxifen (TAM), methyl-dihydrotestosterone (MDHT) and flutamide (FLU), 10-8 M, as positive controls for (anti)estrogenic and (anti)androgenic activities. In this study, following the same experimental design, our attention was focused on the effects on the spermatogenic process. Germ cell nest profile was analysed in both paraffin and resin embedded testis within ten tubule sections for each specimen, numbered and classified int...
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Vaccine adjuvants are classified according to their properties of either inducing the persistence of antigens within the animal after immunisation and/or activation of the animal's immune response. The adjuvant effect of low intensity... more
Vaccine adjuvants are classified according to their properties of either inducing the persistence of antigens within the animal after immunisation and/or activation of the animal's immune response. The adjuvant effect of low intensity low frequency sonophoresis (LFS) was tested in rainbow trout using an Aeromonas salmonicida bacterin vaccine administered by immersion vaccination using LFS at 37 kHz. The adjuvant effect obtained with LFS was compared with that of normal immersion or intraperitoneal injection vaccination. Quantitative PCR was used to measure bacterial DNA in vaccinated fish up to 35 days post-vaccination, while RT-qPCR was used to assess gene expression during the early and late immune response post-vaccination. Results showed that antigen uptake in the gills was significantly higher in the group exposed to low intensity LFS compared to the other two vaccination groups 15 min post-vaccination, but this initially high uptake did not persist over the rest of the exp...
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Research Interests: Endocrinology, Physiology, Zoology, Biology, Medicine, and 15 moreXenopus, Internal Medicine, Aldosterone, Animals, Corticosterone, In Vivo, Xenopus laevis, Catecholamine, Veterinary Sciences, Catecholamines, Secretion, Atrial Natriuretic Factor, Adrenal glands, Adrenal cortex hormones, and In Vitro Techniques
Aromatase P450 (P450 arom; Cyp19) is a key enzyme for vertebrate reproduction and brain development that catalyzes the conversion of androgens to estrogens. The aim of this study was to improve the knowledge on EDC effects by analysing... more
Aromatase P450 (P450 arom; Cyp19) is a key enzyme for vertebrate reproduction and brain development that catalyzes the conversion of androgens to estrogens. The aim of this study was to improve the knowledge on EDC effects by analysing their potential impact on brain P450 arom in adult Xenopus laevis exposed for 4 weeks to an environmental sample, the water of the river Lambro (LAM), the most polluted tributary of the Po river in North Italy. Other groups were exposed to individual compounds 10(-8) M tamoxifen (TAM), ethinylestradiol (EE2), flutamide (FLU) and methyldihydrotestosterone (MDHT) known for their (anti)estrogenic and (anti)androgenic modes of action. Expression of CYP19 was evaluated in brain extracts by quantitative RT-PCR, using a pair of primers located in the open reading frame (ORF) that allowed the simultaneous amplification of all transcripts (Aro-ORF) and a pair of primers specific for brain aromatase (Aro-B). Significant increase in Aro-ORF and Aro-B mRNA levels were observed in both females and males exposed to LAM. Different changes were observed for the model compounds using two pairs of primers. Aro-ORF mRNA expression was significantly increased in EE2 and MDHT exposed males and in FLU-exposed females, while it was significantly decreased in TAM exposed females. Aro-B mRNA was significantly increased in both sexes exposed to FLU and decreased in TAM exposed females. In conclusion, aromatase mRNA in the brain of X. laevis was regulated differentially in a gender specific manner by certain (anti)estrogenic and (anti)androgenic EDCs, supporting previous hypotheses that diverse compounds present in the river Lambro may induce feminization and demasculinization effects.
Research Interests: Endocrinology, Physiology, Biology, Rivers, Medicine, and 15 moreBrain development, Italy, Brain, Internal Medicine, General, Endocrine disruptors, Animals, Enzyme, mRna expression levels, Mode of action, Endocrine Disruptors, Open Reading Frame, aromatase, reverse transcriptase polymerase chain reaction, and mRNA expression
Recent in vitro studies suggest that insulin-like growth factor I (IGF-I) is involved in cell differentiation and steroidogenesis in the gonad and could therefore function as an important trigger in vivo. In this study, sensitive... more
Recent in vitro studies suggest that insulin-like growth factor I (IGF-I) is involved in cell differentiation and steroidogenesis in the gonad and could therefore function as an important trigger in vivo. In this study, sensitive real-time RT-PCR assays were used to determine IGF-I and the IGF-I receptor (IGF-IR) mRNA expression in maturing male and female sterlet (Acipenser ruthenus) over a period of two years: In the first year, females entering vitellogenesis (maturing female group, MFG) revealed an increase of IGF-I expression in the ovaries in contrast to females that did not enter vitellogenesis (non-maturing female group, NMFG). Congruently, IGF-IR expression was elevated in females at the onset of vitellogenesis (MFG), decreased towards the first winter, and increased to similar levels at late vitellogenesis in the second winter just prior to spawning. In the second year, NMFG reached the onset of vitellogenesis. Here, IGF-I and IGF-IR reached similar levels as previously observed in the first year in MFG. In males, low and constant IGF-I expression was observed in the testis, whereas IGF-IR was expressed at a constant high level comparable to those of females entering vitellogenesis. These findings suggest an involvement of IGF-I as an important paracrine regulator of gonad maturation, particularly in the ovary.
Research Interests: Endocrinology, Biology, Medicine, Cell Differentiation, Internal Medicine, and 15 moreFemale, Animals, Male, Fishes, First Year, In Vitro Studies, Base Sequence, Oocytes, Gonads, Biochemistry and cell biology, Insulin Like Growth Factor, Gene Expression Regulation, Molecular Sequence Data, Gonad, and mRNA expression
One century ago, Acipenser sturio was a prevalent species of the fish communities in all major German rivers. Since then, the population sizes decreased rapidly due to overfishing, pollution and hydroconstruction. Under a scientific... more
One century ago, Acipenser sturio was a prevalent species of the fish communities in all major German rivers. Since then, the population sizes decreased rapidly due to overfishing, pollution and hydroconstruction. Under a scientific cooperation agreement with the French ...
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ABSTRACT After temperature-induced puberty at 12 °C for 12 weeks, the progression of gametogenesis in maturing pikeperch (Sander lucioperca) was studied at 12 °C, 14 °C, 16 °C, and 18 °C, compared with a control group reared at 23 °C. The... more
ABSTRACT After temperature-induced puberty at 12 °C for 12 weeks, the progression of gametogenesis in maturing pikeperch (Sander lucioperca) was studied at 12 °C, 14 °C, 16 °C, and 18 °C, compared with a control group reared at 23 °C. The plasma concentration of the sex steroids estradiol (E2), testosterone (T), 11-ketotestosterone (11-KT), and 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P) as well as the histology of the gonad confirmed the successful induction of puberty in all treatment groups and an advanced gonadal maturation until the end of the experiment in both. After 16 weeks at 14 °C, 80% of the female pikeperch examined were in mid vitellogenesis compared with a slower progression at 12 °C, 16 °C, and 18 °C. After 20 weeks, all fish reared at 14 °C accom-plished mid vitellogenesis accompanied by a significant up-regulation of E2, which was also detected in the con-specifics reared at 12 °C and 16 °C, although not as advanced. In females reared at 18 °C, only a small percentage reached mid vitellogenesis accompanied by decreasing E2 concentrations, succeeding the induction of puberty at week 12. After 20 weeks, the level of T as well as 11-KT peaked in fish of both sexes kept between 12 °C and 16 °C. As in females, temperature influenced postpubertal maturation in males, which was indicated by significant tem-perature dependent changes of the sex steroids. E2 plasma concentrations in males exhibited a bimodal pattern with two maxima, first after 12 weeks at the onset of puberty and the second after week 26, coinciding with the end of spermatogenesis as indicated by milt production. In conclusion, postpubertal temperatures around 14 °C promoted a complete ripening in pikeperch of both sexes within 8 weeks, whereas higher temperatures constrained full gonadal maturation. Furthermore, with reference to the optimal temperature for the induction of puberty previously discussed, slightly higher temperatures around 14 °C are optimal for postpubertal matura-tion. This clearly indicates the existence of a dynamic temperature influence for optimal maturation due to postpubertal inhibition of maturation at temperatures higher than 18 °C. Consequently, in addition to the role of low temperatures in the induction of puberty, this is the first evidence that emphasizes the need for a closely controlled temperature range to be maintained during the ongoing maturation, which should be considered in year round production of pikeperch. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.
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: This study is part of a project aimed at developing and validating novel noninvasive methods for the detection of biomarkers of endocrine disrupters (EDs) directly in the mucus of aquatic species, to identify novel functional... more
: This study is part of a project aimed at developing and validating novel noninvasive methods for the detection of biomarkers of endocrine disrupters (EDs) directly in the mucus of aquatic species, to identify novel functional biomarker(s) for EDs, and to verify their applicability for field studies. The multidisciplinary approach chosen aims at the development of an integrated testing strategy utilizing in vitro protocols to identify water and sediment fractions with potential endocrine‐disrupting activity; the identification, characterization, and measurement of new biomarker(s) for EDs; the development and validation of a dipstick‐based test method; and the development of (computer‐assisted) predictive models. Some results of the first year of the project are presented here.
Research Interests: Computer Science, Medicine, Multidisciplinary, Humans, Mice, and 15 moreEndocrine disruptors, Female, Animals, Prediction Model, Field Study, Biomarker, First Year, Biological markers, Endocrine Disruptors, Toxicity Tests, Carps, Multidisciplinary Approach, Predictive value of tests, Test Methods, and Integration Testing
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Owing to an increasing world population and a rising demand in protein for food and feed, alternative protein sources are needed. In addition, existing food and protein supplies such as wild and farmed fish need to be secured. Insects and... more
Owing to an increasing world population and a rising demand in protein for food and feed, alternative protein sources are needed. In addition, existing food and protein supplies such as wild and farmed fish need to be secured. Insects and more specifically the black soldier fly (BSF; Hermetia illucens) larvae, are discussed as an alternative animal protein source and a potential fish meal (FM) replacer in aquaculture. They can be sustainably reared on biogenic residues. In a literature study, the technical potential of occurring biogenic residues in Germany for the production of BSF larvae is estimated and their suitability as a FM replacement in aquafeed for the production of rainbow trout is evaluated. According to literature, up to 50% of FM can be substituted by BSF larvae meal in the feed of rainbow trout. For the annual German rainbow trout production of 8,466 t, 2,699 t BSF larvae meal (40.7% protein d.m.) is required to replace 1,556 t FM (70.9% protein d.m.). The demand for...
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ABSTRACT Deoxynivalenol (DON) is one of the most frequently detected mycotoxins in agricultural commodities used as animal feedstuff in Central Europe. This study focuses on determining effects of diets containing DON on oxidative stress... more
ABSTRACT Deoxynivalenol (DON) is one of the most frequently detected mycotoxins in agricultural commodities used as animal feedstuff in Central Europe. This study focuses on determining effects of diets containing DON on oxidative stress markers and detoxifying enzymes in rainbow trout (Oncorhynchus mykiss). The fish were fed with commercial pellets containing DON at a concentration of 2 mg kg−1. Selected enzymes were measured in liver, gill and caudal kidney of the fish after 23 and 32 days of the experiment. Significant differences between the control and experimental groups were observed concerning activities of glutathione peroxidase (GPx) in kidney, glutathione reductase (GR) in gill and kidney, catalase (CAT) in kidney and liver and glutathione S-transferase (GST) in gill and liver. No significant differences were found for superoxide dismutase (SOD) gene expression, lipid peroxidation (TBARS) and the ferric reducing ability of plasma (FRAP). The data show that DON in the diet at the concentration below EC recommendation (2006/576/EC) induces oxidative stress in the rainbow trout.
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Summary Amphibians are the classical models for hormone induced sex reversaland thus the basic mechanisms underlying sexual differentiationare of pivotal significance for understanding the modes of action ofendocrine disrupting compounds... more
Summary Amphibians are the classical models for hormone induced sex reversaland thus the basic mechanisms underlying sexual differentiationare of pivotal significance for understanding the modes of action ofendocrine disrupting compounds (EDC) in amphibians. The occurenceof sexual steroids, androgens and estrogen, as well as their correspondingreceptors were measured during complete development of Xenopuslaevis . Sexual steroids are derived from maternal origin and endogenousproduction seemed to occur only at very late metamorphic stages.Androgen (AR)- and estrogen receptor (ER)-mRNA were regulated upvery early during the sensitive stages for sex reversal. Additional invivo experiments for sexual differentiation using (anti)estrogenic and(anti)androgenic EDC resulted in a recent hypothesis for sexual differentiationin amphibians.
Beta2-adrenergic receptors were detected in bovine oviductal epithelium by use of receptor binding studies and expression analysis. Complementary DNA cloning gave use to the first full-length bovine beta2-adrenoceptor messenger RNA... more
Beta2-adrenergic receptors were detected in bovine oviductal epithelium by use of receptor binding studies and expression analysis. Complementary DNA cloning gave use to the first full-length bovine beta2-adrenoceptor messenger RNA sequence (2030 bases). Receptor bioactivity in oviduct epithelial cells was characterized by specific ligand interaction and consequent cAMP generation. Expression studies demonstrated an estrous cycle-dependent regulation, with higher transcript levels and significantly increased binding capacity during the luteal phase. After progesterone supplementation, oviduct epithelial cells showed elevated receptor expression in culture, supporting the hypothesis that progesterone up-regulates the beta2-adrenergic receptor within these cells. It seems likely that catecholamines from the circulation or from innervation might be able to influence reproductive success by regulating oviductal secretion.
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The biological role of atrial natriuretic peptide (ANP) for the adrenal tissue of the teleost fish Cyprinus carpio, the carp, was investigated using in vitro autoradiography to study ANP binding sites, immunohistochemistry to localize... more
The biological role of atrial natriuretic peptide (ANP) for the adrenal tissue of the teleost fish Cyprinus carpio, the carp, was investigated using in vitro autoradiography to study ANP binding sites, immunohistochemistry to localize ANP-like peptides, and in vitro perifusion to measure adrenal cortisol and catecholamine release. 125I-labeled rat ANP-(99-126) [125I-rANP-(99-126)] binding was present in adrenal tissue exhibiting positive cooperativity with a half-maximal binding concentration (EC50) of 87 +/- 15 pM and a maximal binding capacity (Bmax) of 56 +/- 11 amol/mm2 (n = 3). 125I-rANP-(99-126) binding was competitively displaced by unlabeled ANP analogues with an intact disulfide bridge showing a lower affinity than the iodinated ligand. By the use of immunohistochemistry, ANP immunoreactivity was found in the majority of the phenylethanolamine N-methyl-transferase-immunoreactive, i.e., epinephrine-synthesizing cells. In vitro, ANP elevated both basal and acetylcholine-stimu...
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1. In the atlantic hagfish (Myxine glutinosa) binding sites for atrial natriuretic peptide (ANP) were visualized by autoradiography in contractile structures of the renal system (glomeruli, neck segment, and archinephric duct) and in the... more
1. In the atlantic hagfish (Myxine glutinosa) binding sites for atrial natriuretic peptide (ANP) were visualized by autoradiography in contractile structures of the renal system (glomeruli, neck segment, and archinephric duct) and in the aorta. 2. Since the location of binding sites is comparable to that in higher vertebrates including man, these results suggest that ANP may act as a hormone already in cylcostomata.
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Research Interests: Animal Husbandry, Growth, Female, Animals, Male, and 15 moreGrowth and development, Endocrine, Laboratory experiment, Herbicides, Ovarian Follicle, Environmental Conditions, Larva, Larvae, Ovary, Larval Development, Atrazine, Environmental Protection Agency, Estradiol, positive control, and Pharmacology and pharmaceutical sciences
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This review provides a critical analysis of the biological effects of the most widely used plasticizers, including dibutyl phthalate, diethylhexyl phthalate, dimethyl phthalate, butyl benzyl phthalate and bisphenol A (BPA), on wildlife,... more
This review provides a critical analysis of the biological effects of the most widely used plasticizers, including dibutyl phthalate, diethylhexyl phthalate, dimethyl phthalate, butyl benzyl phthalate and bisphenol A (BPA), on wildlife, with a focus on annelids (both aquatic and terrestrial), molluscs, crustaceans, insects, fish and amphibians. Moreover, the paper provides novel data on the biological effects of some of these plasticizers in invertebrates, fish and amphibians. Phthalates and BPA have been shown to affect reproduction in all studied animal groups, to impair development in crustaceans and amphibians and to induce genetic aberrations. Molluscs, crustaceans and amphibians appear to be especially sensitive to these compounds, and biological effects are observed at environmentally relevant exposures in the low ng l −1 to µg l −1 range. In contrast, most effects in fish (except for disturbance in spermatogenesis) occur at higher concentrations. Most plasticizers appear to ...
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The ciliate Ichthyophthirius multifiliis is among the most pathogenic parasites of fish maintained in captivity. In the present study, the effects of the crude methanolic extract of leaves of Mucuna pruriens and the petroleum-ether... more
The ciliate Ichthyophthirius multifiliis is among the most pathogenic parasites of fish maintained in captivity. In the present study, the effects of the crude methanolic extract of leaves of Mucuna pruriens and the petroleum-ether extract of seeds of Carica papaya against I. multifiliis were investigated under in vivo and in vitro conditions. Goldfish (Carassius auratus auratus) infected with the parasites were immersed for 72 h in baths with M. pruriens extract, and for 96 h in baths with C. papaya extract. There was a 90% reduction in numbers of I. multifiliis on fish after treatment in baths of each plant extract at 200 mg l(-1 )compared to untreated controls. Consequently, parasite-induced fish mortality was reduced significantly. A complete interruption of trophont recruitment was achieved by immersion in the M. pruriens extract. In vitro tests led to a 100% mortality of I. multifiliis in 150 mg/l M. pruriens extract, and in 200 mg/l of C. papaya extract after 6 h. Although the active constituents of the medicinal plant extracts are still unknown, we have demonstrated that they have potential for effective control of I. multifiliis.
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The purpose of this study was to determine under laboratory conditions over a period of 311 days if infection with the nematode Anguillicola crassus induces stress in European eels (Anguilla anguilla), and stimulates the endocrine stress... more
The purpose of this study was to determine under laboratory conditions over a period of 311 days if infection with the nematode Anguillicola crassus induces stress in European eels (Anguilla anguilla), and stimulates the endocrine stress axis as measured by serum cortisol levels. Eels were experimentally infected with 3rd-stage larvae (L3) in different doses to simulate natural conditions with varying infection pressures. Blood samples were drawn from the caudal vein every 2 weeks and serum cortisol concentrations were determined by radioimmunoassay (RIA). The results showed that the application of L3 resulted in a significant increase in the cortisol levels. The period of time at which elevated cortisol values were observed was consistent with the time of larval development and the appearance of adult A. crassus. Thus, there is a stress response to the larval and young adult stages, but no chronic response to older adults. Therefore, it is likely that infection of eels under natura...
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To investigate whether the stress response of European eels infected with Anguillicola crassus is influenced by environmental pollutants, experimentally infected eels were exposed to Cd and/or to 3,3', 4,4',... more
To investigate whether the stress response of European eels infected with Anguillicola crassus is influenced by environmental pollutants, experimentally infected eels were exposed to Cd and/or to 3,3', 4,4', 5-pentachlorobiphenyl (PCB 126). Serum cortisol and glucose concentrations of these eels were monitored over a period of 103 days and were compared with data from infected, unexposed eels as well as with data from uninfected eels. Additionally, the levels of cortisol were correlated with concentrations of Anguillicola-specific antibodies. All eels showed an initial increase of the cortisol levels until day 63. This general elevation of plasma cortisol is most likely due to handling stress, as all eels were repeatedly netted and afterwards inoculated with a feeding tube. At the end of the exposure period eels which were infected and those which were infected and simultaneously exposed to Cd and PCB showed significantly higher levels than the controls. The general course of serum glucose levels in eels resembled that of cortisol. Accordingly, Spearman correlation analysis revealed that an increase in serum cortisol concentrations is correlated with rising levels of glucose. With respect to immune-endocrine interactions a significant negative correlation between cortisol and anti-A. crassus antibodies was found. Our data show that A. crassus is the most potent stressor for European eels among the treatments tested within this study. This is important in terms of ecotoxicological studies as the main effects are caused by parasites rather than chemicals. Accordingly, effects of parasites on the physiological homeostasis of organisms must be considered in ecotoxicology. From the parasitological point of view our results suggest that probably as part of an unbalanced host-parasite interaction A. crassus evokes a strong cortisol response in A. anguilla, thereby suppressing the immune response which in turn enables the parasite to establish. The parasite-induced stress response in the newly adopted European eel might be one of the factors which contributes to the extremely effective colonizing strategy of A. crassus.
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Research Interests: DNA replication, Gene expression, Biological Sciences, real time PCR, Brain, and 15 moreMolecular and cellular biology, Thyroid gland, Endocrine disruptors, Animals, Vertebrates, Protein Metabolism, Endocrine Disruptors, Goiter, Thyroid Stimulating Hormone, Gene expression profiling, Thyroid Function, Differential expression, Thyroid hormone, Medical and Health Sciences, and Growth Regulator
Research Interests: Immunohistochemistry, Comparative Study, Reproductive Biology, In Situ Hybridization, Biological Sciences, and 11 moreLiver, Female, Animals, Tilapia, Oreochromis mossambicus, Ovary, Growth Factor, In Situ Hybridisation, Insulin Like Growth Factor, Molecular Sequence Data, and Medical and Health Sciences
Abstract The functional status of organ systems involved into the processing of exogenous food is critical for the survival and growth of fish early life stages. The present study on laboratory-reared larval turbot, ScophthaImus maximus,... more
Abstract The functional status of organ systems involved into the processing of exogenous food is critical for the survival and growth of fish early life stages. The present study on laboratory-reared larval turbot, ScophthaImus maximus, provides an overview on the ...
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Insulin-like growth factor I (IGF-I) and its receptor are present in human and rat anterior pituitary. However, few data exist on the potential presence of IGF-I or its receptor in the non-mammalian pituitary and the cellular sites of... more
Insulin-like growth factor I (IGF-I) and its receptor are present in human and rat anterior pituitary. However, few data exist on the potential presence of IGF-I or its receptor in the non-mammalian pituitary and the cellular sites of IGF-I production have not been identified in any species. Thus, we investigated the anterior pituitary of the clawed frog Xenopus laevis which is widely used to study growth and differentiation. The study was performed with antisera against mammalian insulin-like growth factor I (IGF-I), prolactin (PRL) and growth hormone (GH) using immunohistochemical and immunocytochemical techniques. IGF-I binding was determined by in-vitro receptor autoradiography. The PRL-and GH-immunoreactive cells exhibited distinct distribution patterns. Neither at the light nor the electron microscopical level any colocalization of PRL-and GH-immunoreactivities was apparent. The PRL-immunoreactive cells exhibited round granules of medium electron density (mean diameter: 312 nm) and the GH-immunoreactive cells spherical granules of medium electron density (mean diameter: 165 nm). By the use of serial semithin sections IGF-I-immunoreactivity was exclusively located in PRL-immunoreactive cells. At the ultrastructural level, IGF-I-immunoreactivity was confined to the secretory granules in coexistence with PRL-immunoreactivity using the double labelling immunogold technique. Specific IGF-I binding sites were localized throughout the pituitary. The results provide evidence for a concomitant release of PRL and IGF-I and suggest autocrine/paracrine actions of IGF-I in the anterior pituitary.
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Sexual steroids have major regulatory functions in gonadal development, maturation of gametes and sexual differentiation in vertebrates. Previous studies in amphibians provided evidence that dihydrotestosterone and activity of 5-α... more
Sexual steroids have major regulatory functions in gonadal development, maturation of gametes and sexual differentiation in vertebrates. Previous studies in amphibians provided evidence that dihydrotestosterone and activity of 5-α reductases might play a significant role in androgen-mediated reproductive biology. To test the involvement of 5-α reductases in maturation of gametes in amphibians, Xenopus laevis was exposed to finasteride (FIN), a known inhibitor of 5-α reductase enzyme activity. In a long-term exposure from stage 46 to 66, severe disruption of spermatogenesis was observed in histological analysis of testes as detected by occurrence of empty spermatocysts, while ovaries remained unaffected. Real-time PCR analyses of male and female brain revealed an increase of LHβ mRNA and a decrease of FSHβ mRNA in males, suggesting a signalling on testes that could result in increased steroidogenesis and reduced Sertoli cell proliferation. Accordingly, the mRNA expression of P450 sid...
Research Interests: Enzyme Inhibitors, Molecular endocrinology, Brain, Spermatogenesis, Female, and 12 moreAnimals, Male, tESTIS, Clinical Sciences, Larva, Xenopus laevis, Veterinary Sciences, Finasteride, Ovary, Follicle stimulating hormone, reverse transcriptase polymerase chain reaction, and Paediatrics and reproductive medicine
In this study, carp Cyprinus carpio were injected with various steroid compounds, including synthetic and natural progestogens and the glucocorticoid cortisol, to investigate effects on leucocytes isolated from their kidneys. Injection of... more
In this study, carp Cyprinus carpio were injected with various steroid compounds, including synthetic and natural progestogens and the glucocorticoid cortisol, to investigate effects on leucocytes isolated from their kidneys. Injection of cortisol led to an increased spleeno-somatic index (I(S)) on day 21 post-injection (pi) and immunosuppressive effects measured as decreased nitric oxide (NO) production and increased arginase activity in isolated leucocytes on days 14 and 21 pi, respectively. Moreover, reduced NO production was also observed after injection of the synthetic progestogens, levonorgestrel (LEV) and medroxyprogesterone acetate. In addition, LEV influenced arginase activity in head kidney cells on day 14 and day 21 pi. This study is the first demonstration in fishes that the application of these steroid compounds in vivo affects NO production and arginase activity of isolated leucocytes.
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Embryos of Danio rerio are highly susceptible to extracts of the plants Tephrosia vogelii and Asystasia vogeliana. The concentration of the dried extracts at which 50% of the embryos were affected (EC 50) after 24 h exposure were 320 and... more
Embryos of Danio rerio are highly susceptible to extracts of the plants Tephrosia vogelii and Asystasia vogeliana. The concentration of the dried extracts at which 50% of the embryos were affected (EC 50) after 24 h exposure were 320 and 572 μg l− 1, respectively; ...
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In spite of the importance of IGF-I for growth and development, knowledge about regulation of its production in submammalian species is rather limited. In order to create a tool for investigation of direct regulatory effects on the... more
In spite of the importance of IGF-I for growth and development, knowledge about regulation of its production in submammalian species is rather limited. In order to create a tool for investigation of direct regulatory effects on the expression of IGF-I in bony fish liver, a primary cell culture of hepatocytes from Oreochromis mossambicus, the tilapia, was established. The cells were viable for up to 3 days and IGF-I mRNA synthesis was detected by northern blot and semiquantitative reverse transcriptase (RT)-PCR. Northern blot analysis of the primary cultured hepatocytes revealed four different IGF-I transcripts, 0.5, 1.9, 3.9 and 6.0 kb in size, which were identical to those in liver tissue. However, the expression rate was weaker than that in liver. The direct effects of recombinant tilapia (rt) growth hormone (GH) and salmon (s) IGF-I on the expression of IGF-I in primary cultured hepatocytes were investigated in time-course and dose-response experiments. In untreated cultures, IGF...
Research Interests: Endocrinology, Animal Production, Cell Culture, Growth Hormone, Animals, and 12 moreGrowth and development, Behavioral Animal Models, Clinical Sciences, mRna expression levels, Tilapia, Hepatocytes, Veterinary Sciences, Oreochromis mossambicus, Primary Culture, Reverse Transcriptase, Time Course, and reverse transcriptase polymerase chain reaction
Environmental compounds can interfere with endocrine systems of wildlife and humans. These so-called endocrine disrupters (ED) are known to affect reproductive biology and thyroid system. The classical model species for these endocrine... more
Environmental compounds can interfere with endocrine systems of wildlife and humans. These so-called endocrine disrupters (ED) are known to affect reproductive biology and thyroid system. The classical model species for these endocrine systems are amphibians and therefore they can serve as sentinels for detection of the modes of action (MOAs) of ED. Recently, amphibians are being reviewed as suitable models to assess (anti)estrogenic and (anti)androgenic MOAs influencing reproductive biology as well as (anti)thyroidal MOAs interfering with the thyroid system. The development of targeted bioassays in combination with adequate chemical analyses is the prerequisite for a concise risk assessment of ED.
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Transition from previtellogeneic to vitellogenic oocyte growth is a critical phase for folliculogenesis in sturgeon and may often be postponed for several years. Recent findings on the involvement of insulin-like growth factor I (IGF-I)... more
Transition from previtellogeneic to vitellogenic oocyte growth is a critical phase for folliculogenesis in sturgeon and may often be postponed for several years. Recent findings on the involvement of insulin-like growth factor I (IGF-I) in cell differentiation processes of oocyte follicle and ovarian steroidogenesis of teleosts in vitro led to the hypothesis that paracrine IGF-I could function as a potential trigger in vivo. For the first time, IGF-I and its corresponding receptor (IGF-IR) were identified in a non-teleostean fish. Real-time PCR assays for IGF-I and IGF-IR mRNA were established, normalising mRNA expression of the target genes to beta-microglobulin (beta2m). We clearly show that expression of IGF-I in the gonad is a substantial source for IGF-I-mediated effects in follicles compared to liver, brain, muscle and adipose tissue. Among these tissues, IGF-IR mRNA was highest in the gonad. With regard to different cohorts of coexisting follicles, highest expression of IGF-I and IGF-IR were met in developing follicles, indicating that IGF-I functions as an intraovarian modulator of follicle faith. Comparing previtellogenic follicles in females that matured within two years with non-maturing females f the same age, revealed an increases of 2.3-fold for IGF-I and 2.8-fold for IGF-IR mRNA expression in maturing females. These findings implicate an important role of paracrine IGF-I in early vitellogenesis and identify it as candidate vitellogenesis inducing factor (VIF), determining the faith of the follicle.