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  • 1
    Electronic Resource
    Electronic Resource
    Different signal transduction by epidermal growth factor may be responsible for the difference in modulation of amino acid transport between fetal and adult hepatocytes (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 155 (1993), S. 549-555 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: [1-14C]-2-aminoisobutyric acid (AIB) uptake and signal transduction pattern after epidermal growth factor (EGF) stimulation were examined in freshly isolated hepatocytes from 20-day-old fetuses and 3-month-old rats. EGF induced a transient increase of AIB transport after 10 min only in adult animals; the observed unresponsiveness of fetal liver is not dependent on a lack of EGF receptors which are present though to a lesser extent on the plasma membrane in this period. As far as the production of the second messengers, inositol trisphosphate (IP3) and calcium, is concerned, substantial differences were found: EGF increased IP3 production in adult hepatocytes, whereas it had no effect in fetal ones. Moreover, the addition of EGF induced a calcium transient in hepatocytes from adult animals, while there was no increase in fetal cells. The lack of EGF effect on amino acid transport in fetal cells could be due to its inability to produce both IP3 and calcium transients, suggesting that this transduction pathway is not activated during fetal life.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041550313
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  • 2
    Electronic Resource
    Electronic Resource
    Biologic effects of prolonged exposure to ELF electromagnetic fields in rats. I. 50 Hz electric fields (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 14 (1993), S. 479-493 
    Details
    ISSN: 0197-8462
    Keywords: ELF ; electric fields ; growth curve ; hormones ; testes weight ; histology ; serum chemistry ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: A three-year investigation was conducted on the biological effects of high-intensity electric field exposures of rats for up to 18% of their life span. Two hundred and forty adult male rats, divided into groups of 20 animals each, were exposed at ground potential for 8 h/ day at 25-kV/m and 100-kV/m 50-Hz electric fields or were sham exposed for 280, 440, and 1240 h. The corresponding ages at sacrifice were 140, 164, and 315 days. An additional group of 40 rats was investigated under similar experimental conditions after 440 h of exposure at floating potential.Independent of exposure duration, mode of grounding, and field strength, no statistical differences in body weight, morphology, and histology of the liver, heart, mesenteric lymph nodes, and blood variables (hematology and serum chemistry) were found in comparison with sham-exposed animals. Plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (TS)at sacrifice varied widely among experimental animals in the same group but did not differ in exposed compared with sham-exposed rats. A nonsignificant tendency toward a decrease in the testes/body weight ratio was found after 1240 h of exposure. Microscopic examination of a large number of specimens showed no quantitative or qualitative statistical differences in testes alterations either among exposed animals or between exposed and their corresponding sham-exposed groups. We conclude that 50-Hz electric field exposure, even of long duration at very high field strengths, does not induce harmful effects on tissues with high cellular turnover rates and does not impair the reproductive function of rats. Moreover, after exposure, all variables investigated were well within the normal physiological range. © 1993 Wiley-Liss. Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bem.2250140508
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  • 3
    Electronic Resource
    Electronic Resource
    Studies on the possible biological effects of 50 Hz electric and/or magnetic fields: Evaluation of some glycolytic enzymes, glycolytic flux, energy and oxido-reductive potentials in human erythrocytes exposed in vitro to power frequency fields (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 14 (1993), S. 383-391 
    Details
    ISSN: 0197-8462
    Keywords: erythrocytes ; metabolism ; electric and/or magnetic fields ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: An attempt has been made to understand whether 50 Hz electric and magnetic fields (EMFs) are involved in producing bioeffects by exposing human erythrocytes in vitro. The study evaluated some key glycolytic enzymes, glucose consumption, lactate production, energy charge, 2,3-diphosphoglycerate, and reduced glutathione levels. all of which are biochemical parameters significant to erythrocyte function. Cells exposed to individual or superimposed EMFs have not shown any significant difference compared with the controls. © 1993 Wiley-Liss. Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bem.2250140410
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  • 4
    Electronic Resource
    Electronic Resource
    Biologic effects of prolonged exposure to ELF electromagnetic fields in rats: II. 50 Hz magnetic fields (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 16 (1995), S. 343-355 
    Details
    ISSN: 0197-8462
    Keywords: ELF magnetic field ; growth curve ; histology ; hematology ; serum chemistry ; neurotransmitters ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: To provide possible laboratory support to health risk evaluation associated with long-term, low-intensity magnetic field exposure, 256 male albino rats and an equal number of control animals (initial age 12 weeks) were exposed 22 h/day to a 50 Hz magnetic flux density of 5 μmT for 32 weeks (a total of about 5000 h). Hematology was studied from blood samples before exposure to the field and at 12 week intervals. Morphology and histology of liver, heart, mesenteric lymph nodes, and testes as well as brain neurotransmitters were assessed at the end of the exposure period. In two identical sets of experiments, no significant differences in the investigated variables were found between exposed and sham-exposed animals. It is concluded that continuous exposure to a 50 Hz magnetic field of 5 μT from week 12 to week 44, which makes up ˜70% of the life span of the rat before sacrifice, does not cause changes in growth rate, in the morphology and histology of liver, heart, mesenteric lymph nodes, testes, and bone marrow, in hematology and hematochemistry, or in the neurotransmitters dopamine and serotonin. © 1995 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bem.2250160602
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  • 5
    Electronic Resource
    Electronic Resource
    The hamster cheek pouch carcinogenesis model (1993)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 53 (1993), S. 83-90 
    Details
    ISSN: 0730-2312
    Keywords: intermediate biomarkers ; chemoprevention ; biological ; molecular ; genetic changes ; hamster ; buccal pouch ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The Syrian golden hamster cheek pouch carcinogenesis model is probably the best-known animal system that closely compares to events involved in the development of premalignant and malignant human oral cancers. Furthermore, it is one of the most well-characterized models for squamous cell carcinomas (SCCs). However, stages of carcinogenesis (initiation, promotion, and progression) have not been well-defined in this system. Basic understanding of the mechanism(s) of carcinogenesis in this organ is instrumental for the development of new strategies for chemoprevention and early chemointervention. To understand the important early events that occur in the hamster cheek pouch carcinogenesis model, we compared it to the mouse skin model, where a number of critical events have been well characterized. We determined that approximately 60% of the hamster cheek pouch SCCs have a mutation in codon 61 of the Ha-ras gene. We also established a two-stage carcinogenesis protocol in this model using a single dose of dimethylbenz(a)anthracene (DMBA) and multiple doses of benzoyl peroxide for 45 weeks. Twenty-five percent of tumors developed with this protocol had the same mutation in codon 61 of the Ha-ras gene, confirming that this mutation, as in the mouse skin model, is initiation-related. We examined the sequential expression of hyperplasia, micronucleated cells, ornithine decarboxylase (ODC) activity, polyamine levels, transglutaminase I activity, epidermal growth factor receptor (EGF-R) levels, keratins, γ-glutamyltranspeptidase (GGT), transforming growth factor -β1 (TGF-β1), leukoplakia, and carcinomas induced during carcinogenesis. A number of these important biological molecular and genetic markers could be excellent intermediate endpoints in assessing the effects of various chemopreventive agents to be tested in the hamster cheek pouch model and in human clinical trials.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240531012
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  • 6
    Electronic Resource
    Electronic Resource
    Cholesterogenesis and related enzymes in isolated rat hepatocytes during pre- and postnatal life (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 118 (1984), S. 62-66 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cholesterogenesis pathway during pre- and postnatal development was studied in isolated rat hepatocytes. No modified activity of cytosol acetoacetyl coenzyme A (CoA), thiolase, or 3-hydroxy-3-methylglutaryl CoA (HMGCoA) synthase was detectable at the different stages examined. Minimal levels of 114C-acetate incorporation into cholesterol and HMGCoA reductase activity were present at 16 days of fetal development in newborn and suckling rats, whereas both parameters increased rapidly before birth. The pattern of NaF nonsuppressible reductase activity showed a different activation state of the enzyme, suggesting the appearance of a modulation state, probably related to the development of some short-term regulatory mechanisms.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041180112
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  • 7
    Electronic Resource
    Electronic Resource
    Hormonal control of cholesterogenesis and related enzymes in isolated rat hepatocytes during pre- and postnatal development (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 125 (1985), S. 507-511 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The effect of glucagon and insulin on the incorporation of 1-14C-acetate into cholesterol and fatty acids and on the enzymes involved in the first steps of cholesterol synthesis (3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, 3-hydroxy-3-methyl-glutaryl-coenzyme A synthase, and acetoacetyl-coenzyme A thiolase) was investigated. Isolated rat hepatocytes at different stages of fetal and postnatal development were employed. Data obtained show the appearance of hormonal control on the 18th day of fetal life, indicating the same pattern, as regards acetate incorporation and HMGCoA reductase prepared and assayed in the presence of NaF. On the contrary, HMGCoA reductase, prepared without NaF, HMGCoA synthase, and acetoacetyl CoA thiolase, does not appear to respond to hormonal stimulation. In the perinatal period, the hormonal effect is no longer detectable, probably because of a hormone resistance of this metabolic pathway.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041250321
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  • 8
    Electronic Resource
    Electronic Resource
    Regulation of amino acid transport in isolated rat hepatocytes during development (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 130 (1987), S. 103-110 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The effect of amino acid depletion or supplementation and the effect of glucagon and insulin on the amino acid transport mediated by system A were investigated by determining the uptake of either 2-amino [1-14C]isobutyric acid (AIB) or N-methyl 2-amino [1-14C]isobutyric acid (MeAIB) in rat hepatocytes, freshly isolated at different stages of pre- and postnatal development. The data obtained show that the Na+-dependent uptake was higher at the earliest developmental stages, and steadily decreased until the adult level. The hormones increased AIB and MeAIB uptake enhancing the Vmax, while the Km was unchanged. This effect was evident in cells from adult and 18-20-day-old fetuses, while no response was present before the 18th day of fetal life and in the perinatal period. Actinomycin D or cycloheximide abolished this hormone-dependent increase. A decrease in AIB and MeAIB transport after incubation in an amino acid-rich medium was demonstrated at all ages tested, but was particularly evident in the prenatal life. The increase in the activity of the system following amino acid starvation was shown to be mostly dependent from de novo protein synthesis in the fetal life; on the contrary in the adult the increase appeared to be more linked to the releas from transinhibition of the transport.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041300115
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  • 9
    Electronic Resource
    Electronic Resource
    Adenosine potentiates forskolin-induced delay of meiotic resumption by mouse denuded oocytes: Evidence for an oocyte surface site of adenosine action (1988)
    New York, NY : Wiley-Blackwell
    Gamete Research 21 (1988), S. 157-168 
    Details
    ISSN: 0148-7280
    Keywords: oocyte ; meiotic resumption ; adenosine ; forskolin ; ATP ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Adenosine is present in the mouse follicular fluid and has been shown to interfere with oocyte maturation in vitro. To clarify the mechanism of adenosine action on meiotic arrest, we have characterized the synergistic action of this purine with forskolin on the meiotic resumption of mouse denuded oocytes.Forskolin delays meiotic resumption by approximately 1 hour; adenosine at concentrations ranging between 30-750 μM has no significant effect. Conversely, adenosine treatment together with forskolin produces a further delay in the resumption of meiosis. This adenosine effect is dose-dependent and mimicked by adenosine analogs like N6-phenylisopropyl adenosine (PIA), 2-chloroadensoine (2-CLA), 5′-N-ethylcarboxamide (NECA). Dipyridamole, which inhibits adenosine transport, does not prevent the meiosis-arresting synergistic effect of adenosine with forskolin. Adenosine causes a 50% increase of adenosine triphosphate (ATP) content in the oocyte. However, this increase is not directly responsible for the observed delay in the oocyte maturation for the following reasons: (1) the dose response of inhibition of meiotic resumption does not correlate with the doses of adenosine producing an increase in ATP; (2) dipyridamole blocks the increase in intracellular ATP, but it has no effect on the adenosine inhibition of maturation; (3) adenosine analogs inhibit oocyte maturation but do not affect intracellular ATP levels. These results suggest that the synergism of adenosine with forskolin on meiotic arrest does not require uptake of the nucleoside nor its conversion to ATP and that the adenosine effects are exerted at the level of the oocyte plasma membrane.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1120210206
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