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T Fehér

Publications and source records attributed to T Fehér.

At least 19 recordsLinked to original sources
PubMed2001

Anisotropy of superconducting MgB2 as seen in electron spin resonance and magnetization data.

We observed the conduction electron spin resonance (CESR) in fine powders of MgB2 both in the superconducting and normal states. The Pauli susceptibility is chi(s) = 2.0 x 10(-5) emu/mole in the temperature range of 450 to 600 K. The spin relaxation rate has an anomalous temperature dependence. The CESR measured below T(c) at several frequencies suggests that MgB2 is a strongly anisotropic superconductor with the upper critical field, H(c2), ranging between 2 and 16 T. The high-field reversible magnetization data of a randomly oriented powder sample are well described assuming that MgB2 is an anisotropic superconductor with H(ab)(c2)/H(c)(c2) approximately 6-9.

Journal Article↗
PubMed2000

Magnetic-field-induced low-energy spin excitations in YBa(2)Cu(4)O(8) measured by high field Gd(3+) electron spin resonance.

We have measured the spin susceptibility, chi(s), of the CuO(2) planes in the underdoped high T(c) superconductor, YBa(2)Cu(4)O(8) by Gd(3+) electron spin resonance (ESR) in single crystals and aligned powders in fields up to 15.4 T. At low temperatures and high fields, chi(s) is enhanced slightly in the B parallel c orientation with respect to the B perpendicular c orientation. The enhancement at 15.4 T (approximately equal to 0.15H(c2)) at 16 K (0.2 T(c)) is small: approximately 10% of chi(s)(T(c)), suggesting that the second critical field of superconductivity, H(c2) approximately equal to 100 T, would not suppress the pseudogap. This work demonstrates the potential of high field ESR in single crystals for studying high T(c) superconductors.

Journal Article↗
PubMed2000

Apoptosis of murine thymocytes induced by extracellular ATP is dose- and cytosolic pH-dependent.

Thymocytes from young Balb/C mice responded to low extracellular ATP (ATPec) doses (< or = 0.3 mM) with a rapid intracellular acidification (mean pH: ca. 0.3 pH unit) that was inhibited by the Ca2+ channel blocker verapamil, or by suramin (50 microM) and TNP-ATP (40 microM), potent P2x (and P2y) purinoreceptor antagonists. ATPec also triggered a remarkable DNA fragmentation and cell shrinkage detectable only at these low doses. DNA fragmentation gradually disappears with increasing [ATPec] above 0.5 mM, with a concomitant dominance of cytosolic alkalinization of the cells. Suramin and TNP-ATP also blocked the ATPec-triggered DNA fragmentation efficiently. oATP, inhibitor of P2z nonspecific ATP-gated membrane pores, and 2 mM extracellular Mg2+ did not influence either the cytosolic acidification or the DNA fragmentation, but almost completely abolished the intracellular alkalinization characteristic of P2z receptor activation at high ATPec doses. Antagonist-sensitivity of the ATPec-induced membrane potential responses indicates that hyperpolarization is associated with intracellular acidification, while rapid depolarization is linked to alkalinization. These data together indicate that the Ca2+-dependent hyperpolarization and cytosolic acidification triggered by low ATPec doses are essential early signals in apoptosis of murine thymocytes and are likely mediated by P2x1 type ATP-gated ion channels. Subset specificity of the early purinergic signals suggests that the double positive thymocytes are most sensitive to ATPec showing both P2z and P2x receptor activation characteristics, the double negative thymocytes preferentially show P2z-type, while single positive (CD4- CD8+ or CD4+ CD8-) thymocytes respond mostly by weaker P2x-type changes, indicating that ATPec, similarly to adenosine may serve as a potential regulator of cell death and differentiation in the thymus.

Adenosine Triphosphate↗
PubMed1998

Steroid hormone (hydrocortisone, oestradiol and testosterone) uptake, storage or induced synthesis in tetrahymena.

After cyclodextrin-coated 10(-6) m steroid hormone treatment for 3 days (hormonal imprinting), Tetrahymena cells and their media were analysed by radioimmunoassay for the same hormone and for the presence of the other two. In the absence of hormone treatment, the cells contained no detectable levels of the three steroids. By 2 days in fresh medium following exposure of cells to a 72 h pretreatment of each specific hormone, correspondingly high quantities of hydrocortisone and oestradiol, but lesser quantities of testosterone, were found in both the media and the cells. One week after treatment only traces of hydrocortisone were found, exclusively within the cells themselves. Oestradiol was present in measurable quantities in both cells and media, whereas testosterone was only present in the medium. The presence of the other two hormones to the one used in the pretreatment were not usually present, except that when testosterone had been given, some oestradiol was also detected at 48 h, suggesting Tetrahymena has a functional cytochrome P(450)aromatase.

Animals↗
PubMed1998

Relationship between blood pressure variability and serum dehydroepiandrosterone sulfate levels.

Decreased diurnal blood pressure variability and low dehydroepiandrosterone sulfate (DHEAS) levels are important predictors of cardiovascular morbidity and mortality. The aim of the study was to determine the relationship between DHEAS levels and diurnal blood pressure variability in normotensive subjects and in patients with essential hypertension of both genders. An ambulatory blood pressure monitor (ABPM), Meditech O2 device and radioimmunoassay were used for ambulatory blood pressure monitoring and the determination of DHEAS levels, respectively. A close correlation (P < .001) was found between the diurnal indices and plasma DHEAS levels of the 387 subjects (86 normotensive and 301 hypertensive patients) participating in the study. Decreased plasma DHEAS levels were associated in both genders, and in both normotensive and hypertensive patients with significantly (P < .001) lower diurnal indices. There was a close correlation (P < .001) between the age-related decrease in plasma DHEAS levels and diurnal indices in both genders. Systolic and diastolic blood pressure variability changed parallel to plasma DHEAS levels in both genders, whether hypertension was present or not. Additional investigations are needed to find out whether reduced DHEAS levels play a role in decreased diurnal indices or whether both can be traced back to one and the same cause.

Adult↗
PubMed1997

Reduction of stress-induced changes in meat quality with thermolysed brewer's yeast of high nucleotide content in pigs.

The effect exerted by a biogenic performance enhancer of high nucleotide content on meat quality in 20 Norwegian Landrace pigs (90 to 95 kg) was examined. The diet of the treated group was supplemented with the performance enhancer for the last 30 days of fattening. The stress effect was transport to the slaughterhouse and slaughter itself. Plasma creatine kinase (CK), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) activities, glucose and cortisol concentrations, and muscle pH were determined. Serious stress damage was found in the cardiac and skeletal muscle, as indicated by the high CK (980 U/L), LDH (> 1600 U/L) and AST (67 U/L) activities in the untreated group; values were significantly lower in the experimental pigs (458, 468 and 17 U/L, respectively). There were no significant differences in glucose and cortisol concentrations between the two groups. In the control group the pH values were significantly lower and more muscle samples showed PSE character than in the treated group (75 and 30%, respectively).

Animals↗
PubMed1996

[Clinical value of dehydroepiandrosterone and its sulfate ester].

The biological function of the since more than 5 decades discovered adrenal dehydroepiandrosterone and dehydroepiandrosterone sulphate we were studied since 1960. A renaissance of these steroids is talking about in last years. The knowledge of the metabolic features and biological effects of the hormone pair has been indispensable for internal, gynecologic and pediatric medicine, as well as for oncologists and immunologists. The present review summarizes our contemporary knowledge on the hormone pair in view of observations reported in the literature and made in our Institute. Recently, Professor Baulieu working in Paris, hypothesized that the supplementation of the gradual physiological decrease of dehydroepiandrosterone sulphate during aging processes may delay the biological events of aging. This may result in an improvement of "the general state of health, brighter and more care-free declining years".

Aged↗
PubMed1996

Effects of joining peptide (1-18) and histamine on dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS) production of human adrenocortical cells in vitro.

Joining peptide 1-18 (JP 1-18), added alone in concentrations of 10(-13)-10(-7) M to collagenase-dispersed human adrenocortical cells, did not affect the basal production of corticosterone, cortisol, aldosterone, dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS). JP 1-18 potentiated the ACTH-stimulated production of steroids. When administered in combination with histamine (10(-8)-10(-3) M), JP 1-18 (10(-8) or 10(-10) M), enhanced the synthesis of DHEA and DHEAS. JP 1-18, together with histamine, may play a role in the regulation of DHEA and DHEAS production.

Adrenal Cortex↗
PubMed1996

Comparison of some blood parameters of captured and farmed red deer (Cervus elaphus) hinds.

In studies on the adaptation of red deer (Cervus elaphus) to farm conditions, some blood parameters of 3- to 9-year-old captured and farmed hinds were compared. The test variable included blood plasma creatine kinase (CK), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) activities, the concentrations of glucose, urea, total protein (TP), serum cortisol, haemoglobin (Hb), and the blastogenic transformation of lymphocytes upon stimulation by the nonspecific mitogens Phaseolus vulgaris (PHA) and Concanavalin A (ConA) in the lymphocyte stimulation test (LST). The effects exerted by probiotic preparation (Ascogen) on the same parameters were studied in farmed deer. In hinds that had been kept under farm conditions for 10 months, CK activity was lower (P < 0.05) and blood urea concentration higher (P < 0.001) than at the time of capture, while their blood glucose concentration exceeded (P < 0.01) that of farmed hinds. Hinds treated with Ascogen had lower ALT activity (P < 0.001) and showed a higher increase in PHA-induced blastogenic transformation of lymphocytes than the control hinds.

Adaptation, Physiological↗
PubMed1994

Dehydroepiandrosterone sulphate and bone mineral density.

Several series of data suggest that alterations in adrenal androgen output might be a contributing factor to changes in bone mass. To study the possible relationship between bone density and serum levels of dehydroepiandrosterone sulphate (DHEAS) we investigated 105 women (aged 45-69 years; 76 postmenopausal, 29 perimenopausal). The patients were divided into two groups according to the bone mineral density (BMD) measurement (normal density n = 50, low density n = 55). BMD was measured by dual-energy X-ray absorptiometry of the lumbar spine and femoral neck. Bone mineral content (BMC) of the radius midshaft was measured by single photon absorptiometry. Serum DHEAS level was significantly lower in the 'low density' group than in the 'normal' one (1.91 +/- 1.04 v 4.77 +/- 2.03 mumol/l, p < 0.001). The serum DHEAS level decreased significantly with age in both groups (r = 0.43, p < 0.001 in the 'normal' group; r = 0.35, p < 0.01 in the 'low density' group). Unlike the slopes, the positions of the regression lines differed significantly (difference 2.85 mumol/l, p < 0.001). Correcting for age by multiple linear regression we established a significant positive relationship between DHEAS and BMD of the lumbar spine and femoral neck, and BMC of radius midshaft as well. Since there was no significant difference between the two groups regarding oestrogens, we suggest that DHEAS may have a non-oestrogenic effect on bone. The odds ratio of a subject with a low (< 3.3 mumol/l) serum DHEAS level having low BMD was 40 (confidence interval 13-126).(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1994

Dehydroepiandrosterone, dehydroepiandrosterone sulphate, and their relation to cortisol in red deer (Cervus elaphus).

Adrenal androgens, dehydroepiandrosterone, its sulphate and, in comparison, cortisol in serum were determined over two periods in red deer. The hormone levels were determined in hinds farmed from their births, captured in adulthood, and in fawns reared under farm conditions with their mothers or under artificial farm conditions without their mothers. In addition, steroid levels were studied in stags under farm conditions in and after the breeding season. Investigation of animals for their potential as farmed animals gave information on the stress susceptibility. It is suggested that the present assessment of hormonal events will provide prognostic information on their adaptation to farm conditions, reproductive performance, and possibly, their immune responses and the quality of their products.

Adrenal Glands↗
PubMed1992

Serum progesterone, oestrone and oestradiol in pregnant and non-pregnant red deer hinds.

Changes in serum progesterone (P), oestrone (E1) and oestradiol (E2) concentrations were monitored in 34 female red deer (Cervus elaphus) shortly after the end of the breeding season and at mid-gestation. Pregnancy could be detected on the basis of serum P, but there were no significant differences between the pregnant and non-pregnant animals farmed animals in E1 and E2 concentrations. Twenty-five pregnant hinds captured in winter showed serum P levels similar to those found in farmed deer during the gestation period.

Animals↗
PubMed1991

[Dehydroepiandrosterone and dehydroepiandrosterone-sulfate content of the amniotic fluid].

Steroid hormone determinations have been performed in amniotic fluid obtained by amniocentesis in 16 to 20 weeks of pregnancy utilizing our radioimmunological methods. Sporadic estimations reported in the literature were completed with our results of dehydroepiandrosterone (D) and dehydroepiandrosterone sulphate (DS) measurements obtained in relatively great number of cases. The observations allowed the early diagnosis of placental sulphatase deficiency. Study of this enzymopathy suggested that, in addition to oestrogens and progesterone, D and DS may have per se biological-hormonal effects for maturation processes in the intrauterine life. Furthermore, a hypothesis has been outlined for prenatal differential diagnostics of the congenital adrenal hyperplasia due to 3 beta-hydroxysteroid dehydrogenase deficiency.

Amniocentesis↗
PubMed1990

Hormonal regulation of complement biosynthesis in human cell lines--I. Androgens and gamma-interferon stimulate the biosynthesis and gene expression of C1 inhibitor in human cell lines U937 and HepG2.

C1 inhibitor (C1inh), a member of the serine protease inhibitor gene superfamily, is a glycosylated plasma protein inhibiting the proteolytic activities of C1r and C1s and involved in the regulation of coagulation, fibrinolysis and kinin-releasing systems. In this study, the in vitro effect of androgen hormones, dehydroepiandrosterone (DHEA), testosterone (TEST) and recombinant human gamma-interferon (gamma-IFN), has been determined on the production of C1inh in human cell lines. In both human monocytoid/histiocytoid cell line U937 and in hepatoma derived cell line HepG2, DHEA and TEST upregulated the gene expression and secretion of C1inh. The most pronounced effect was detected in the concn range 10(-7)-10(-9) M of the hormones. Under the same conditions DHEA and TEST had no detectable effect on the biosynthesis of C3, C2 and factor B by these cells, but DHEA at higher concn (10(-4) M) slightly increased that of C4 in HepG2 cells. Both in U937 and in HepG2 cells recombinant gamma-IFN markedly increased the gene expression and secretion of C1inh. This effect of gamma-IFN was abolished by histamine.

Carcinoma, Hepatocellular↗