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Biomedical subjects

M Szabo

Publications and source records attributed to M Szabo.

At least 37 records · Page 2Linked to original sources
PubMed1996

RU486 on an estrogen background blocks the rise in serum follicle-stimulating hormone induced by antiserum to inhibin or ovariectomy.

We used passive immunization with an antiserum to the alpha-subunit of inhibin (anti-I) or acute ovariectomy to investigate the relationship between serum inhibin levels and FSH secretion in the presence of the progesterone/glucocorticoid antagonist RU486. We demonstrated previously that 1) anti-I administered at 1700 h causes serum FSH to rise on the morning of estrus, even in the presence of a GnRH antagonist, when the two treatments are delivered on proestrus; and that 2) RU486 given on proestrus (1230 h), a time when serum estradiol levels are high, not only blocks the natural secondary FSH surge, but also suppresses the anti-I-induced rise in serum FSH on the morning of estrus. We have now extended our studies of the relationship between inhibin and RU486 to investigate treatment with RU486 and anti-I on a different day of the cycle, estrus, when serum estradiol levels are low. When both RU486 and anti-I were given on estrus (1230 and 1700 h, respectively), RU486 failed to block the anti-I-induced rise in serum FSH on the next morning of metestrus, in contrast to the blockade seen with RU486 treatment on the day of proestrus. However, pretreatment with estradiol benzoate (50 microgram) on the evening of proestrus, before the RU486 and anti-I treatment on estrus, caused RU486 to suppress the effects of anti-I on serum FSH, as it does when given on proestrus. We then repeated the study, using ovariectomy on proestrus or estrus (1700 h) to raise serum FSH, and assessed the effects of RU486 treatment at proestrus and estrus and estradiol benzoate treatment on proestrus. Our results indicate that treatment with RU486 can block the postovariectomy rise in serum FSH only in the presence of high circulating estradiol levels. We conclude that the inhibitory action of RU486 on FSH secretion after a fall in serum inhibin depends on a precedent estradiol background, probably due to induction of progesterone receptors by estradiol.

Animals↗
PubMed1996

Corticosterone selectively increases follicle-stimulating hormone beta-subunit messenger ribonucleic acid in primary anterior pituitary cell culture without affecting its half-life.

We demonstrated previously that glucocorticoids differentially affect the levels of the two pituitary gonadotropins, LH and FSH, both in vivo and in vitro. In vivo, the effect of glucocorticoids is GnRH independent, indicating a direct action on the gonadotrope, and it leads to selective up-regulation of the pituitary content of FSH and FSH beta-subunit messenger RNA (mRNA). The objective of the present study was to confirm the direct action of corticosterone (B) on FSH beta-subunit mRNA in primary anterior pituitary cell culture and to assess whether the selective B-induced rise in FSH beta mRNA is mediated through altered stability of the FSH beta transcript. Anterior pituitary glands collected from randomly cycling female rats were dissociated with trypsin. Cells were incubated at 37 C for 48 h and subsequently exposed to vehicle or B (1.7 microM) for an additional 42 h. At the end of the incubation, media were sampled for FSH and LH, cells were lysed, and total RNA was isolated for Northern blot analysis. Exposure to B for 42 h caused direct and selective upregulation of FSH release, FSH content, and FSH beta mRNA; decreased alpha-subunit mRNA; and had no significant effect on LH release, LH content, or LH beta mRNA. To evaluate the mRNA stability of the three subunits, cells were exposed to the transcription blocker actinomycin D (act D; 5 micrograms/ml) for an additional 6 h. The combined 6-h treatment with B and act D slightly, but significantly, suppressed alpha-subunit mRNA and did not change LH beta mRNA, confirming a long half-life of the two gonadotropin subunit mRNAs. In contrast, FSH beta mRNA was significantly suppressed by act D to the same level in vehicle- and B-treated cells. The posttranscriptional decay rate was examined by sampling at 0, 1, 2, 3, and 6 h during the 6-h act D treatment period. Decay curves for FSH beta mRNA were parallel in vehicle- and B-treated cells, indicating that B did not alter FSH beta mRNA stability. We conclude that the selective B-induced rise in FSH beta mRNA is mediated at the level of transcription rather than mRNA stabilization.

Animals↗
PubMed1995

Prolonged effects of tumor necrosis factor-alpha on anterior pituitary hormone release.

We examined the chronic (72 h) effects of 30 ng/ml recombinant murine tumor necrosis factor (TNF)-alpha on release of immunoreactive growth hormone (GH), prolactin (PRL), thyrotropin (TSH), and TSH glycosylation, as assessed by lectin binding, in cultured rat anterior pituitary cells. In cultured cells from adult female rats, TNF-alpha significantly suppressed basal and GH-releasing hormone (GRH)-stimulated GH release. TNF-alpha also suppressed basal PRL release and completely abolished the PRL response to TRH (0.1-10 nM). Whereas TNF-alpha reduced basal TSH release, it significantly enhanced the maximal TSH response to TRH. TNF-alpha did not affect the concanavalin A and lentil lectin binding of TSH accumulated in the medium during the 4-day culture, but significantly decreased the lentil lectin binding of TSH released in response to acute TRH stimulation. TNF-alpha significantly enhanced the inhibitory effect of somatostatin on stimulated PRL release, but not on GH or TSH release. Compared to cell cultures from adult female rats, in anterior pituitary cell cultures from 12-day-old rats the effects of prolonged exposure to TNF-alpha on hormone release were diminished or absent. Pituitary hormone release was unaffected by acute (3 h) exposure to TNF-alpha. These results demonstrate a direct effect of TNF-alpha on anterior pituitary hormone release, which is cell-type specific and age dependent.

Animals↗
PubMed1995

Relationships between rfb gene clusters required for biosynthesis of identical D-galactose-containing O antigens in Klebsiella pneumoniae serotype O1 and Serratia marcescens serotype O16.

The lipopolysaccharide O antigens of Klebsiella pneumoniae serotype O1 and Serratia marcescens serotype O16 both contain a repeating unit disaccharide of [-->3)-beta-D-Galf-(1-->3)-alpha-D-Galp-(1-->]; the resulting polymer is known as D-galactan I. In K. pneumoniae serotype O1, the genes responsible for the synthesis of D-galactan I are found in the rfb gene cluster (rfbKpO1). We report here the cloning and analysis of the rfb cluster from S. marcescens serotype O16 (rfbSmO16). This is the first rfb gene cluster examined for the genus Serratia. Synthesis of D-galactan I is an rfe-dependent process for both K. pneumoniae serotype O1 and S. marcescens serotype O16. Hybridization experiments with probes derived from each of the six rfbKpO1 genes indicate that the cloned rfbSmO16 cluster contains homologous genes arranged in the same order. However, the degree of homology at the nucleotide sequence level was sufficiently low that hybridization was detected only under low-stringency conditions. rfbABSmO16 genes were subcloned and shown to encode an ABC-2 (ATP-binding cassette) transporter which is functionally identical to the one encoded by the corresponding rfb genes from K. pneumoniae serotype O1. The amino acid sequences of the predicted RfbA and RfbB homologs showed identities of 75.7% (87.9% total similarity) and 78.0% (86.5% total similarity), respectively. The last gene of the rfbKpO1 cluster, rfbFKpO1, encodes a bifunctional galactosyltransferase which initiates the formation of D-galactan I. RfbFKpO1 and RfbFSmO16 are 57.6% identical (with 71.1% total similarity), and both show similarity with RfpB, the galactosyltransferase involved in the synthesis of Shigella dysenteriae type I O-polysaccharide. The G+C contents of the rfbAB genes from each organism are quite similar, and values are lower than those typical for the species. However, the G+C content of rfbFSmO16 (47.6%) was much higher than that of rfbFKpO1 (37.3%), despite the fact that the average for each species (52 to 60%) falls within the same range.

ATP-Binding Cassette Transporters↗
PubMed1995

Autofeedback suppression of growth hormone (GH) secretion in transgenic mice expressing a human GH reporter targeted by tyrosine hydroxylase 5'-flanking sequences to the hypothalamus.

Transgenic mice expressing a tyrosine hydroxylase-human (h) GH fusion gene in the hypothalamus exhibit a dwarf phenotype. The GH feedback mechanism(s) underlying the growth retardation in these animals was investigated by assessing peptide and messenger RNA (mRNA) levels of the hormones of the hypothalamic-GH-IGF-I axis. Pituitary GH content, hypothalamic GH-releasing hormone (GHRH) and somatostatin (SRIH) content, and serum IGF-I levels were measured by RIA. mRNA levels of hypothalamic GHRH and SRIH and of pituitary GH and the GHRH receptor were measured by Northern blot hybridization. Transgenic mice of both sexes and their wild-type littermates were studied at 2-4 months of age. The pituitary GH content was markedly reduced by 85% in male and by 87% in female transgenic mice compared to that in wild-type controls (P < 0.01 for both). The pituitary GH mRNA content was also decreased by 73% (P = 0.002) in transgenic male mice. Circulating IGF-I levels were significantly reduced by 66% and 68% in male and female transgenic mice, respectively (P = 0.001). The hypothalamic GHRH content was significantly reduced by 19% and 33% (P < 0.05) in male and female transgenic mice, respectively. No significant difference was detected, however, in the hypothalamic SRIH content between wild-type and transgenic mice. Hypothalamic GHRH mRNA levels were significantly decreased by 35% (P = 0.002) in transgenic male mice compared to those in wild-type littermates. In contrast, SRIH mRNA was not significantly changed. An even greater reduction (61%; P = 0.003) was observed in pituitary GHRH receptor mRNA in transgenic mice. These data indicate that the GH deficiency and dwarf phenotype of the tyrosine hydroxylase-hGH transgenic mouse can be attributed primarily to impaired hypothalamic GHRH production. The mechanism of GH feedback inhibition appears to involve direct suppression of GHRH gene expression by locally produced hGH in the hypothalamus.

Animals↗
PubMed1995

Ontogeny of the GH response to phorbol ester and phospholipase C in rat pituitary cells.

GH secretory patterns undergo marked change during early mammalian development. The factors that underlie these changes and the major components of signal transduction in the immature somatotrophs are not fully understood. Increasing evidence suggests that protein kinase C (PKC) plays a central role in perinatal organ differentiation and function. To evaluate the possible role of PKC as a mediator of GH secretion from immature pituitaries, we tested the effects of the PKC activating phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), alone or together with GH-releasing factor (GRF), somatostatin (SRIF), and Ca2+ modifying agents; an inactive phorbol analogue (4 alpha-12-13-didecanoate; 4 alpha-PDD), and phospholipase C on GH release from pituitary cell cultures from perinatal and mature rats. Pituitary primary cell cultures were prepared from fetal (day 20 of 21.5 days of gestation), 2-day-old, 12-day-old, and adult male (2- to 4-month-old) rats. Each experiment was performed on at least three separate occasions. The magnitude of TPA (0.15-150 nM)-induced GH release was markedly age-dependent, fractional GH release being greatest from pituitaries of fetal and newborn rats, and least from those of adults (P < 0.001). Further, the minimum dose of TPA required to stimulate GH release over basal levels was tenfold higher for adult pituitaries (15 nM) than for perinatal pituitaries (1.5 nM). Phospholipase C (1 and 10 U/ml) also caused greater fractional GH release from neonatal pituitaries than from adult pituitaries (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

DNA regulatory sequences of the rat tyrosine hydroxylase gene direct correct catecholaminergic cell-type specificity of a human growth hormone reporter in the CNS of transgenic mice causing a dwarf phenotype.

Transgenic mice bearing 4.8 kilobases (kb) of upstream rat tyrosine hydroxylase (TH) sequences linked to a human growth hormone gene (hGH) exhibited cell-specific expression of hGH in all the appropriate catecholaminergic neurons in the central nervous system (CNS), although with different penetrance in two different mouse lineages. No ectopic expression was observed in any brain or peripheral region in one founder and its progeny. In another founder there was some ectopic expression in addition to appropriate and high levels of tissue-specific expression in all catecholaminergic areas. These results identify regulatory sequences that are sufficient for targeting expression to all catecholaminergic CNS neurons. Also, expression of exogenous hGH in the hypothalamus caused a dwarf phenotype, generating a novel genetic model for GH deficiency of hypothalamic origin.

Aging↗
PubMed1993

The effect of isobutylmethylxanthine, forskolin, and cholera toxin on growth hormone release from pituitary cell cultures of perinatal and mature rats.

The factors that regulate growth hormone (GH) release during the perinatal period are not well understood. Circulating GH levels are markedly elevated in mammalian fetuses and newborns compared with mature animals, and the immature pituitary is highly responsive to the GH-stimulatory effect of GH-releasing factor (GHRF). The etiology of these developmental changes in GH secretion is not known. In order to investigate the mechanisms underlying GH release from immature pituitaries, we tested the effects of agents that increase intracellular cyclic adenosine 3',5' monophosphate (cAMP) production independent of the GHRF receptor on GH release from pituitaries of developing and mature rats. Pituitary cell cultures from fetal (day 20 of gestation), newborn (postnatal day 2), juvenile (postnatal day 12-15), adult male (3-4 months), and adult female (3-4 months) rats were tested with isobutylmethylxanthine (IBMX; 0.001-1.0 mM), forskolin (0.01-10 microM), and cholera toxin (0.025-25 ng/ml). IBMX, forskolin, and cholera toxin stimulated GH release in a dose-dependent manner from pituitary cultures of all age groups. However, the magnitude of the GH responses to these agents was highly age-dependent. Perinatal pituitaries exhibited markedly greater GH responses to IBMX, forskolin, and cholera toxin than did those of mature animals (P < 0.001 for age effect with each agent). GH release in response to the highest dose of IBMX (1 mM) was 301 +/- 8, 389 +/- 37, 296 +/- 33, 198 +/- 14, and 187 +/- 19% of control values from pituitary cell cultures of fetal, newborn, juvenile, adult male, and adult female rats, respectively (P < 0.001). In response to the highest dose of forskolin (10 microM) GH release was 537 +/- 46, 601 +/- 75, 274 +/- 22, 270 +/- 37, and 248 +/- 35% of control values in the same respective age groups (P < 0.001). Similarly, the highest dose of cholera toxin (25 ng/ml) stimulated GH release to 407 +/- 55, 365 +/- 43, 249 +/- 26, 186 +/- 11, and 186 +/- 1% of controls in these respective age groups (P < 0.003). The marked stimulation of GH release from perinatal pituitaries by IBMX, forskolin, and cholera toxin is consistent with the concept that cAMP is a potent mediator of GH release from immature as well as mature somatotrophs. The developmental changes in the GH secretory response to these agents further suggest that signal transduction pathways mediating GH release may undergo maturation, at least in part, at intrasomatotroph loci distal to the GHRF receptor.

1-Methyl-3-isobutylxanthine↗
PubMed1992

Use of chromosomal gene fusions to investigate the role of repetitive DNA in regulation of genes involved in lipopolysaccharide biosynthesis in Haemophilus influenzae.

The lic3 locus of Haemophilus influenzae consists of four open reading frames. The derived amino acid sequences of orf2 and orf4 exhibit homology to Escherichia coli GalE and AdK, respectively. The functions of orf1 and orf3 remain unknown. orf1 contains multiple tandem repeats of the tetrameric DNA sequence CAAT near the 5' end. Two possible translational starts (ATG1 and ATG2) lie upstream. We have used lacZ fusions to investigate whether changes in the number of CAAT repeats in conjunction with differential usage of the upstream frames control the expression of lic3-orf1. Phase-variable expression of lacZ was observed for individual colonies and could be related to variable numbers of CAAT repeats. Of the three possible upstream frames, only one, containing the more downstream of the two possible ATG start codons (ATG2), is used for strong expression of lacZ. Utilization of the more upstream ATG (ATG1) or ATG2 was observed with medium-level expression, while utilization of any of the three possible frames was observed when lacZ was expressed at low to undetectable levels, indicating that other mechanisms may affect expression. To investigate this, lacZ was fused in frame with ATG2 of lic3-orf1, with concomitant deletion of the repeats. Phase-variable expression was still observed, supporting the view that an alternative level of control operates in conjunction with the repeat mechanism.

Amino Acid Sequence↗
PubMed1991

In vitro cytotoxicity of Haemophilus influenzae lipopolysaccharides for bovine aortal endothelial cells.

The cytotoxicity of purified lipopolysaccharide (LPS) from a prototype Haemophilus influenzae type b (Hib) strain (Eagan) and three transformants, differing in their LPS phenotype, for bovine aortal endothelial cells (BAOEC) was investigated. All LPS preparations caused cell disruption and release of lactate dehydrogenase (LDH), an indicator of cytotoxicity, from BAOEC monolayers but to differing extents. There was no correlation between the cytotoxicity of purified Hib LPS to BAOEC monolayers and potential to cause bacteraemia in experimental animals.

Animals↗
PubMed1990

Biphasic action of forskolin on growth hormone and prolactin secretion by rat anterior pituitary cells in vitro.

To assess the role of cAMP-mediated signal transduction processes in mediation of secretagogue-stimulated GH release, we examined the dose-related effects of the diterpene adenylate cyclase activator forskolin (FSK) in primary monolayer cultures of rat adenohypophyseal cells. In cell cultures prepared from both immature (12 days old) and adult (6 weeks to 4 months old) male or female rats, the dose-related stimulation of GH release by FSK was biphasic. With increasing FSK concentrations from 0.03-3.16 microM, GH release increased progressively to maximal values of 442 +/- 19% and 303 +/- 10% of basal release in cells from immature and adult rats, respectively. FSK concentrations above 3.16 microM induced progressively diminished GH responses, with net inhibition to below basal release evident at 100 microM FSK. FSK stimulated PRL release to a lesser degree than it did GH release; the PRL response to FSK was also biphasic. When maximal stimulatory concentrations (Emax) of FSK and GH-releasing factor (GRF; 10 nM) were added in combination, the GH response was significantly less than the individual response to either secretagogue alone. In response to FSK alone, GRF alone, and FSK plus GRF, GH release was 478 +/- 7%, 583 +/- 11%, and 244 +/- 5%; 278 +/- 4%, 283 +/- 3%, and 175 +/- 2%; and 299 +/- 12%, 351 +/- 5%, and 191 +/- 17% of basal release in cells from 12-day-old, adult male, and adult female rats, respectively (P less than 0.01 for all responses to combined addition vs. the individual responses). Submaximal stimulatory concentrations of GRF added in combination with submaximal FSK elicited partially additive GH responses; the GH response to Emax GRF, on the other hand, was inhibited in a dose-related manner by all concentrations of FSK that by themselves were stimulatory. The GH responses were also suppressed when Emax FSK was added to cultured cells of 12-day-old rats in combination with Emax cholera toxin (2.5 ng/ml) or prostaglandin E2 (10 microM), agents whose actions, like that of GRF, involve adenylate cyclase activation. In contrast, FSK did not suppress but in most cases augmented the maximal GH responses to secretagogues whose action is independent of adenylate cyclase activation: (Bu)2cAMP (0.5 mM), TRH (100 nM), phorbol myristate acetate (50 nM), the Ca2+ ionophore A23187 (250 microM), and the dihydropyridine Ca2+ channel agonist BAY K8644 (10 microM). Indeed, combined addition of FSK with the latter two agents resulted in synergistic stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

The importance of fiberbronchoscopy in respiratory burns.

Respiratory burns worsen considerably the prognosis of the patients. Fiberoptic endoscopy facilitated the examination of respiratory burns and determined the degree and extent of mucosal damage. At the same time, aspiration and lavage of the affected bronchi can be advantageously used in therapy. 22 patients with respiratory burns were hospitalized at the Burn Centre, Works Institute of Health Care, East Slovak Iron Works, Kosice (Czechoslovakia); 13 of them died, i.e. 59.1%. The paper analyzes fiberbronchoscopy applied to respiratory burns, anaesthetic technique and intubation, and the results are compared with post mortem findings. Some clinical findings are demonstrated, too.

Bronchoscopy↗
PubMed1989

The effect of age on prostaglandin E2 stimulation of growth hormone release from cultured rat pituitary cells.

Prostaglandin E2 (PGE2) is a potent secretagogue of GH in mature mammals. Although PGs are produced by the fetus and newborn of many species, the ontogeny of PGE2's GH stimulatory effect and the interaction of PGE2 with GHRF in the developing animal are not known. We examined the effects of 0.01-10 microM PGE2 and 0.01-10 nM rat GHRF, alone and in combination, on GH release from cultured pituitary cells of 2-day(d)-old, 7-d-old, 15-d-old, and adult (3- to 4-month-old) male rats (n = 4-7 experiments/age group). The effect of PGE2 on GH release was markedly age dependent. The GH response to all doses of PGE2 over 0.01 microM was greatest in pituitary cells of adult and 15-d-old rats and least in those of 2-d-old pups. PGE2 (0.1 microM) did not cause significant GH release from pituitary cells of 2-d-old pups (110 +/- 3% of control values), but increased that from 7-d-old, 15-d-old, and adult pituitary cells to 126 +/- 8%, 155 +/- 8%, and 156 +/- 9% of respective control values (by analysis of variance: F = 7.28; P less than 0.001). PGE2 (1 microM) increased GH release to 123 +/- 8%, 145 +/- 12%, 259 +/- 24%, and 260 +/- 17% of control values from pituitary cells of these same respective age groups (F = 12.3; P less than 0.001). The highest dose of PGE2 studied (10 microM) yielded similar results. The influence of PGE1 on GH release was also age dependent and similar to that of PGE2. In contrast to PGE2, GHRF stimulated GH release most in pituitary cells of 2-d-old pups and least in those of adults, similar to our previous observations with human GHRF-40. Coincubation with PGE2 and low dose GHRF resulted in partial additivity of GH response in adult rats, but no additivity in newborn pups. These results indicate that in rats, the sensitivity of the somatotroph to PGE2 increases with advancing age after birth. The contrasting developmental patterns of somatotroph sensitivity to PGE2 and GHRF support the concept that these GH secretagogues act, at least in part, by different intracellular mechanisms, which are subject to differential rates of maturation.

Animals↗
PubMed1988

Impaired suppression of growth hormone release by somatostatin in cultured adenohypophyseal cells of spontaneously diabetic BB/W rats.

The effects of the diabetic state on the somatotroph's responsiveness to the secretagogues GRF and (Bu)2-cAMP and to the inhibitor somatostatin (SRIF) were evaluated in enzymatically dissociated rat adenohypophyseal cells in primary monolayer culture. Primary cultures were prepared from pituitary tissue of spontaneously diabetic BB/W rats 23-51 days after the onset of hyperglycemia and glycosuria and of age-matched diabetes-resistant control rats. Dose-related stimulation of GH release by GRF and (Bu)2cAMP did not differ significantly in the two preparations. There was no evidence of abnormal sensitivity to TRH in cultured somatotrophs of diabetic rats. Dose-related suppression of (Bu)2cAMP (0.5 mM)-stimulated GH release by 0.01-10 nM SRIF, on the other hand, was significantly affected by diabetes, as indicated by a parallel shift of the dose-response curve to the right and an increase in the IC50 value from 76 +/- 2 to 204 +/- 5 pM (mean +/- SEM; n = 3; P less than 0.001). Maximal suppression by 10 nM SRIF was identical in the two preparations. The degree to which the cultured cells' responsiveness to SRIF was reduced was unrelated to the duration and severity of the diabetic state. Hypothalamic SRIF content did not differ significantly between diabetic and diabetes-resistant rats (186 +/- 12 vs. 178 +/- 10 ng/mg protein). Nevertheless, the SRIF concentration may be elevated in hypophysealportal blood of diabetic rats; we, therefore, examined the effect of prolonged exposure of the cell cultures to SRIF or SMS 201-995 on the subsequent suppression of (Bu)2cAMP-stimulated GH release by SRIF. Addition of either SRIF (10 nM) or SMS 201-995 (5.5 nM) to the culture medium for 4 days significantly increased the IC50 values for SRIF to values similar to those obtained in cultured cells of diabetic rats. We conclude that the somatotrophs of diabetic rats are relatively resistant to SRIF. Since prolonged exposure to SRIF in vitro produced similar resistance, the desensitization in diabetic rats may be due to elevated concentrations of SRIF in hypophyseal-portal blood. This impaired responsiveness to SRIF may contribute to aberrant GH secretion in diabetes.

Animals↗