Biomedical subjects

B Hoffmann

Publications and source records attributed to B Hoffmann.

At least 163 records · Page 9Linked to original sources

PubMed1990

Agonist-sensitive binding of a photoreactive GTP analog to a G-protein alpha-subunit in membranes of HL-60 cells.

Myeloid-differentiated HL-60 cells were used to study the activation of G-proteins by receptor agonists. Following incubation of membranes with the photoreactive GTP analog. [alpha-32P]GTP azidoanilide, and subsequent exposure to ultraviolet light (254 nm), photolabeling of 40 kDa proteins comigrating with the Gi2 alpha-subunit was observed. Photolabeling in the absence or presence of the chemoattractant, N-formyl-methionyl-leucyl-phenylalanine (FMLP), absolutely required Mg2+; FMLP stimulated photolabeling at all Mg2+ concentrations employed (up to 30 mM). Addition of GDP (3-50 microM) reduced basal photolabeling to a greater extent than photolabeling stimulated by FMLP. FMLP did not stimulate photolabeling of proteins modified by pertussis toxin. Leukotriene B4 and C5a also stimulated photolabeling of 40 kDa proteins. The results indicate that (i) the major G-protein in HL-60 cells, Gi2, requires Mg2+ for basal and receptor-stimulated activity, (ii) effective receptor-mediated activation of G-proteins is observed at mM concentrations of Mg2+, and (iii) receptor agonists apparently reduce the affinity of G-proteins for GDP.

Affinity Labels↗

PubMed1990

Basic fibroblast growth factor and transforming growth factor-alpha are hepatotrophic mitogens in vitro.

Basic fibroblast growth factor (bFGF) and transforming growth factor-alpha (TGF alpha) have been identified as potent hepatotrophic mitogens. bFGF and TGF alpha induce DNA synthesis in fetal and adult rat hepatocytes in primary culture and support fetal rat hepatocyte multiplication in chemically defined medium. No additional exogenous growth or progression factors are required by the cells for traversing the cell cycle or for cell division. These mitogenic polypeptides, previously identified in various cell types including liver and endothelial cells, platelets, and macrophages may act locally in a paracrine mode in controlling hepatocyte multiplication in the liver during development and regeneration.

Animals↗

PubMed1990

Precocious induction of tyrosine aminotransferase mRNA by hydrocortisone in cultured fetal rat hepatocytes at different developmental stages.

Tyrosine-aminotransferase (TAT) is encoded by a liver-specific gene known to be expressed perinatally. Fetal rat hepatocytes (gestation day 19) in primary cultures, in which TAT gene expression is normally undetectable, are induced by hydrocortisone to express TAT-mRNA in a dose-dependent manner (greater than 10(-7) M). In hepatocytes incubated with hydrocortisone, TAT-mRNA levels were marginal after 24 hours, reaching maximal levels at 48 hours. After a pre-incubation of hepatocytes for 24 hours in the absence of hydrocortisone followed by exposure to hydrocortisone (24-48 hours). TAT-mRNA levels were high. Hepatocytes derived from fetuses of gestation days 14 and 17 displayed comparable levels of TAT-mRNA in response to hydrocortisone. These results demonstrate that cultured hepatocytes of gestational stages as early as day 14, which initially do not respond to hydrocortisone by TAT gene induction, undergo a "maturation" process during the initial 24 hours following cultivation, resulting in the acquisition of precocious competence for TAT gene transcription in response to hydrocortisone. This suggests that one or more factor(s), required for hydrocortisone-inducible TAT gene transcription, and not available in fetal liver until birth (Gluecksohn-Waelsch: Cell, 18:225-237, 1979) appear in fetal hepatocytes upon cultivation during this "maturation" period, thus permitting precocious TAT gene expression in vitro.

Animals↗

PubMed1990

Aldosterone regulates paracellular pathway resistance in rabbit distal colon.

Regulation of the paracellular pathway in rabbit distal colon by the hormone aldosterone was investigated in vitro in Ussing chambers by means of transepithelial and microelectrode techniques. To evaluate the cellular and paracellular resistances an equivalent circuit analysis was used. For the analysis the apical membrane resistance was altered using the antibiotic nystatin. Under control conditions two groups of epithelia were found, each clearly dependent on the light: dark regime. Low-transporting epithelia (LT) were observed in the morning and high-transporting epithelia (HT) in the afternoon. Na+ transport was about 3-fold higher in HT than in LT epithelia. Incubating epithelia of both groups with 0.1 mumol.l-1 aldosterone on the serosal side nearly doubled in LT epithelia the short circuit current and transepithelial voltage but the transepithelial resistance was not influenced. Maximal values were reached after 4-5 h of aldosterone treatment. In HT epithelia due to the effect of aldosterone all three transepithelial parameters remained constant over time. Evaluation of the paracellular resistance revealed a significant increase after aldosterone stimulation in both epithelial groups. This increase suggests that tight junctions might have been regulated by aldosterone. The hormonal effect on electrolyte transport was also dependent on the physiological state of the rabbit colon. Since net Na+ absorption in distal colon is, in addition to transcellular absorption capacity, also dependent on the permeability of the paracellular pathway, the regulation of tight junctions by aldosterone may be a potent mechanism for improving Na+ absorption during hormone-stimulated ion transport.

Aldosterone↗

PubMed1990

A retinoic acid receptor-specific element controls the retinoic acid receptor-beta promoter.

The morphogen retinoic acid (RA) regulates gene transcription by interacting with specific nuclear receptors that recognize DNA sequences near responsive promoters. While much has recently been learned about the nuclear receptor proteins, little is known about the genes that are directly regulated by RA and their cis-acting response elements recognized by these receptors. Here we have analyzed the RA receptor-beta (RAR beta) gene promoter that is controlled by RA. We find that a RA-responsive element (RARE) is located adjacent to the TATA box. The RARE shows a direct repeat symmetry which is essential for its function. While thyroid hormone-responsive elements can also function as RAR response elements, we show here that this RARE is activated by endogenous RARs and RAR beta, but cannot be regulated by thyroid hormone receptors and other known nuclear receptors. In addition, we find that RAR gamma is a poor activator of this RARE. However, the response element is bound with high affinity by both RAR beta and RAR gamma as well as by thyroid hormone receptors. Thus, interaction between specific response elements and receptors is insufficient for gene activation.

Base Sequence↗

PubMed1990

[Histamine poisoning following consumption of fried fish].

Cases of food poisoning after consumption of fried fish in marinades are often caused by increased content of histamine. From 1973 to 1988 28 outbreaks in groups of persons with symptoms of histamine poisoning were analysed in the district of Dresden (GDR). The content of histamine most commonly exceeded the tolerance limit of 300 mg/kg fried fish.

Animals↗

PubMed1990

[The diagnosis of adrenal cortical function in animals using hormone analysis].

This paper describes the use of hormone analysis in the diagnosis of adrenal cortex dysfunction in the dog, cat and horse. Analytical problems concerning the determination of corticosteroid levels are discussed and the pathology of adrenal dysfunction is briefly presented. The paper focuses on the problems in establishing physiological norms for adrenal function based on the established assays. Own experiences and other reported data are referred to.

Adrenal Cortex Diseases↗

PubMed1989

Positive and negative control of nod gene expression in Rhizobium meliloti is required for optimal nodulation.

We show that expression of common nodulation genes in Rhizobium meliloti is under positive as well as negative control. A repressor protein was found to be involved in the negative control of nod gene expression. Whereas the activator NodD protein binds to the conserved cis-regulatory element (nod-box) required for coordinated regulation of nod genes, the repressor binds to the overlapping nodD1 and nodA promoters, at the RNA polymerase binding site. A model depicting the possible interaction of the plant-derived nod gene inducer (luteolin), the NodD and the repressor with the nod promoter elements is presented. Mutants lacking the repressor exhibited delayed nodulation phenotype, indicating that fine tuning of nod gene expression is required for optimal nodulation of the plant host.

Journal Article↗

PubMed1989

Establishment and partial characterization of SV40 virus-immortalized hepatocyte lines of normal and lethal mutant mice carrying a deletion on chromosome 7.

Deletions in chromosome 7 of the mouse have been shown to cause failure of expression of various hepatocyte-specific genes in newborn deletion homozygotes, including the gene encoding tyrosine amino transferase (TAT) (EC 2.6.1.5) (Gluecksohn-Waelsch, 1979). Primary liver cultures of newborn albino deletion mutant mice (c14CoS/c14CoS) and of phenotypically normal mice (c14CoS/cch or cch/cch) were infected with SV40 virus and multiplying hepatocytes selected in arginine-deficient medium containing epidermal growth factor (EGF), insulin, and hydrocortisone (HC). Resulting normal (NMH-ch) and mutant (NMH-m14) hepatocyte lines expressing integrated viral transforming sequences did not senesce, they multiplied autonomously of EGF in medium with insulin plus HC, and they retained hepatocyte-specific functions. Both lines synthesized arginine and contained albumin and alpha-fetoprotein (AFP) mRNAs. TAT-specific mRNA was detected in normal but not in mutant hepatocyte lines. A fragment of the mouse tyrosinase gene, known to map at the albino locus (c) within the region deleted in the c14CoS mutant, hybridized with a 2.5 kb EcoRI fragment of normal NMH-ch DNA, whereas this fragment was undetectable in mutant NMH-m14 DNA. These immortalized hepatocyte lines reflect important properties of normal and mutant liver tissues from which they were derived. The deletion mutant mouse cell lines may be useful for complementation studies involving sequences corresponding to the deletions that encode regulatory gene(s) involved in the control of inducible expression of certain hepatocyte-specific genes such as TAT.

Animals↗

PubMed1989

Proliferation of fetal rat hepatocytes in response to growth factors and hormones in primary culture.

Fetal rat hepatocytes (day 19 of gestation) multiply in primary culture in arginine-free, hydrocortisone-containing chemically defined medium MX-82 supplemented either with epidermal growth factor (EGF) or insulin or both. In contrast, hepatocytes did not multiply under similar culture conditions using Dulbecco's minimum essential medium (DMEM). Cells underwent two divisions within 10 days in cultures maintained in MX-82 medium without a medium change, and cells grew to increased final cell densities when the medium was renewed every third day. When the medium MX-82 was enriched by the addition of lipids, intermediary metabolites, and trace metals (medium MX-83), cells grew to higher densities. In the absence of the growth factors, cells became quiescent and subsequently could be induced to synthesize DNA in response to EGF. With the increasing numbers of cells per dish, the growth response of the hepatocytes diminished. Levels of hepatocyte-specific albumin and alpha-fetoprotein mRNAs at day 0 were similar to those observed at day 10 in primary fetal rat hepatocyte cultures and were maintained at higher levels in medium MX-83 than in medium MX-82.

Animals↗

PubMed1989

Time-dependent effects of aldosterone on sodium transport and cell membrane resistances in rabbit distal colon.

Aldosterone stimulates Na+-absorption in rabbit distal colon. Due to circadian variations in plasma aldosterone level, Na+-transport varies in this epithelium. In vitro measurements (Ussing-chambers) yielded a trans-epithelial voltage (Vt) of 13 +/- 1.6 mV for low-transporting epithelia (LT) and 25.7 +/- 2 mV for high-transporting epithelia (HT). However, the comparison of transepithelial conductance (Gt) in LT epithelia (2.73 +/- 0.21 mS/cm2) and HT epithelia (2.96 +/- 0.41 mS/cm2) revealed no difference. Colons from both groups were stimulated by exogenous aldosterone (4 h prior to experiment). The transepithelial values changed as follows: LT epithelia showed a significantly increased Vt (26.1 +/- 4 mV) and Gt (3.74 +/- 0.23 mS/cm2), whereas in HT epithelia both parameters remained unchanged. Transepithelial amiloride-sensitive conductance was higher in HT than in LT. However, only in LT epithelia aldosterone increased this conductance. To get a more detailed view of the action of aldosterone, we used intracellular microelectrodes to calculate the resistances of apical (Ra), basolateral (Rbl) and paracellular (Rp) pathway. The calculation of the resistances was based on a lumped equivalent circuit model and changes in Ra were induced by 50 microM/l mucosal amiloride. Comparison of the control tissues revealed a lower Rbl only in HT tissues. In both groups stimulation by exogenous aldosterone led to a marked decrease of Ra. Furthermore Rbl was reduced to the same value as in HT control tissues. A leak resistance (Rl) was found, which was modulated by aldosterone in LT- and in HT epithelia. Differences in amiloride-sensitive transepithelial conductance between both epithelia groups could be explained by a regulation of Rl.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone↗

PubMed1989

Ion transport and electrophysiology in rabbit cecum.

We investigated the basic bioelectrical properties and the transport of Na+, Rb+, and Cl- in the isolated cecal epithelium of the rabbit. Intracellular microelectrode recordings provided first estimates of the individual membrane potentials and resistances. The cecal epithelium was found to be a moderately tight epithelium with a high transepithelial potential and a relative high paracellular resistance. It has, however, a low transepithelial resistance caused by a high rate of transcellular ion transport and a high transcellular conductance. Under short-circuit conditions Na+ and Cl- are absorbed, whereas Rb+ is secreted. Na+ absorption seems to be mediated via an electrogenic mechanism with low amiloride sensitivity and is partially linked to Cl- transport. Cl- absorption is not influenced by secretagogues, and Rb+ secretion occurs via a transcellular route. A basolateral K+ conductance was also found. The results show rabbit cecum as an epithelium with a high electrolyte transport capacity, distinctly different from the neighboring proximal colon, and suited to absorb the large quantities of electrolytes that are present in the luminal liquid.

Animals↗

PubMed1989

[Escape of hydrogen peroxide and oxygen from the root canal].

In vitro investigations demonstrate that hydrogen peroxide, like the oxygen emitted from the root canal, escapes into the area around the root. The amount measurable was dependent on the concentration, the amount of time that the hydrogen peroxide was left in the root canal and the patency of the foramen apicale. The growth of the Staphylococcus aureus (SG 511) was restricted in the area around those roots whose root canal contained a 5% solution of hydrogen peroxide.

Dental Pulp Cavity↗

PubMed1988

[Therapy of aneurysm-induced subarachnoid hemorrhage].

Based on our experience with 115 consecutive patients treated in our department for aneurysmal subarachnoid haemorrhage between August 1984 and January 1988, problems of patient selection for early and late surgery as well as medical therapy are discussed. Overall surgical mortality was 6.7%. Surgical mortality was 12.1% for patients operated within 72 hours post SAB, whereas it was 4.2% for patients treated at later intervals. The value of transcranial Doppler sonography for timing of aneurysm surgery is stressed.

Follow-Up Studies↗

PubMed1988

Influence of dextran on the absorption of adrenaline-containing lignocaine solutions: a protective mechanism in local anaesthesia.

The effect of adding 6% dextran to a lignocaine solution containing adrenaline was studied in 27 neurosurgical patients during modified neuroleptanaesthesia. Before trepanation they received infiltration anaesthesia of the scalp at the site of the proposed operation. For a period of 1 h following injection plasma concentrations of adrenaline were measured by high pressure liquid chromatography and serum concentrations of lignocaine by gas chromatography. The addition of dextran caused a significant reduction in the absorption of both adrenaline and lignocaine from the injection site. It is concluded that the dextran adjuvant constitutes a protective mechanism against toxic systemic side effects in local anaesthesia using adrenaline-containing anaesthetic solutions. This effect is particularly significant in patients with pre-existing cardiovascular disease and when local anaesthetic solutions are used in combination with volatile anaesthetics.

Absorption↗

PubMed1988

Immortalization and malignant transformation of hepatocytes by transforming genes of polyoma virus and of SV40 virus in vitro and in vivo.

Hepatocytes can be converted into permanently growing hepatocyte lines by the transforming genes of either polyoma virus or SV40 virus. In transgenic mice harboring SV40 virus sequences (strain 202) most of the hepatocytes in the liver during late fetal development display an immortalized phenotype in culture, which is apparent immediately after placing liver cells into primary cultures. We conclude that at the late fetal stage hepatocytes in the liver display similar properties which might be the "initiated" cell type discussed earlier, and while untransformed, is determined to become malignant at a later point in development. Immortalized hepatocyte lines derived from the transgenic animals display reduced growth factor requirements in culture, i.e., increased autonomy. With time in culture, cells become increasingly autonomous by further reduction of their growth requirements until the final autonomous state has been attained, i.e., growth in the absence of any growth factor or hormone. It remains to be seen whether the development towards HCC in the normal liver is accompanied by a similar increased autonomy of growth factors, as observed in cells in culture.

Animals↗

PubMed1988

Impairment of the respiratory chain in the b-c1 region as early functional event during Fe2+/ascorbate induced peroxidation in rat liver mitochondria.

An attack at the level of the respiratory chain was established as the reason for the early inhibition of oxygen uptake during Fe2+/ascorbate induced peroxidation by following the activities of complexes I-IV separately. The close correlation between the decline of mitochondrial respiration and the activity of complex III strongly suggests that an impairment of the respiratory chain in the b-c1 region represents one of the first functional events in the causal sequence of peroxidative reactions preceding the phase of massive malondialdehyde production.

Animals↗

PubMed1988

[General and special problems concerning the approval and re-evaluation of antimicrobial agents for use in agriculturally useful animals].

Problems associated with registration and reevaluation of drugs are discussed in this paper. In particular it deals with difficulties resulting from toleration of residue concentrations in edible tissues and from the deduction of withdrawal periods. Possible consequences when applying identical criteria for registration and reevaluation are outlined. The necessity to involve the whole veterinary profession, when setting criteria for determination, presentation and evaluation of clinical efficacy, is stressed.

Animals↗