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Biomedical subjects

A Jahn

Publications and source records attributed to A Jahn.

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

[Quality of prenatal data in the Hessian Perinatal Registry. A comparison with data from maternal health record and results of a pregnancy survey].

In the Federal State of Hesse, Germany, pregnancy and delivery related data are collected in a central perinatal registry called "Hessische Perinatalerhebung" (HEPE) since 1981, the objective being to enforce quality assurance and to contribute to a reduction in perinatal mortality and morbidity. The delivery unit compiles these data based on the antenatal record called "Mother Passport" and the actual delivery. In order to check on the quality of data, information on risk factors obtained from the perinatal register was compared to information from antenatal records and from a questionnaire administered to pregnant women prior to delivery. The study population comprised 1978 women who delivered at the maternity unit of the Municipal Hospital of Wiesbaden, the Dr. Horst Schmidt Kliniken, in 1990 and 1991. Comparison of the three data sources revealed substantial differences: Almost all risk factors were most frequently mentioned by the mothers themselves, less by the antenatal record and even less by the perinatal register. These differences were less pronounced for data on previous pregnancies and pre-existing disease and on abnormal positioning. Considerable differences were found in relation to pregnancy induced hypertension, intra-uterine growth retardation, incapacity of the cervix, preterm labour and bleeding. Risk factors related to the social environment and personal habits like psycho-social stress and smoking were found to be extremely under-reported in the antenatal records as well as in the perinatal register. The following factors could be identified as major reasons for the different risk profiles obtained from the various data sources: [1] Data loss through the transfer of data from the antenatal record to the record form of the perinatal register or to the computer, [2] selective recording of those risk factors considered by doctors to be particularly relevant, [3] missing definition of some risk factors and [4] recording of antenatal data for the perinatal register by the delivery unit after knowing the pregnancy outcome. Antenatal data in the perinatal register of Hessen are doubtful and should not be used uncritically for comparative studies and the assessment of relative risks. The extreme under-reporting of some risk factors may even lead to giving some interventions undue priority. In future, regular validity studies should become routine. A reduction of the data losses as well as a clear separation of antenatal data and delivery data could be achieved if antenatal data would be transferred from the doctor providing antenatal care direct to the perinatal register.

Data Collection↗
PubMed1995

Toxicity and metabolism of ochratoxin A.

The frequent occurrence of ochratoxin A (OA) in food and feed commodities and the high incidence of human exposure, as confirmed by different surveillance studies initiated several investigations devoted to elucidating the molecular mechanisms underlying OA toxicity. Previous studies indicated that the primary effects of OA are the inhibition of tRNA synthetase, the inhibition of mitochondrial respiration, and a disturbance of intracellular calcium homeostasis inherent to lipid peroxidation processes. We here report the effect of OA on a number of toxicological endpoints including cytotoxicity in different cell lines and effects on macromolecular synthesis and cell proliferation in primary cultures of hepatocytes at concentrations corresponding to overall exposure levels. These studies provide evidence that prominent toxicological effects might be linked to biotransformation processes. Analysis of hepatic biotransformation resulted in the detection of a number of distinct stable OA-metabolites. As metabolic activation has also been identified as an essential step in OA mutagenicity, the biological relevance on this mechanistic data is discussed.

Animals↗
PubMed1994

Optimizing photoheterotrophic H2 production by Rhodobacter capsulatus upon interposon mutagenesis in the hupL gene.

In Rhodobacter capsulatus, the hupL gene encoding the large subunit of the uptake-hydrogenase (Hup) enzyme complex was mutated by insertion of an interposon. The mutant neither synthesized an active hydrogenase nor grew photoautotrophically. Under conditions of nitrogen (N) limitation, photoheterotrophic cultures of the wild type and the mutant evolved H2 by activity of the nitrogenase enzyme complex. When grown with glutamate as an N source and either D,L-malate or L-lactate as carbon sources, the efficiency of H2 production by the HupL mutant was higher than 90%, whereas wild-type cultures exhibited efficiencies of 54% (with D,L-malate) and 64% (with L-lactate), respectively. With NH4+ as the N source, efficiencies of H2 production were 70% (mutant) and 52% (wild type).

Biotechnology↗
PubMed1993

Identification of a new class of nitrogen fixation genes in Rhodobacter capsulatus: a putative membrane complex involved in electron transport to nitrogenase.

DNA sequence analysis of a 12236 bp fragment, which is located upstream of nifE in Rhodobacter capsulatus nif region A, revealed the presence of ten open reading frames. With the exception of fdxC and fdxN, which encode a plant-type and a bacterial-type ferredoxin, the deduced products of these coding regions exhibited no significant homology to known proteins. Analysis of defined insertion and deletion mutants demonstrated that six of these genes were required for nitrogen fixation. Therefore, we propose to call these genes rnfA, rnfB, rnfC, rnfD, rnfE and rnfF (for Rhodobacter nitrogen fixation). Secondary structure predictions suggested that the rnf genes encode four potential membrane proteins and two putative iron-sulphur proteins, which contain cysteine motifs (C-X2-C-X2-C-X3-C-P) typical for [4Fe--4S] proteins. Comparison of the in vivo and in vitro nitrogenase activities of fdxN and rnf mutants suggested that the products encoded by these genes are involved in electron transport to nitrogenase. In addition, these mutants were shown to contain significantly reduced amounts of nitrogenase. The hypothesis that this new class of nitrogen fixation genes encodes components of an electron transfer system to nitrogenase was corroborated by analysing the effect of metronidazole. Both the fdxN and rnf mutants had higher growth yields in the presence of metronidazole than the wild type, suggesting that these mutants contained lower amounts of reduced ferredoxins.

Amino Acid Sequence↗
PubMed1990

Control of diauxic growth of Azotobacter vinelandii on acetate and glucose.

Batch cultures of Azotobacter vinelandii were inoculated with cells pregrown on either acetate or glucose. When they were subsequently grown on a mixture of acetate and glucose, typical diauxic growth was observed, with preferential uptake of acetate in the first and glucose in the second phase of growth. Extracts from acetate-pregrown cells exhibited high acetate kinase activity in the first phase of growth. This activity decreased and activities of the two glucose enzymes glucose 6-phosphate dehydrogenase and glyceraldehyde 3-phosphate dehydrogenase increased in the second phase. Extracts from glucose-pregrown cells exhibited high initial activities of the two glucose enzymes, which decreased while acetate kinase activity increased in the first phase of growth. Again, in the second phase, activities of the two glucose enzymes increased and acetate kinase activity decreased. In any case, isocitrate dehydrogenase activity varied only slightly and unspecifically. The differences in enzyme activity and the constancy of isocitrate dehydrogenase were confirmed by experiments with either acetate- or glucose-limited chemostats. In chemostats in which both of the substrates were limiting, all of the enzymes displayed significant activities. Glucose 6-phosphate dehydrogenase activity was inhibited by acetyl coenzyme A and acetyl phosphate but not by acetate. It is proposed that diauxic growth is based on the control of enzymes involved in acetate or glucose dissimilation by which acetate or its metabolites control the expression and activity of glucose enzymes.

Acetate Kinase↗
PubMed1988

Isolation and characterization of a variant of human papillomavirus type 11 from a nasal inverting (Schneiderian) papilloma.

We have previously reported the presence of a variant of human papillomavirus (HPV) type 11 in a nasal inverting papilloma [Respler et al., 1987]. In the present study, we have cloned molecularly the DNA of this variant at its unique restriction enzyme Bam HI site into lambda BF101 phage. Restriction enzyme mapping and DNA sequencing revealed that the genome of this virus contained an extra 531 base pair (bp) which was the repeat of most of the noncoding region (ncr) of HPV 11. Insertion of transcriptional control elements, including the repeated sequence, in front of the chloramphenicol acetyltransferase (CAT) gene resulted in a 5- to 30-fold increase in expression in transfected cells, as compared to the constructs containing a single ncr of HPV 11. This increased expression was due to enhanced levels of CAT RNA the synthesis of which is initiated by the viral promoter element.

Acetyltransferases↗
PubMed1986

Seroepidemiological study on kala-azar in Baringo District, Kenya.

This paper reports on 164 cases of kala-azar observed in the Baringo District of Kenya between February 1981 and February 1983. All were confirmed serologically by enzyme-linked immunosorbent assay (ELISA) and all but 20 by parasitological examination as well. Following the standard treatment with a 30 day course of sodium stibogluconate (Pentostam) two non-responders and four relapses were observed. Children between 2 and 15 years old were found to be the most affected age group; male patients predominated slightly at 57%. All cases occurred in the semi-arid and arid parts of the district below 1500 m, where pastoralism predominates. Besides scattered cases, certain kala-azar foci could be identified. Two of these--Endao with 49 households, 228 inhabitants and 13 cases of kala-azar, and Koriema with 22 households, 93 inhabitants and 11 cases--were subject to a house to house survey. People were examined physically, their weight and height recorded and fingerprick blood collected on blotting paper for later serological testing. Each household was mapped and the relevant environmental factors recorded. A positive correlation could be demonstrated between kala-azar cases and the vicinity of their homesteads to seasonal rivers and also between kala-azar cases and people living in timber houses, rather than mud and wattle houses. Eroded termite hills were not found to be of epidemiological importance. No satisfying explanation could be found for the striking temporal and local clustering of cases. The homestead was identified as an important site of transmission with optimum conditions for transmission occurring during supper in the evening. Based on spleen rates, Endao was classified as hyperendemic for malaria and Koriema as mesoendemic. Diagnostic ELISA values above 0.2 were observed in all cases of active kala-azar. However, ELISA values above 0.04, taken as the borderline non-specific reaction, could be found in about half of the study areas population. Therefore we conclude that asymptomatic infection must be common. Observations demonstrated that spontaneous recovery may follow clinical illness and visceralization of the parasite. Comparison of parasitological and serological data suggest that this may be expected in more than 15% of cases.

Adolescent↗
PubMed1983

Evaluation of a visually read ELISA for serodiagnosis and sero-epidemiological studies of kala-azar in the Baringo District, Kenya.

ELISA for detecting leishmanial antibodies was established at Baringo District Hospital Kabarnet, Kenya, and successfully applied in clinical routine and sero-epidemiological surveys. To simplify the procedure and to make it more economical, ELISA was read as visual endpoint titre and blood was collected by the blotting paper method. 63 parasitologically confirmed kala-azar patients all showed a diagnostic IgG specific ELISA titre of 1:27,000 or more, which indicates a sensitivity of 100%. 11 of 14 persons found with this diagnostic titre during a house-to-house survey in a known focus of kala-azar could be confirmed parasitologically. Two more showed typical signs and symptoms of kala-azar and were successfully treated accordingly. Controls from unaffected areas were all negative. Low titres of 1:1000 and 1:3000 were observed in healthy individuals from foci of kala-azar, but could be easily distinguished from active cases. ELISA has been shown to be a convenient and reliable method for the serodiagnosis of East African kala-azar. The technique can be integrated into the routine work of a clinical laboratory at the level of a district hospital, without sophisticated equipment and with a minimum of funds. Blood of suspected kala-azar cases can be collected on blotting paper in dispensaries and health centres near known foci and sent to the laboratory.

Antibodies↗
PubMed1980

Contrast sensitivity in children and adults.

Contrast sensitivity functions to vertical sinusoidal gratings have been measured in 135 subjects ranging from 3 to 29 years of age. The reported contrast sensitivities for all spatial frequencies increased steadily with age, reaching adult levels during adolescence. The usefulness of these functions as a clinical test is discussed.

Adolescent↗
PubMed1975

Carrier-mediated transfer of D-glucose in brush border vesicles derived from rabbit renal tubules. Na+-dependent versus Na+-independent transfer.

A brush border preparation from rabbit renal tubules containing a high yield of vesicles has been used to study the transfer of D-glucose through the brush border membrane. In the presence of an Na+ gradient across the vesicular membrane, the vesicles could concentrate D-glucose to a factor of 1.5, whereas in the absence of an Na+ gradient, only equilibrium with the medium was achieved. Two types of transfer could be distinguished by their requirement of Na+, their sensitivity to phlorizin and their pH optimum. The Na+-independent transfer was about 100 times less sensitive to phlorizin than the Na+-dependent path and exhibited a pH optimum between 7 and 8, whereas the Na+-dependent transfer was highest at a pH between 8 and 9. The brush border preparation could be freed of most of the contaminating material derived from the basal and lateral tubular cell membrane by a discontinuous density gradient centrifugation. It still showed both forms of transfer to a similar extent, indicating that both are located in the brush border membrane. A study of the sensitivity of D-glucose transfer to phlorizin, in the presence and absence of Na+ at different temperature, suggests a single carrier species functioning in two interchangeable conformational states with different affinities for phlorizin rather than two transfer systems working independently.

Adenosine Triphosphatases↗