Biomedical subjects

A Tholen

Publications and source records attributed to A Tholen.

6 recordsLinked to original sources

PubMed2000

Characterization of abundance and diversity of lactic acid bacteria in the hindgut of wood- and soil-feeding termites by molecular and culture-dependent techniques.

Lactic acid bacteria have been identified as typical and numerically significant members of the gut microbiota of Reticulitermes flavipes and other wood-feeding lower termites. We found that also in the guts of the higher termites Nasutitermes arborum (wood-feeding), Thoracotermes macrothorax, and Anoplotermes pacificus (both soil-feeding), lactic acid bacteria represent the largest group of culturable carbohydrate-utilizing bacteria (3.6-5.2x10(4) bacteria per gut; 43%-54% of all colonies). All isolates were coccoid and phenotypically difficult to distinguish, but their enterobacterial repetitive intergenic consensus sequence (ERIC) fingerprint patterns showed a significant genetic diversity. Six different genotypes each were identified among the isolates from R. flavipes and T. macrothorax, and representative strains were selected for further characterization. By 16S rRNA gene sequence analysis, strain RfL6 from R. flavipes was classified as a close relative of Enterococcus faecalis, whereas strain RfLs4 from R. flavipes and strain TmLO5 from T. macrothorax were closely related to Lactococcus lactis. All strains consumed oxygen during growth on glucose and cellobiose; oxygen consumption of these and other isolates from both termite species was due to NADH and pyruvate oxidase activities, but did not result in H2O2 formation. In order to assess the significance of the isolates in the hindgut, denaturing gradient gel electrophoresis was used to compare the fingerprints of 16S rRNA genes in the bacterial community of R. flavipes with those of representative isolates. The major DNA band from the hindgut bacterial community was further separated by bisbenzimide-polyethylene glycol electrophoresis, and the two resulting bands were sequenced. Whereas one sequence belonged to a spirochete, the second sequence was closely related to the sequences of the Lactococcus strains RfLs4 and TmLO5. Apparently, those isolates represent strains of a new Lactococcus species which forms a significant fraction of the complex hindgut community of the lower termite R. flavipes and possibly also of other termites.

Animals↗

PubMed2000

Impact of oxygen on metabolic fluxes and in situ rates of reductive acetogenesis in the hindgut of the wood-feeding termite Reticulitermes flavipes.

The symbiotic digestion of lignocellulose in the hindgut of the wood-feeding termite Reticulitermes flavipes is characterized by two major metabolic pathways: (i) the oxidation of polysaccharides to acetate by anaerobic hydrogen-producing protozoa; and (ii) the reduction of CO2 by hydrogenotrophic acetogenic bacteria. Both reactions together would render the hindgut largely homoacetogenic. However, the results of this study show that the situation is more complex. By microinjection of radiolabelled metabolites into intact agarose-embedded hindguts, we showed that the in situ rates of reductive acetogenesis (3.3 nmol termite(-1) h(-1)) represent only 10% of the total carbon flux in the living termite, whereas 30% of the carbon flux proceeds via lactate. The rapid turnover of the lactate pool (7.2 nmol termite(-1) h(-1)) consolidates the previously reported presence of lactic acid bacteria in the R. flavipes hindgut and the low lactate concentrations in the hindgut fluid. However, the immediate precursor of lactate remains unknown; the low turnover rates of injected glucose (< 0.5 nmol termite(-1) h(-1)) indicate that free glucose is not an important intermediate under in situ conditions. The influence of the incubation atmosphere on the turnover rate and the product pattern of glucose and lactate confirmed that the influx of oxygen via the gut epithelium and its reduction in the hindgut periphery have a significant impact on carbon and electron flow within the hindgut microbial community. The in situ rates of reductive acetogenesis were not significantly affected by the presence of oxygen or exogenous H2, which is in agreement with a localization of homoacetogens in the anoxic gut lumen rather than in the oxic periphery. This adds strong support to the hypothesis that the co-existence of methanogens and homoacetogens in this termite is based on the spatial arrangement of the different populations of the gut microbiota. A refined model of metabolic fluxes in the hindgut of R. flavipes is presented.

Acetates↗

PubMed1999

An intelligent system for pacemaker reprogramming.

The process of reprogramming a cardiac pacemaker can be described in terms similar to those used for describing diagnostic problem solving. In this paper, the process of reprogramming a pacemaker is formalized as a special form of abductive diagnostic reasoning, where observable findings are interpreted with respect to results obtained from diagnostic tests. The dynamics of this process is cast as a diagnostic strategy, where information is gathered in a structured fashion. This abductive theory of pacemaker reprogramming has been used as the basis for an actual system that in its present form is capable of assisting cardiologists in dealing with problems in atrial sensing and pacing. The performance of the system has been evaluated using data from actual patients.

Algorithms↗

PubMed1999

Localization and in situ activities of homoacetogenic bacteria in the highly compartmentalized hindgut of soil-feeding higher termites (Cubitermes spp.).

Methanogenesis and homoacetogenesis occur simultaneously in the hindguts of almost all termites, but the reasons for the apparent predominance of methanogenesis over homoacetogenesis in the hindgut of the humivorous species is not known. We found that in gut homogenates of soil-feeding Cubitermes spp., methanogens outcompete homoacetogens for endogenous reductant. The rates of methanogenesis were always significantly higher than those of reductive acetogenesis, whereas the stimulation of acetogenesis by the addition of exogenous H(2) or formate was more pronounced than that of methanogenesis. In a companion paper, we reported that the anterior gut regions of Cubitermes spp. accumulated hydrogen to high partial pressures, whereas H(2) was always below the detection limit (<100 Pa) in the posterior hindgut, and that all hindgut compartments turned into efficient H(2) sinks when external H(2) was provided (D. Schmitt-Wagner and A. Brune, Appl. Environ. Microbiol. 65:4490-4496, 1999). Using a microinjection technique, we found that only the posterior gut sections P3/4a and P4b, which harbored methanogenic activities, formed labeled acetate from H(14)CO(3)(-). Enumeration of methanogenic and homoacetogenic populations in the different gut sections confirmed the coexistence of both metabolic groups in the same compartments. However, the in situ rates of acetogenesis were strongly hydrogen limited; in the P4b section, no activity was detected unless external H(2) was added. Endogenous rates of reductive acetogenesis in isolated guts were about 10-fold lower than the in vivo rates of methanogenesis, but were almost equal when exogenous H(2) was supplied. We conclude that the homoacetogenic populations in the posterior hindgut are supported by either substrates other than H(2) or by a cross-epithelial H(2) transfer from the anterior gut regions, which may create microniches favorable for H(2)-dependent acetogenesis.

Animals↗

PubMed1985

[Cardiocirculatory effects of a new sympathomimetic, amezinium methyl sulfate. Results of human pharmacological studies].

Changes in haemodynamic, inotropic state, and myocardial oxygen consumption were investigated in a total of eight patients with coronary artery disease after intravenous injection of 0.07 mg/kg amezinium methyl sulfate (LU 1631, Supratonin). It was demonstrated, that the principal effects of amezinium are consistent with those of a sympathomimetic agent which stimulates vascular alpha- and beta 1-adrenoreceptors. Amezinium (0.07 mg/kg) increased cardiac index, mean arterial pressure and total systemic resistance and dp/dtmax, while there were only minor changes in stroke index, mean pulmonary pressure and total pulmonary vascular resistance. In accordance with the changes in haemodynamics there was a 21.5% increase in myocardial oxygen consumption. But there were no signs of imbalance between oxygen supply and oxygen demand.

Adult↗

PubMed1984

[Therapeutic use of amezinium methylsulfate--a new, long acting, sympathomimetic--in paraspinal conduction anesthesia].

Cardiovascular effects of the new sympathomimetic ameziniummetilsulphate were investigated in 25 patients compared with a control group (n = 25). During spinal/epidural anaesthesia 5 mg amezinium was given i.v. if blood pressure dropped greater than 20 mmHg. from starting-point. A significant recovery of blood pressure (epidural anaesthesia: syst 21%, diast 9%; spinal anaesthesia: syst 13%, diast 6.6%) and a decrease in heart rate (6.8% resp. 4,5%) were thought due to peripheral vasoconstriction. Amezinium proved a stimulating drug for alpha- and beta 1-receptors by stabilising the systemic blood pressure in spinal/epidural anaesthesia.

Anesthesia, Epidural↗