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Biomedical subjects

D M Ward

Publications and source records attributed to D M Ward.

At least 91 records · Page 5Linked to original sources
PubMed1988

Photoexcretion and fate of glycolate in a hot spring cyanobacterial mat.

Photosynthesis by Synechococcus lividus, the sole oxygenic phototroph inhabiting the surface of the 55 degrees C cyanobacterial mat in Mushroom Spring, Yellowstone National Park, causes superoxic and alkaline conditions which promote glycolate photoexcretion. At O(2) concentrations characteristic of the top 2 mm of mat during the day, up to 11.8% of NaHCO(3) fixed in the light was excreted, and glycolate accounted for up to 58% of the excreted photosynthate. Glycolate was neither incorporated nor metabolized by S. lividus, but it was incorporated by filamentous microorganisms in the mat. Incubation of mat samples with NaHCO(3) resulted in labeling of both S. lividus and filaments, but the addition of nonradioactive glycolate increased the level of C in the aqueous phase and decreased the extent of labeling of filaments. This suggests that cross-feeding of glycolate from S. lividus to filamentous heterotrophs occurs and that underestimation of the extent of photoexcretion is probable.

Journal Article↗
PubMed1987

Kidney transplantation in the cyclosporine era.

Seventy-seven patients underwent transplantation, using a cyclosporine-prednisone immunosuppression protocol. No recipients died, and graft survival at one year was 100% for living related donor (LRD) recipients and 84% for cadaver donor (CD) recipients. Nineteen percent of locally harvested, flush-cooled kidney recipients required dialysis, whereas imported kidneys had a 66% dialysis rate. Infectious complications occurred in 17% of patients. Mean hospitalization was 12.8 days for LRD recipients and 13.6 days for CD recipients. Twenty-eight patients required 37 readmissions, mostly for treatment of rejection and infections. Total two-year cost for LRD transplants was +21,400; for CD transplants, +23,900.

Cyclosporins↗
PubMed1987

Measurement and interpretation of maximal oxygen uptake in patients with chronic cardiac or circulatory failure.

Rapidly responding gas analyzers have simplified the monitoring of oxygen uptake (VO2) in the clinical exercise laboratory. An incremental, exhaustive, upright exercise test can be safely used to determine the plateau in oxygen uptake during exercise, or maximal VO2 (VO2max), in patients with chronic cardiac or circulatory failure. We define VO2max in these patients as an increase in VO2 of less than 1 ml/min/kg despite an increment in work load. The value for VO2max indicates the patient's aerobic capacity; it also predicts the maximal cardiac output during exercise and therefore serves as an estimate of cardiac reserve and of the severity of cardiac or circulatory failure. Symptom-limited VO2 during exercise, termed maximum oxygen uptake but more appropriately peak VO2, bears no relationship to VO2max. The two terms should not be used interchangeably.

Cardiac Output↗
PubMed1987

Formation and fate of fermentation products in hot spring cyanobacterial mats.

The fate of representative fermentation products (acetate, propionate, butyrate, lactate, and ethanol) in hot spring cyanobacterial mats was investigated. The major fate during incubations in the light was photoassimilation by filamentous bacteria resembling Chloroflexus aurantiacus. Some metabolism of all compounds occurred under dark aerobic conditions. Under dark anaerobic conditions, only lactate was oxidized extensively to carbon dioxide. Extended preincubation under dark anaerobic conditions did not enhance anaerobic catabolism of acetate, propionate, or ethanol. Acetogenesis of butyrate was suggested by the hydrogen sensitivity of butyrate conversion to acetate and by the enrichment of butyrate-degrading acetogenic bacteria. Accumulation of fermentation products which were not catabolized under dark anaerobic conditions revealed their importance. Acetate and propionate were the major fermentation products which accumulated in samples collected at temperatures ranging from 50 to 70 degrees C. Other organic acids and alcohols accumulated to a much lesser extent. Fermentation occurred mainly in the top 4 mm of the mat. Exposure to light decreased the accumulation of acetate and presumably of other fermentation products. The importance of interspecies hydrogen transfer was investigated by comparing fermentation product accumulation at a 65 degrees C site, with naturally high hydrogen levels, and a 55 degrees C site, where active methanogenesis prevented significant hydrogen accumulation. There was a greater relative accumulation of reduced products, notably ethanol, in the 65 degrees C mat.

Journal Article↗
PubMed1987

Use of chloroflexus-specific antiserum to evaluate filamentous bacteria of a hot spring microbial mat.

Polyclonal antiserum prepared against Chloroflexus aurantiacus reacted with all Chloroflexus strains examined but not with other morphologically or physiologically similar bacteria. Only one of three filament types in a natural hot spring cyanobacterial mat reacted with this antiserum. Reacting filaments remained antigenically positive deep within the mat in material estimated to be several years old.

Journal Article↗
PubMed1986

Mitogenic agents induce redistribution of transferrin receptors from internal pools to the cell surface.

Incubation of serum-growth HeLa cells in serum-free medium causes a rapid (t1/2 3 min) 30-60% decrease in the binding of 125I-diferric transferrin to the cell surface. Addition of fetal bovine serum to cells in serum-free medium results in a rapid (t1/2 3 min) and concentration-dependent increase in binding activity. The loss or gain in ligand binding is a result of changes in surface receptor number rather than an alteration in ligand-receptor affinity. A variety of hormones (insulin, insulin-like growth factor, interleukin 1 and platelet-derived factor) were found to mimic the effect of serum on receptor number. The alteration in surface receptor number was found to be calcium-dependent. Changes in surface receptor number were independent of either receptor biosynthetic rate or the absolute cellular content of receptors. The effect of insulin or serum on Hela cell transferrin receptor distribution was unaffected by the presence of transferrin, demonstrating that receptor distribution in this cell type is ligand-independent. The ability of serum or insulin to modify surface transferrin receptor number was also observed in mouse L-cells, human skin fibroblasts, and J774 macrophage tumour cells. However, transferrin receptors on K562 and Epstein-Barr virus-transformed human lymphoblasts were unaltered by these agents. The quantities of receptors whose distribution is predominantly on the surface (i.e. epidermal growth factor or low density lipoprotein receptor) were unaltered by addition of the mitogenic agents. These results extend our previous studies [H.S. Wiley & J. Kaplan (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 7456-7460] demonstrating that mitogenic agents can induce redistribution of receptor pools in selected cell types.

Blood↗
PubMed1986

Nonenzymatically glucosylated serum proteins in patients with end-stage renal disease.

We report here abnormally elevated levels of nonenzymatically glucosylated whole-serum proteins in nondiabetic, as well as diabetic patients with end-stage renal disease (ESRD). Increased glucosylation of serum proteins and structural proteins has been documented in patients with diabetes mellitus, but not previously in ESRD. Increased levels of hemoglobin A1 have been reported in patients with ESRD, but appear to be due to carbamylation of hemoglobin rather than glucosylation. Using an assay that does not detect carbamylation, the present study demonstrates abnormally elevated levels of nonenzymatically glucosylated whole-serum proteins in all the chronic hemodialysis and continuous ambulatory peritoneal dialysis (CAPD) patients studied. Further, we found no change in levels of these abnormal proteins when patients were changed from hemodialysis with a dialysate that contained no glucose to one that did, or to CAPD in which large amounts of glucose are absorbed from the dialysate. The mode of dialysis does not appear to affect glucosylated protein levels in ESRD.

Adult↗
PubMed1986

Direct antigen binding to glomerular immune complex deposits.

We evaluated the contribution of intrarenal factors in the increased renal accumulation of bovine serum albumin (BSA) in chronic serum sickness (CSS). Renal transplantation was used to study 125I BSA uptake (single and paired label techniques) in normal and CSS kidneys exposed to the same immunologic milieu. In CSS, the daily dose of BSA (dose 15 to 150 mg) was substituted with radiolabeled BSA. Uptake in washed kidney homogenates (24 hours) in the recipient's native CSS kidney varied from 0.29 to 38.40 micrograms/g of kidney (mean 11.70) compared to 0.09 to 2.19 micrograms/g (mean 1.01) in the transplanted normal kidney. The ratio of uptake in the CSS/normal kidney varied from 2.1 to 17.5. These findings indicated that intrarenal factors were important in renal uptake since both kidneys had been exposed to the same circulating immune complex load. Transplantation between "early" (nonproteinuric) and late (proteinuric) CSS rabbits again suggested intrarenal factors influence the uptake of 125I BSA immune complex components with late CSS kidney/early CSS kidney uptake ratios of 25 and 49 in the pairs examined. When CSS kidneys were transplanted into normal rabbits, the binding of 1 to 160 mg of radiolabeled BSA in the transplanted CSS kidney varied from 0.68 to 22.89 micrograms/g (mean 7.15) compared to 0.01 to 0.84 microgram/g (mean 0.18) in the normal rabbit's native kidney. The uptake in the CSS kidney always exceeded that in the recipient's normal kidney (ratio varied from 18 to 289). The binding of radiolabeled BSA in the CSS kidney was quantitatively similar to that found previously in the intact CSS rabbit.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Phenylarsine oxide-induced increase in alveolar macrophage surface receptors: evidence for fusion of internal receptor pools with the cell surface.

Rabbit alveolar macrophages which were treated at 0 degrees C with phenylarsine oxide and then incubated at 37 degrees C for 10 min exhibited a two- to threefold increase in surface receptor activity for macroglobulin.protease complexes, diferric transferrin, and mannose-terminal glycoproteins. Analysis of the concentration-dependence of ligand binding indicated that changes in ligand-binding activity were due to changes in receptor number rather than alterations in ligand-receptor affinity. Surface receptor number could also be increased by treatment of cells with three other sulfhydryl reagents, N-ethylmaleimide, p-chloromercurobenzoate, and iodoacetic acid. The increase in receptor activity was maximal after 10 min and decreased over the next hour. This decrease in cell-associated receptor activity was due to the release of large membrane vesicles which demonstrated a uniform buoyant density by isopycnic sucrose gradient centrifugation. Treatment of cells with phenylarsine oxide did not decrease the cellular content of lactate dehydrogenase or beta-galactosidase, indicating that cell integrity was maintained and lysosomal enzyme release did not occur. Our studies indicate that phenylarsine oxide treatment in the presence of extracellular Ca2+ results in the fusion of receptor-containing vesicles with the cell surface.

Animals↗
PubMed1984

Microelectrode studies of interstitial water chemistry and photosynthetic activity in a hot spring microbial mat.

Microelectrodes were used to measure oxygen, pH, and oxygenic photosynthetic activity in a hot spring microbial mat (Octopus Spring, Yellowstone National Park), where the cyanobacterium Synechococcus lividus and the filamentous bacterium Chloroflexus aurantiacus are the only known phototrophs. The data showed very high biological activities in the topmost layers of the microbial mat, resulting in extreme values for oxygen and pH. At a 1-mm depth at a 55 degrees C site, oxygen and pH reached 900 muM and 9.4, respectively, just after solar noon, whereas anoxic conditions with a pH of 7.2 were measured before sunrise. Although diurnal changes between these extremes occurred over hours during a diurnal cycle, microbial activity was great enough to give the same response in 1 to 2 min after artificial shading. Oxygenic photosynthesis was confined to a 0.5- to 1.1-mm layer at sites with temperatures at or above about 50 degrees C, with maximum activities in the 55 to 60 degrees C region. The data suggest that S. lividus is the dominant primary producer of the mat.

Journal Article↗
PubMed1984

Use of beta-blockade and hemoperfusion for acute theophylline poisoning.

Five adults were treated successfully for severe theophylline poisoning due to intentional overdosage. Clinical features included nausea, tremor, delirium, hypotension and cardiac arrhythmias, metabolic acidosis, hyperglycemia, hypokalemia and hypophosphatemia. No seizures or deaths occurred despite very high serum theophylline concentrations (between 96 and 194 mug per ml). Extreme elevations of plasma catecholamines were documented and are implicated in the toxicity. beta-Blockade with intravenous administration of propranolol hydrochloride was the most effective therapy for theophylline-induced hypotension. All patients were treated with resin hemoperfusion, which resulted in significant clinical improvement and rapid lowering of the serum theophylline level.

Adolescent↗
PubMed1983

Anaphylatoxin formation during hemodialysis: comparison of new and re-used dialyzers.

Hemodialysis of 11 endstage renal failure patients with new cuprophan hollow fiber dialyzers produced significant leukopenia as well as increased plasma levels of both C3a and C5a antigens during the initial phases of the procedure. Formalin-fixed new dialyzers produced quantitatively similar phenomena in eight of these same patients. By contrast, hemodialysis with re-used dialyzers, that is dialyzers exposed to blood prior to formalin sterilization, produced only a 20 to 30% decline in peripheral blood leukocyte counts. Correspondingly, C3a antigen formation within re-used dialyzers was only 20% of that observed in new dialyzers. Re-used dialyzers also differed significantly from either new or formalin-fixed new dialyzers in that C3b antigen could be readily detected within them even after extensive washing. These observations suggest that C3b deposition on the cellulosic membrane surface during first use markedly diminishes the complement activating potential of cuprophan dialyzers when they are subsequently re-used.

Adult↗
PubMed1983

Substrates for sulfate reduction and methane production in intertidal sediments.

The activity of and potential substrates for methane-producing bacteria and sulfate-reducing bacteria were examined in marsh, estuary, and beach intertidal sediments. Slow rates of methane production were detected in all sediments, although rates of sulfate reduction were 100- to 1,000-fold higher. After sulfate was depleted in sediments, the rates of methane production sharply increased. The addition of methylamine stimulated methanogenesis in the presence of sulfate, and [C]methylamine was rapidly converted to CH(4) and CO(2) in freshly collected marsh sediment. Acetate, hydrogen, or methionine additions did not stimulate methanogenesis. [methyl-C]methionine and [2-C]acetate were converted to CO(2) and not to CH(4) in fresh sediment. No reduction of CO(2) to CH(4) occurred in fresh sediment. Molybdate, an inhibitor of sulfate reduction, inhibited [2-C]acetate metabolism by 98.5%. Fluoracetate, an inhibitor of acetate metabolism, inhibited sulfate reduction by 61%. These results suggest that acetate is a major electron donor for sulfate reduction in marine sediments. In the presence of high concentrations of sulfate, methane may be derived from novel substrates such as methylamine.

Journal Article↗
PubMed1983

Oxygen Microelectrode That Is Insensitive to Medium Chemical Composition: Use in an Acid Microbial Mat Dominated by Cyanidium caldarium.

A novel oxygen microelectrode with a tip diameter of 2 to 20 mum was constructed which could function satisfactorily under a variety of environmental conditions and in a variety of media, including human blood serum, citric acid at pH 2.5, moist air, and paraffin oil. Measurement of oxygen by this electrode does not require stirring of the medium. Electrodes could be made so that the 90% response time necessary to detect changes in oxygen concentration was less than 0.2 s, and response was linear with oxygen concentration. To demonstrate the performance of the electrode, oxygen and photosynthesis profiles of an acid microbial mat (pH 2.8) dominated by the eucaryotic alga Cyanidium caldarium were made. Photosynthetic rates as high as 95 mmol of O(2) dm h were measured within the most active 0.1-mm layer, which was ca. 0.2 mm below the surface of the microbial mat. The total photosynthetic activity was 47 mmol of O(2) m h. Vertical profiles of photosynthesis at different light intensities showed that the microalgae within the mat were not photoinhibited at bright sunlight (2,090 muEinsteins m s).

Journal Article↗
PubMed1982

Temperature adaptations in the terminal processes of anaerobic decomposition of yellowstone national park and icelandic hot spring microbial mats.

The optimum temperatures for methanogenesis in microbial mats of four neutral to alkaline, low-sulfate hot springs in Yellowstone National Park were between 50 and 60 degrees C, which was 13 to 23 degrees C lower than the upper temperature for mat development. Significant methanogenesis at 65 degrees C was only observed in one of the springs. Methane production in samples collected at a 51 or 62 degrees C site in Octopus Spring was increased by incubation at higher temperatures and was maximal at 70 degrees C. Strains of Methanobacterium thermoautotrophicum were isolated from 50, 55, 60, and 65 degrees C sites in Octopus Spring at the temperatures of the collection sites. The optimum temperature for growth and methanogenesis of each isolate was 65 degrees C. Similar results were found for the potential rate of sulfate reduction in an Icelandic hot spring microbial mat in which sulfate reduction dominated methane production as a terminal process in anaerobic decomposition. The potential rate of sulfate reduction along the thermal gradient of the mat was greatest at 50 degrees C, but incubation at 60 degrees C of the samples obtained at 50 degrees C increased the rate. Adaptation to different mat temperatures, common among various microorganisms and processes in the mats, did not appear to occur in the processes and microorganisms which terminate the anaerobic food chain. Other factors must explain why the maximal rates of these processes are restricted to moderate temperatures of the mat ecosystem.

Journal Article↗
PubMed1981

Fate of immediate methane precursors in low-sulfate, hot-spring algal-bacterial mats.

The fates of acetate and carbon dioxide were examined in several experiments designed to indicate their relative contributions to methane production at various temperatures in two low-sulfate, hot-spring algal-bacterial mats. [2-C]acetate was predominantly incorporated into cell material, although some CH(4) and CO(2) was produced. Acetate incorporation was reduced by dark incubation in short-term experiments and severely depressed by a 2-day preincubation in darkness. Autoradiograms showed that acetate was incorporated by long filaments resembling phototrophic microorganisms of the mat communities. [H]acetate was not converted to CH(4) in samples from Octopus Spring collected at the optimum temperature for methanogenesis. NaHCO(3) was readily converted to CH(4) at temperatures at which methanogenesis was active in both mats. Comparisons of the specific activities of methane and carbon dioxide suggested that of the methane produced, 80 +/- 6% in Octopus Spring and 71 +/- 21% in Wiegert Channel were derived from carbon dioxide. Addition of acetate to 1 mM did not reduce the relative importance of carbon dioxide as a methane precursor in samples from Octopus Spring. Experiments with pure cultures of Methanobacterium thermoautotrophicum suggested that the measured ratio of specific activities might underestimate the true contribution of carbon dioxide in methanogenesis.

Journal Article↗