Biomedical subjects

D A Christensen

Publications and source records attributed to D A Christensen.

At least 37 records · Page 2Linked to original sources

PubMed1999

Evaluation of wheat-based thin stillage as a water source for growing and finishing beef cattle.

Two trials were conducted to evaluate the nutritional value of wheat-based thin stillage as a water source for cattle. In Trial 1, 20 large-framed steers were fed a basal diet based primarily on barley grain and barley silage, with ad libitum access to water or thin stillage at one of three DM concentrations (2, 4, and 6.7%) in a completely randomized design. The trial consisted of a 70-d growing period and a finishing phase. In Trial 2, total-tract nutrient digestibility coefficients of the basal diet and water treatments fed in the growing period were determined in a randomized complete block design using 12 medium-framed steers. The results showed that when only DMI from the basal diet was considered, there was a linear reduction (P<.01) in DMI and a linear improvement (P<.01) in the gain:feed ratio with no effect on daily gain as thin stillage DM concentration increased. No differences were detected in DMI or efficiency of gain when total DMI (basal diet and thin stillage) was considered. Carcass traits indicated a trend toward increased (P<.06) carcass fat with increasing thin stillage DM concentration. Results of Trial 2 indicated a linear improvement (P<.05) in apparent digestibility of DM, CP, NDF, and energy of the total diet (basal diet and thin stillage) as thin stillage DM concentration increased. We concluded that supplementing growing and finishing cattle with thin stillage reduced the amount of the basal diet required for gain and improved nutrient utilization.

Animals↗

PubMed1999

Feeding value of wheat-based thin stillage: in vitro protein degradability and effects on ruminal fermentation.

Two experiments were conducted to evaluate the nutritive value of wheat-based thin stillage as a fluid source for ruminants. In vitro CP degradability of thin stillage was estimated relative to canola meal and heated canola meal in a completely randomized design. Four ruminally cannulated steers were used in a double cross-over design to determine the effects of consuming thin stillage or water as drinking sources on ruminal fermentation traits. The in vitro CP degradability of thin stillage (55.4%) was lower (P<.05) than that of canola meal (59.4%) and higher than that of heated canola meal (31.6%). Ruminal pH for steers consuming thin stillage was higher (P<.05) at 1000 and 1100 and lower (P<.05) at 1900 and 2000 than that for steers consuming water. Total VFA followed a pattern that was the reverse of that reported for pH. Ruminal NH3 N levels were higher (P<.05) for steers fed thin stillage than for water-fed steers through most of the collection period. Ruminal fluid and particulate matter passage rates were not affected by treatment and averaged .165 and .06 /h, respectively. The amount of thin stillage and water that did not equilibrate with the ruminal fluid and, thus, was considered to bypass the rumen was estimated to be 51.9 and 59.2% of total fluid consumed, respectively. Feeding wheat-based thin stillage had no adverse effects on ruminal metabolism.

Animals↗

PubMed1997

Calculation of electric fields induced near metal implants by magnetic resonance imaging switched-gradient magnetic fields.

Electric (E) fields induced near metal implants by MRI switched-gradient magnetic fields are calculated by a new equivalent-circuit numerical technique. Induced E-field results are found for a metallic spinal-fusion implant consisting of two thin wires connected to the metallic case of a current generator as well as for its subsections: a bare U-shaped wire, an insulated U-shaped wire, a cut insulated wire, and a generator. The presence of the metallic implants perturbs the E field significantly. Near the ends of the bare U-shaped wire, the E field is 89.7 times larger than in the absence of the wire. The greatest E field concentration occurs near the ends of the cut insulated wire, where the E field is 196.7 times greater than in the absence of the wire. In all cases, the perturbation of the induced E field by the implanted wire is highly localized within a few diameters of the wire.

Bone Wires↗

PubMed1997

Effect of chelating agents on the excretion of copper, zinc and iron in the bile and urine of sheep.

The effect of tetrathiomolybdate (TM), disodium calcium ethylenediamine tetraacetate (EDTA), D-penicillamine (PEN), 2-3 dimercapto-1-propanol (BAL) and dimethyl dithiocarbamate (DDC) administration on biliary and urinary excretion of copper (Cu), zinc (Zn) and iron (Fe) was investigated in sheep on a low Cu diet (Group A) and a high Cu diet (Group B). Only biliary Cu excretion increased significantly (P<0.01) with TM treatment. Urinary Cu excretion increased (P<0.01) following PEN treatment. TM, EDTA, PEN, BAL and DDC adminstration increased Cu excretion via bile and urine by 254, 11, 266, 46 and 16%, respectively in Group A sheep, and by 354, 13, 196, 20 and (-) 31% in Group B sheep. Urinary Zn excretion increased (P<0.01) following EDTA and PEN treatments. Only urinary Fe excretion increased (P<0.01) with EDTA treatment. The results show that TM and PEN are the most efficient decoppering agents, but PEN unlike TM also removes Zn. The major routes of excretion of Cu chelates by TM and PEN are different. TM increases Cu excretion significantly (P<0.05 in Group A and P<0.01 in Group B) in bile with only a slight increase in urinary Cu whereas PEN increases Cu excretion significantly (P<0.01) in urine. Therefore from a therapeutic view, a combination therapy of TM and PEN would be useful to maximize Cu removal from the body.

Animals↗

PubMed1997

Use of real-time ultrasound to evaluate live animal carcass traits in young performance-tested beef bulls.

Young bulls were ultrasonically scanned to 1) study breed differences for 12th rib fat depth (USFAT) and longissimus muscle area (USREA), 2) evaluate the nature and predictability of USFAT and USREA development, and 3) determine the effect of age (YFAT and YREA, respectively) or weight (WREA) adjustments on USFAT and USREA. Angus (AA), Charolais (CH), Hereford (HH), Shorthorn (SS), and Simmental (SM) bulls (n = 886) were studied in 2 yr at two stations. Breed differences were observed for end of test USFAT (AA = SS > HH > CH = SM, P < .05) and USREA (CH = SM > SS = AA > HH, P < .05). Within-breed coefficients of variation were 29.8 to 48.4% for end of test USFAT and from 9.0 to 10.8% for end of test USREA. In most bulls, USFAT development was neither linear nor quadratic (P > .05), but USREA development was linear (P < .05). Prediction equations were characterized by low r2 and high residual standard deviation (RSD) values, although those for d-84 USREA had r2 values from .63 to .70 and RSD values from 4.09 to 5.80 cm2. High associations were obtained between end of test USFAT with YFAT (r = .83 to .91, P < .05) and USREA with YREA (r = .74 to .84, P < .05) but not for end of test USREA with WREA (r = .31 to .56, P < .05). These results indicate that end of test ultrasound measurements may be a useful addition to performance testing programs.

Adipose Tissue↗

PubMed1996

Femtomolar sensitivity using a channel-etched thin film waveguide fluoroimmunosensor.

A dual channel, evanescent fluoroimmunoassay format is used to detect femtomolar analyte concentrations (i.e. less than 1 part per trillion [w/w]) on an etched channel siliconoxynitride thin film integrated optical waveguide. Two assays are used to demonstrate the dose-response behaviour of the sensor: (1) a direct assay of a fluorescently-labeled protein ligand binding to an immobilized protein receptor, and (2) an indirect sandwich assay of a non-fluorescent protein ligand binding to an immobilized protein receptor, as detected by the binding of a fluorescently-labeled secondary receptor protein. A red-emitting cyanine dye (Cy-5), which minimized background fluorescence and scatter losses of the waveguide, was used in both assays. To our knowledge, this is the first report of femtomolar sensitivity in an immunosensing instrument.

Biosensing Techniques↗

PubMed1996

The effects of weak extremely low frequency magnetic fields on calcium/calmodulin interactions.

Mechanisms by which weak electromagnetic fields may affect biological systems are of current interest because of their potential health effects. Lednev has proposed an ion parametric resonance hypothesis (Lednev, 1991, Bioelectromagnetics, 12:71-75), which predicts that when the ac, frequency of a combined dc-ac magnetic field equals the cyclotron frequency of calcium, the affinity of calcium for calcium-binding proteins such as calmodulin will be markedly affected. The present study evaluated Lednev's theory using two independent systems, each sensitive to changes in the affinity of calcium for calmodulin. One of the systems used was the calcium/calmodulin-dependent activation of myosin light chain kinase, a system similar to that previously used by Lednev. The other system monitored optical changes in the binding of a fluorescent peptide to the calcium/calmodulin complex. Each system was exposed to a 20.9 microT static field superimposed on a 20.9 microT sinusoidal field over a narrow frequency range centered at 16 Hz, the cyclotron frequency of the unhydrated calcium ion. In contrast to Lednev's predictions, no significant effect of combined dc-ac magnetic fields on calcium/calmodulin interactions was indicated in either experimental system.

Animals↗

PubMed1995

Structure of the fibre-forming protein pilin at 2.6 A resolution.

The crystallographic structure of Neisseria gonorrhoeae pilin, which assembles into the multifunctional pilus adhesion and virulence factor, reveals an alpha-beta roll fold with a striking 85 A alpha-helical spine and an O-linked disaccharide. Key residues stabilize interactions that allow sequence hypervariability, responsible for pilin's celebrated antigenic variation, within disulphide region beta-strands and connections. Pilin surface shape, hydrophobicity and sequence variation constrain pilus assembly to the packing of flat subunit faces against alpha 1 helices. Helical fibre assembly is postulated to form a core of coiled alpha 1 helices banded by beta-sheet, leaving carbohydrate and hypervariable sequence regions exposed to solvent.

Amino Acid Sequence↗

PubMed1993

The effect of sulphate on thiamine-destroying activity in rumen content cultures in-vitro.

The effect of sulphur on thiamine-destroying activity was studied in native or thiamine-spiked rumen content cultures. The treatments consisted of water [control (Ctrl)], sodium chloride (NaCl) and sodium sulphate (Na2SO4). A net gain (relative to 0 h) of thiamine in native cultures was observed for at least 48 h at levels of S ranging from 0.25 to 8 mg S added per ml of the culture and also in the Ctrl and respective NaCl cultures. However, after 48 h of incubation thiamine concentration was lower (p < 0.05) in native cultures treated with Na2SO4 relative to Ctrl and NaCl treatments. There was a linear (p < 0.03) time trend indicating an effect of Na2SO4 over time on changes in thiamine concentration in native rumen cultures. In thiamine-spiked rumen content cultures, the cultures treated with Na2SO4 produced higher (p < 0.05) thiamine-destroying activity. There was no effect of cation (Na) on thiamine-destroying activity. Initial heat treatment of thiamine-spiked cultures inactivated part of the thiamine-destroying activity. There were no differences among treatments in heat treated cultures. It is concluded that sulphate increases thiamine-destroying activity in the rumen content and the destructive mechanism involves thermolabile factor(s), however, the ruminal synthesis of thiamine is not affected by sulphate.

Animals↗

PubMed1992

Role of thiamine status in sulphur induced polioencephalomalacia in sheep.

The effects of excess dietary sulphur were studied in sheep supplemented and unsupplemented with thiamine. The diets contained either 0.19 per cent sulphur (LS) or 0.63 per cent sulphur (HS) in combinations with 14 mg kg-1 thiamine (LB1) or 243 mg kg-1 thiamine (HB1). A total of 56 two-month-old lambs were used. Groups consisting of nine, nine, 22 and 16 lambs were fed LS-LB1, LS-HB1, HS-LB1 and HS-HB1 diets, respectively for 14 weeks. Out of 22 lambs fed the HS-LB1 diet, seven lambs developed neurological signs between the third and eighth week of the trial. Two of these lambs died, three that were in extremis were euthanased, and two recovered completely. All clinically affected animals had extensive malacic lesions in the cerebral cortex, midbrain and brainstem. None of the lambs from the LS groups or HS-HB1 group developed clinical signs. Several clinically normal lambs from the HS-LB1 group had necrotic lesions in their brains at gross and microscopic examination. Supplementation with dietary thiamine prevented development of clinical signs, but did not totally prevent development of microscopic brain lesions. Brain thiamine concentration, transketolase activity and thiamine pyrophosphate (TPP) effect were not different (P greater than 0.05) among groups. There was a strong effect (P less than 0.0001) of dietary thiamine supplementation on blood thiamine concentration and TPP effect. Blood thiamine concentration was higher whereas TPP effect was lower in the thiamine supplemented sheep. Blood and tissue thiamine concentrations in sheep exposed to high dietary sulphur did not indicate either systemic or local thiamine deficiency per se. Increased TPP effect in sheep fed the HS-LB1 diet indicated mild to moderate metabolic thiamine deficiency. Thiamine inadequacy may be an effect of an increased requirement for thiamine in animals exposed to excess dietary sulphur.

Animals↗

PubMed1991

The effects of thiamine and EDTA on biliary and urinary lead excretion in sheep.

Relative efficacy of thiamine (B1) and/or calcium disodium ethylinediaminetetraacetate (EDTA) administration on lead (Pb) excretion via bile and urine was studied in Pb-loaded sheep. The sheep were administered B1 s.c., 75 mg/kg body wt., EDTA i.v., 110 mg/kg body wt., and a combination of B1-EDTA at rates as above. Each treatment was followed by 69 h sampling of blood, bile, and urine. Urinary Pb excretion increased following B1-EDTA greater than EDTA greater than B1 administration. Thiamine and B1-EDTA treatments increased biliary Pb excretion. Overall, B1, EDTA and B1-EDTA administration increased Pb excretion via bile and urine by 72%, 595%, and 842% respectively over basal level (mean +/- SE: 20.1 +/- 2.9 micrograms Pb/h). It has been concluded that thiamine enhances elimination of Pb from the body and this feature may be beneficial in chelation therapy.

Animals↗

PubMed1991

Computer-aided design of two-dimensional electric-type hyperthermia applicators using the finite-difference time-domain method.

A hyperthermia applicator design tool consisting of a finite-difference time-domain (FDTD) technique in combination with a graphical display of electric fields and normalized linear temperature rise is described. This technique calculates, rather than assumes, antenna current distributions; it includes mutual interactions between the body and the applicator, and it calculates driving-point impedance and power delivered to the applicator. Results show that the fundamental limitation of 2-D electric-type applicators is overheating of the fat by normal components of the electric field, which exist because of near fields and capacitive coupling with the muscle. Two factors which contribute to the capacitance are the muscle conductivity and the small antenna size in air. Two examples of applicators designed to avoid fat overheating are described: a 27-MHz segmented dipole for heating large tumors to 7 cm depth, and a 100-MHz dipole for small tumors to 5 cm depth. The first uses a water bolus, and the second uses a water bolus with low-permittivity strips to reduce normal fields at the antenna ends. The results of this study describe fundamental limitations of electric field applicators, and illustrate the use of a powerful applicator design tool that allows rapid evaluation of a wide range of ideas for applicators which would require months and years to test experimentally.

Algorithms↗

PubMed1990

Multifiber gradient-index lens laser angioplasty probe.

A novel laser angioplasty probe fabricated with a gradient-index (GRIN) lens positioned at the tip of a seven-fiber bundle is presented. The combination of the GRIN lens and the fiberoptic bundle provides selectable optical directionality in either the axial direction or one of six off-axis directions for illumination of the arterial wall. The probe diameter (1 mm) is small enough for use in coronary laser angioplasty, and the probe is shown to transmit laser light and receive fluorescent signals simultaneously. In a 2 mm diameter lumen, the spot width in a plane normal to the axis of the lens is about 2 mm and the lateral spot size is approximately 10 mm long. The ability to direct the probe's beam pattern angularly should provide flexibility in both diagnosis and treatment.

Angioplasty, Balloon↗

PubMed1990

Effects of diets of high sulphur content and varied concentrations of copper, molybdenum and thiamine on in vitro phagocytic and candidacidal activity of neutrophils in sheep.

Candidacidal and phagocytic tests were performed on 34 female sheep fed high sulphur diets containing varied concentrations of thiamine, copper, and molybdenum for 14 weeks. Tests were conducted at weekly intervals for five weeks during the latter half of the experiment. The ability of polymorphonuclear leucocytes from sheep on diets unsupplemented with thiamine to kill phagocytosed Candida albicans was lower than those on diets supplemented with thiamine. The ability of polymorphonuclear leucocytes to phagocytose C albicans was lower in animals on low copper diets than in animals on high copper diets. Factorial analysis showed that thiamine supplementation significantly increased (P less than 0.0001) candidacidal but not phagocytic activity. By contrast, copper supplementation significantly increased (P less than 0.0005) the phagocytic activity with no effect on candidacidal activity. The observed detrimental effect of high sulphur intake on in vitro polymorphonuclear leucocyte function can mean that ruminants in areas where large quantities of sulphur are taken in with water and feed have compromised immune function due to lower copper and thiamine status and hence are at risk of increased susceptibility to infections.

Animal Feed↗

PubMed1990

Effects of high dietary sulfur on brain functions using evoked potentials technique.

Brain stem auditory-evoked response (BAER) is a noninvasive technique used for detecting neurophysiological abnormalities of the brain stem along the auditory pathway. Brain stem auditory-evoked response recordings were obtained from subcutaneous skin electrodes from two control sheep and 22 other sheep fed high sulfur (S) diets with low or high concentration of thiamine (B1), copper (Cu), and molybdenum (Mo). At least four peaks (I,II,III,IV) of varied amplitude were observed in all animals. Neurophysiological abnormalities due to decreased conductivity and/or excitability of nerve fibers along the auditory pathway were found on the BAER recordings of sheep fed high S diet. Abnormalities of peaks and interpeak latencies within BAER recordings were related to histopathological observations of brain stem lesions. Lesions in the areas of the cochlear nuclei and lateral lemniscus were seen in conjunction with altered BAER components. However, abnormalities in BAER recordings and lesions in the brain stem also occurred in the absence of overt clinical signs. Analysis of interpeak latencies between peaks I and IV revealed significant differences among dietary groups. Sheep given diets low in Cu, Mo, and B1 were affected most. Factorial analysis indicated B1 and interactions among Cu, Mo, and B1 as significant factors influencing interpeak latencies.

Animals↗

PubMed1989

Profiles of 67Cu in blood, bile, urine and faeces from 67Cu-primed lambs: effect of 99Mo-labelled tetrathiomolybdate on the metabolism of recently stored tissue 67Cu.

1. The relative importance of excretory routes in the removal of recently stored 67Cu following tetrathiomolybdate (TTM) administration was studied. Lambs fed on either 5 mg Cu/kg dry matter (DM) or 35 mg Cu/kg DM, were primed intravenously (iv) with 67Cu and challenged 27 h later with 99Mo-labelled TTM given either iv or intraduodenally (id). The profiles of 67Cu and 99Mo and of Cu and Mo in blood, bile, urine and faeces were measured. 2. Level of dietary Cu and route of administration of 99Mo-TTM affected the amplitude of blood, bile and urine profiles of 67Cu and stable Cu, but not the pattern of the responses observed. 3. The present study describes for the first time increased excretion of endogenous 67Cu through gastrointestinal secretions other than the bile due to TTM administration. 4. Administration of TTM resulted in the immediate release of 67Cu from storage compartments in the body into the blood circulation. Changes in stable Cu levels in blood, bile, urine and faeces, and gut and systemic effects were evident. Biliary and urinary Cu excretion due to TTM was rapid and maximal within 24 h of injection. 5. Administration of 67Cu iv resulted in the immediate excretion of 67Cu in bile in a pulsatile, constant pattern. A similar pattern of 67Cu excretion into bile in synchrony with that of 99Mo was observed after 99Mo-labelled TTM administration. 6. The similar pattern of biliary 67Cu excretion observed after injection of 67Cu and after injection of 99Mo-labelled TTM 27 h later is discussed in relation to the times required to process the Cu through different hepatic pathways for excretion in bile.

Animals↗

PubMed1989

Profiles of 67Cu in blood, bile, urine and faeces from 67Cu-primed lambs: effect of 99Mo-labelled tetrathiomolybdate on the metabolism of 67Cu after long-term storage.

1. The effectiveness of tetrathiomolybdate (TTM) in the removal of 67Cu from the long-term storage compartment in liver was studied. Lambs receiving 5 mg Cu/kg dry matter (DM) or 35 mg Cu/kg DM were primed intravenously (iv) with 67Cu and challenged 10 d later with 99Mo-labelled TTM given either iv or intraduodenally (id). The profiles of 67Cu and 99Mo and of Cu and of Mo with time were measured in blood, bile, urine and faeces. 2. The level of dietary Cu affected the amplitude of profiles of 67Cu and Cu in blood, bile and urine after administration of 99Mo-labelled TTM. TTM administration increased liver Cu removal and this was most marked in sheep given TTM iv. The liver Cu removal from the long-term storage Cu compartment was low and was not affected by the route of administration of TTM. Endogenous Cu excretion was higher in lambs given TTM id. 3. Excretion of 67Cu in bile through the transhepatocellular pathway after TTM administration appeared absent, while the transbiliary and hepatolysosomal pathways were operative. The potential reasons for this change are discussed. 4. TTM predominantly enhances the removal of Cu from the short-term storage compartment, but effects on the long-term storage compartment may still be of significance.

Animals↗

PubMed1989

Sulfur-induced polioencephalomalacia in sheep: some biochemical changes.

The effect of high dietary sulfur (S) supplementation on blood thiamine (B1) concentration, biochemical indices of liver, muscle and kidney damage and selected plasma electrolytes was studied in six sheep. Three of these sheep received an additional 230 mg thiamine/kg diet (Group 2). After approximately 2.5-3 weeks on this diet, all three sheep in the non-B1-supplemented group (Group 1) showed loss of appetite and developed mild neurological signs: depression, intermittent signs of excitation and head pressing. Increases in blood B1 concentration and plasma creatine kinase (CK) and aspartate aminotransferase (AST) were observed during this time in all affected animals. Clinical signs lasted only for two to five days. Sheep in group 2 were clinically normal throughout the experiment, but all of these animals also had elevated blood B1 concentrations and plasma CK activity at the 3 wk sampling. Plasma magnesium concentrations of group 1 sheep were elevated at the 2.5-3 wk and 6 wk samplings but they declined significantly (p less than 0.05) to low normal levels thereafter. Magnesium concentrations of group 2 sheep were low at the beginning but progressively increased during the course of the experiment. At necropsy, brain lesions suggestive of polioencephalomalacia (PEM) were observed in all sheep but were most marked in group 1. It is speculated that PEM may be caused by a direct toxic effect of S, S metabolites or B1 antimetabolites in the brain rather than by an in vivo B1 deficiency per se.

Animals↗