PubMed Health⌕ Search

Biomedical subjects

S M Richardson

Publications and source records attributed to S M Richardson.

At least 19 recordsLinked to original sources
PubMed2006

Effect of selenium supplementation and source on the selenium status of horses.

This study was conducted to determine the effect of Se supplementation and source on the Se status of horses. Eighteen 18-mo-old nonexercised horses were randomly assigned within sex to 1 of 3 treatments: 1) control (CTRL, no supplemental Se, 0.15 mg of Se/kg of total diet DM); 2) inorganic Se (INORG, CTRL + 0.45 mg of Se/kg of total diet DM from NaSeO3); or organic Se [ORG, CTRL + 0.45 mg of Se/kg of total diet DM from zinc-L-selenomethionine (Availa Se, Zinpro, Corp., Eden Prairie, MN)]. Horses were acclimated to the CTRL diet (7.1 kg of DM alfalfa hay and 1.2 kg of DM concentrate per horse daily) for 28 d. After the acclimation period, the appropriate treatment was top-dressed on the individually fed concentrate for 56 d. Jugular venous blood samples were collected on d 0, 28, and 56. Middle gluteal muscle biopsies were collected on d 0 and 56. Muscle and plasma were analyzed for Se concentrations. Glutathione peroxidase activity was measured in muscle (M GPx-1), plasma (P GPx-3), and red blood cells (RBC GPx-1). Data were analyzed as a repeated measures design. Mean plasma Se concentration on d 28 and 56 was greater (P < 0.05) for Se-supplemented horses compared with CTRL horses, and tended (P < 0.1) to be greater in ORG vs. INORG on d 28. Mean muscle Se concentration and P GPx-3 activities increased (P < 0.05) from d 0 to 56 but were not affected by treatment. Mean RBC GPx-1 activity tended to be greater (P < 0.1) in ORG than INORG or CTRL horses on d 28, and tended to be greater (P < 0.1) for INORG compared with ORG horses on d 56. Mean RBC GPx-1 activity of INORG and ORG horses was not different from that of CTRL on d 56. Mean M GPx-1 activity decreased (P < 0.01) from d 0 to 56. In conclusion, zinc-L-selenomethionine was more effective than NaSeO3 at increasing plasma Se concentration from d 0 to 28; however, both supplemental Se sources had a similar effect by d 56. No difference in Se status due to Se supplementation or source could be detected over a 56-d supplementation period by monitoring middle gluteal muscle Se, M GPx-1, or P GPx-3. Results for RBC GPx-1 also were inconclusive relative to the effect of Se supplementation and source.

Animal Feed↗
PubMed2003

3-Morpholinosyndnonimine inhibits 5-hydroxytryptamine-induced phosphorylation of nitric oxide synthase in endothelial cells.

5-Hydroxytryptamine (5-HT) is a vasoactive substance that is taken up by endothelial cells to activate endothelial nitrite oxide synthase (eNOS). The activation of eNOS results in the production of nitric oxide (NO), which is responsible for vasodilation of blood vessels. NO also interacts with superoxide anion (O2*-) to form peroxynitrite (ONOO-), a potent oxidant that has been shown to induce vascular endothelial dysfunction. We examined the ability of 3-morpholinosyndnonimine (SIN-1), an ONOO- generator, to inhibit 5-HT-induced phosphorylation of eNOS in cultured bovine aortic endothelial cells (BAECs). We observed that 5-HT phosphorylates Ser1179 eNOS in a time- and concentration-dependent manner. Maximum phosphorylation occurred at 30 sec using a concentration of 1.0 microM 5-HT. BAECs treated with SIN-1 (1-1000 microM) for 30 min showed no significant increase in eNOS phosphorylation. However, 5-HT-induced eNOS phosphorylation was inhibited in cells treated with various concentrations of SIN-1 for 30 min and stimulated with 5-HT. These data suggest that an increase in ONOO- as a result of an increase in the production of O2*-, may feedback to inhibit 5-HT-induced eNOS phosphorylation at Ser1179 and therefore, contribute to endothelial dysfunction associated with cardiovascular diseases.

Animals↗
PubMed1994

Purification of crystallizable recombinant SIVmac251-32H proteinase.

We have cloned a simian immunodeficiency virus (SIV) proteinase gene directly from proviral DNA of the infectious viral stock SIVmac251-32H (11/88 pool). The deduced amino acid sequence from this proteinase gene is similar to that for the published SIVmac239 molecular clone. SIVmac251-32H proteinase (SIV PR) and its flanking pol sequences were expressed in Escherichia coli as a fusion protein with most of the T7 bacteriophage gene 10 protein. The expressed protein formed cytoplasmic inclusion bodies which were solubilized in 8 M urea, and the recombinant SIV PR was refolded, yielding active, self-processed enzyme. The SIV PR was purified to homogeneity using a single pepstatin A affinity chromatography step, and had a specific peptidolytic activity of 20 mumol/min/mg. Enzymatic characteristics similar to those previously documented for other immunodeficiency virus proteinases (EC 3.4.23) were observed. These include an acidic pH optimum (pH 5.3), sensitivity to sodium chloride concentration, and complete inhibition by pepstatin A. In addition to these properties we have observed quantitative crystallization from low protein concentrations. We describe the first crystal habit for the proteinase from the HIV-2/SIV class of immunodeficiency virus, which is distinctly different from that for HIV-1 proteinase crystals.

Amino Acid Sequence↗
PubMed1994

Expression vectors for the construction of hybrid Ty-VLPs.

Purification of expressed proteins can be facilitated by expressing the recombinant protein as a fusion with a carrier protein that assembles into particulate structures. This article describes the use of expression vectors in producing a hybrid of the yeast retrotransposon Ty, which self-assembles into virus-like particles (VLPs). Hybrid VLPs can be used in such laboratory applications as the production of polyclonal and monoclonal antibodies, structure/function analyses, the detection of important antigenic determinants, and epitope mapping of monoclonal antibodies.

Biotechnology↗
PubMed1993

Continuous flow resectoscopes. Are the theory and design wrong?

The optical design of rod-lens telescopes has now reached a zenith. The only way of improving the resectoscope is to investigate the ergonomics and flow dynamics. We present a comparative analysis of the flow mechanics of continuous flow resectoscopes. The morphology, flow characteristics and irrigating potential (washout gradient) of several instruments were examined. It was found that when used with balanced continuous flow (inflow and outflow balanced), all of the endoscopes had poor visibility compared with unbalanced continuous flow (inflow > outflow). Possible changes in the design of the instruments are discussed.

Endoscopes↗
PubMed1992

Symmetry, flexibility and permeability in the structure of yeast retrotransposon virus-like particles.

The virus-like particles (VLPs) of the yeast retrotransposon Ty are genetically, structurally and functionally analogous to retroviral nucleocapsids or cores. Like retroviral cores Ty-VLPs package and possibly promote the enzyme activities for reverse transcription and integration, as well as encapsulating the RNA that is the intermediate in retrotransposition. Here we show that Ty-VLPs assemble into symmetrical structures across a broad distribution of particle sizes. This spread of sizes violates the principle of quasi-equivalent packing. In addition, RNase accessibility experiments suggest that these particles form an open structure that does not protect the encapsulated RNA. These features distinguish Ty-VLPs from typical spherical viral capsids in both structure and function.

DNA Transposable Elements↗
PubMed1992

Dynamic clearance: mathematical assessment of flow mechanics in prostatic resection.

The understanding of flow mechanics in endoscopy is poor. In prostatic surgery, emphasis has been placed on limiting the rise of intravesical pressure with little regard to the effect on flow mechanics and visibility. A model has been developed using dynamic clearance to compare different methods of prostatic resection. The results show that in a 0.95-cm glass urethra, continuous flow irrigation has slower clearance at all flow rates when compared with intermittent irrigation and suprapubic suction. Although intravesical pressure is important, attention should also be paid to flow dynamics and more emphasis should be placed on this when new instruments and fluid delivery systems are developed.

Endoscopy↗
PubMed1992

Flow visualization in uroendoscopy: the steal effect.

Balanced continuous flow resection has been offered as the best form of irrigation in uroendoscopy. Although it will keep the bladder pressure low, using flow visualization techniques it has been demonstrated that it does not fulfil the requirements of an irrigating fluid when used in a confined environment such as the prostatic urethra. The outflowing irrigating fluid has been shown to be taken directly from the inflowing jet ('steal effect') thereby reducing the effectiveness of the irrigating jet on the working area of the resectoscope.

Endoscopes↗
PubMed1992

Evaluation of an enzyme-linked immunosorbent assay for the detection of antibodies to caprine arthritis-encephalitis virus in goat serum.

An indirect enzyme-linked immunosorbent assay (ELISA), was evaluated for its ability to detect serum antibodies against caprine arthritis-encephalitis virus (CAEV). The ELISA was compared to three other serological immunoassays, agar gel immunodiffusion test (AGIDT), immunoblot assay (IBA), and a fixed-cell immunoperoxidase assay (FCIPA). A total of 511 samples, from 40 farms representing a variety of goat breeds and ages were tested. An estimate of the ELISA sensitivity and specificity was made, relative to combined test results of the three other CAEV serological assays. The degree of agreement of test results among these four assays was evaluated. The number of positives detected by the ELISA, AGIDT, IBA and IPA tests was 193, 154, 204 and 163, respectively. Of the 511 sera tested, 172 were positive to any two or all three of these tests, and were defined as reference positive. A total of 237 samples were negative to all three reference tests, and were defined as reference negative. Relative to these references, the ELISA had a point estimate of 98.3% sensitivity and 97.9% specificity. There was good agreement between the ELISA and the other three assays with a kappa statistic of agreement greater than 0.7 for all three comparisons. The ELISA is therefore considered a suitable assay, with high sensitivity and specificity, for detection of antibodies to CAEV in serum.

Animals↗
PubMed1988

The helical repeat of underwound DNA in solution.

Closed circular DNA was relaxed with a topoisomerase in the presence of varying concentrations of the intercalating dye, ethidium bromide, to create underwound, planar DNA rings. We directly determined the helical repeat of these DNA molecules by the Gaussian center method and found that it varied as a simple predicted function of the degree of underwinding and the helical repeat of relaxed, dye-free DNA. We discuss these results in light of a recent mathematical treatment of DNA structure which predicts that the helical repeat of supercoiled DNA molecules in solution obeys the same function.

DNA, Circular↗
PubMed1988

DNA supercoiling and the leu-500 promoter mutation of Salmonella typhimurium.

DNA supercoiling is an important, but relatively poorly understood factor which influences promoter function. leu-500 is a point mutation in the promoter of the leucine operon of Salmonella typhimurium which confers leucine auxotrophy. It can be phenotypically suppressed by mutations in the topA gene, which encodes topoisomerase I, implicating DNA supercoiling in the regulation of this promoter. We have demonstrated that phenotypic suppression of this mutant promoter is transcriptional, and that topA mutations restore function to the mutant promoter. Transcription from the leu-500 promoter was examined in a series of strains harbouring topA and tos (presumptive gyr) mutations, each of which exhibits a different level of in vivo plasmid supercoiling. Promoter function did not correlate with the level of supercoiling but rather with the presence or absence of a functional topA gene. Furthermore, when cloned onto a multicopy plasmid, the leu-500 promoter failed to function, even in a topA background. Thus, local rather than global changes in DNA topology are implicated in the activation of this promoter.

Bacterial Proteins↗
PubMed1987

The case for a wet, warm climate on early Mars.

Theoretical arguments are presented in support of the idea that Mars possessed a dense CO2 atmosphere and a wet, warm climate early in its history. Calculations with a one-dimensional radiative-convective climate model indicate that CO2 pressures between 1 and 5 bars would have been required to keep the surface temperature above the freezing point of water early in the planet's history. The higher value corresponds to globally and orbitally averaged conditions and a 30% reduction in solar luminosity; the lower value corresponds to conditions at the equator during perihelion at times of high orbital eccentricity and the same reduced solar luminosity. The plausibility of such a CO2 greenhouse is tested by formulating a simple model of the CO2 geochemical cycle on early Mars. By appropriately scaling the rate of silicate weathering on present Earth, we estimate a weathering time constant of the order of several times 10(7) years for early Mars. Thus, a dense atmosphere could have persisted for a geologically significant time period (approximately 10(9) years) only if atmospheric CO2 was being continuously resupplied. The most likely mechanism by which this might have been accomplished is the thermal decomposition of carbonate rocks induced directly and indirectly (through burial) by intense, global-scale volcanism. For plausible values of the early heat flux, the recycling time constant is also of the order of several times 10(7) years. The amount of CO2 dissolved in standing bodies of water was probably small; thus, the total surficial CO2 inventory required to maintain these conditions was approximately 2 to 10 bars. The amount of CO2 in Mars' atmosphere would eventually have dwindled, and the climate cooled, as the planet's internal heat engine ran down. A test for this theory will be provided by spectroscopic searches for carbonates in Mars' crust.

Atmosphere↗
PubMed1986

A hybrid model of the CO2 geochemical cycle and its application to large impact events.

A hybrid model of the carbonate-silicate geochemical cycle is presented which is capable of calculating the partitioning of carbon dioxide between the atmosphere, ocean, and sedimentary rocks. The ocean is subdivided into a shallow, mixed layer, which remains in equilibrium with the atmosphere, and a massive, deep layer which does not. Gradients in dissolved carbon content are established between the mixed layer and the deep ocean as a consequence of downward fluxes of fecal matter and of dead planktonic organisms. The dissolved carbon content and alkalinity of the ocean as a whole are controlled by weathering and metamorphism of sedimentary rocks. Equilibrium solutions are derived for the preindustrial atmosphere/ocean system and for a system that may be similar to that existing during the Late Cretaceous Period. The model is then used to determine how the modern and ancient marine biospheres might be affected by an oceanic impact of a large asteroid or comet. Such an event could perturb the carbon cycle in several different ways. Global darkening caused by stratospheric dust veil could destroy most of the existing phytoplankton in a period of several weeks to several months. At the same time, dissolution of atmospheric NOx compounds synthesized during the impact would lower the pH of ocean surface waters and release CO2 into the atmosphere. Both effects might be enhanced by an influx of CO2 released from upwelling of deep ocean water near the hot impact site, from oxidation of dead organic matter, and from the comet itself. The net result could be to raise surface temperatures by several degrees and to make the surface ocean uninhabitable by calcareous organisms for as much as 20 yrs (the time scale for mixing with deep ocean). It appears unlikely, however, that an impact could create a "Strangelove ocean," in which surface waters remained corrosive to calcium carbonate for thousands or tens of thousands of years. Thus, disruption of the carbon cycle by an impact event cannot by itself explain the scarcity of calcium carbonate in sediments found within the first few centimeters above the K/T boundary.

Atmosphere↗
PubMed1985

Seafloor hydrothermal activity and spreading rates: the Eocene carbon dioxide greenhouse revisted.

A suggestion has been made that enhanced rates of hydrothermal activity during the Eocene could have caused a global warming by adding calcium to the ocean and pumping CO2 into the atmosphere (Owen and Rea, 1984). This phenomenon was purported to be consistent with the predictions of the CO2 geochemical cycle model of Berner, Lasaga and Garrels (1983) (henceforth BLAG). In fact, however, the BLAG model predicts only a weak connection between hydrothermal activity and atmospheric CO2 levels. By contrast, it predicts a strong correlation between seafloor spreading rates and pCO2, since the release rate of CO2 from carbonate metamorphism is assumed to be proportional to the mean spreading rate. The Ecocene warming can be conveniently explained if the BLAG model is extended by assuming that the rate of carbonate metamorphism is also proportional to the total length of the midocean ridges from which the spreading originates.

Atmosphere↗
PubMed1984

The genetic control of DNA supercoiling in Salmonella typhimurium.

We have elucidated the genetic control of DNA supercoiling in Salmonella typhimurium. The level of superhelix density is controlled by two classes of genes. The only member of the first class is topA, the structural gene for topoisomerase I. The second class, tos, (topoisomerase one suppressor) consists of at least two genes, one of which is linked to gyrA, the structural gene for the topoisomerase subunit of DNA gyrase. Deletions of topA result in oversupercoiling of plasmid DNA. These mutations do not require the acquisition of second-site compensatory mutations to allow cell growth, in contrast to the situation in Escherichia coli. However, tos mutations, unlinked to topA, have been isolated which reduce plasmid superhelix density. We conclude that the level of DNA supercoiling in S. typhimurium is a dynamic balance between the effects of the gene products of topA (relaxation) and tos (supercoiling) which act independently of each other. Using a variety of combinations of these mutations we have constructed a series of isogenic strains, each of which has a different but precisely defined level of plasmid supercoiling; the series as a whole provides a wide range of supercoiling both above and below the wild-type level.

Bacterial Proteins↗
PubMed1984

Water loss on Venus: the role of carbon monoxide.

The abundance of water on Venus is four to five orders of magnitude lower than on the Earth. This difference may reflect initial differences in the bulk volatile contents of the two planets, or may be the result of processes for massive water loss on Venus. A series of thermodynamic calculations are performed on the heterogeneous system C-O-H-N-S, varying C/H upward from its terrestrial value of 0.033 in order to evaluate the extent to which either of these two possibilities may account for the low water content on Venus. Relative abundances of 84 molecular gaseous species are computed as functions of temperature, total pressure, oxygen fugacity, and bulk C/H. As bulk C/H increases, the complement of atmospheric H2O decreases, but C/H would have to be raised to an improbably high value to account for the low water abundance on Venus by initial deficiency alone. Increasing C/H also results in a rapid increase in CO/H2O, however, and enhances water loss by the reaction CO + H2O = CO2 + H2 or by reaction of carbon monoxide with the free oxygen liberated by photodissociation of water. Other water loss mechanisms have relied on crustal FeO as an oxygen sink. Such mechanisms, however, should have operated on both Venus and the Earth and may be insufficient to account for the major differences in present H2O abundance between the two planets. Calculations performed in this study suggest that if the outgassed C/H on Venus was higher than on Earth by even less than a factor of 5, it would have been sufficient to make carbon monoxide competitive with FeO as a sink for oxygen. Together with the lower initial water abundance that follows from a higher C/H, water loss involving CO may have been a major factor in determining the present low abundance of water on Venus.

Atmosphere↗