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Biomedical subjects

C R Stewart

Publications and source records attributed to C R Stewart.

At least 19 recordsLinked to original sources
PubMed2001

Knowledge of Down syndrome in pregnant women from different ethnic groups.

The uptake of any screening test is influenced by knowledge of the condition being screened for. In the present study, the knowledge and the source of knowledge of women offered antenatal screening for Down syndrome (DS) was assessed by means of a self-administered questionnaire. The questionnaire was administered to 300 consecutive women booking for antenatal care, of the 245 (82%) women who completed and returned the questionnaire, 117 (48%) were Caucasian, 85 (35%) were Asian born outside the UK, 32 (13%) were Asian born in the UK and ten (4%) belonged to other categories. Only 30% of the cohort had a good understanding of the condition. Racial groups other than Caucasian had a poorer understanding of DS. The factors which affected knowledge of DS included quality of spoken English, knowing an affected child, parity and religion. The most significant factor affecting acceptance of screening was the woman's knowledge of DS. The source of information for the condition varied widely: 42% from a general practitioners (GP), 24% from the hospital and 16% from midwives. The proportion with good knowledge was similar in those women whose source of information was the GP (45%) and the midwife (41%). These proportions were, however, higher (though not significantly) when the source of information was from magazines and newspapers (67%) and from friends (53%). Uptake of the screening test was best in those with good knowledge (53%) compared to those with poor knowledge (23%) (p<0.02). Between 28% and 66% (depending on the ethnic group) of women had a screening blood test "allegedly" without knowing why it had been performed. In order to improve uptake of the screening test for DS there is need for better education and counselling of women attending for antenatal care.

Adolescent↗
PubMed2001

The effects of magnesium supplementation on exercise performance.

PURPOSE: To determine the effects of magnesium (Mg2+) supplementation on performance and recovery in physically active women using the sensitive and recently advanced measure of ionic Mg2+ (iMg). METHODS: Participants (N = 121) were screened for [iMg] in plasma, with 44 (36.4%) exhibiting [iMg] below the normal range of 0.53-0.67 mmol.L-1 (4). Thirty-two subjects (21 +/- 3 yr) representing a broad range of [iMg] (0.54 +/- 0.04 mmol.L-1) completed the main 14-wk study. At baseline, participants submitted to a resting blood pressure measurement, and they completed both an anaerobic treadmill test and an incremental (aerobic) treadmill test. For the latter, values for workload, oxygen uptake, and heart rate were obtained at both anaerobic threshold and maximal effort. Blood samples for iMg, total serum Mg2+ (TMg), erythrocyte Mg2+ (EMg), Ca2+, K+, Na+, hemoglobin, hematocrit, lactate, and glucose were also collected pretest, and 4, 10, 30 min, and 24 h posttest. Subjects received 212 mg.d-1 Mg oxide or placebo in a double-blind fashion and were retested after 4 wk. After a 6-wk washout period, the testing was repeated with a treatment crossover. RESULTS: Ionic Mg2+ increased with Mg2+ treatment versus placebo (P < 0.05); however, performance and recovery indices were not significantly affected. CONCLUSION: Four weeks of 212 mg.d-1 Mg oxide supplementation improves resting [iMg] levels but not performance or recovery in physically active women.

Adolescent↗
PubMed1998

Genes and regulatory sites of the "host-takeover module" in the terminal redundancy of Bacillus subtilis bacteriophage SPO1.

Early in infection of Bacillus subtilis by bacteriophage SPO1, the synthesis of most host-specific macromolecules is replaced by the corresponding phage-specific biosyntheses. It is believed that this subversion of the host biosynthetic machinery is accomplished primarily by a cluster of early genes in the SPO1 terminal redundancy. Here we analyze the nucleotide sequence of this 11.5-kb "host-takeover module," which appears to be designed for particularly efficient expression. Promoters, ribosome-binding sites, and codon usage statistics all show characteristics known to be associated with efficient function in B. subtilis. The promoters and ribosome-binding sites have additional conserved features which are not characteristic of their host counterparts and which may be important for competition with host genes for the cellular biosynthetic machinery. The module includes 24 genes, tightly packed into 12 operons driven by the previously identified early promoters PE1 to PE12. The genes are smaller than average, with half of them having fewer than 100 codons. Most of their inferred products show little similarity to known proteins, although zinc finger, trans-membrane, and RNA polymerase-binding domains were identified. Transcription-termination and RNase III cleavage sites were found at appropriate locations.

Amino Acid Sequence↗
PubMed1998

A comparative study of women with chronic pelvic pain, chronic nonpelvic pain and those with no history of pain attending general practitioners.

OBJECTIVE: To investigate and compare the demographic and psychosocial profiles of women with chronic pelvic pain, chronic pain in a different site, and those with no history of pain with specific reference to a history of sexual abuse. DESIGN: A prospective comparative study. SETTING: Pelvic Pain Clinic at Leicester General Hospital NHS Trust, Pain Management Clinic at Leicester Royal Infirmary NHS Trust and two General Practices. PARTICIPANTS: Thirty women with chronic pelvic pain, 30 women with chronic pain in a different site and 30 women attending their general practitioner with no history of pain. INTERVENTIONS: A specifically designed patient profile questionnaire to identify and explore incidents of sexual and physical abuse was administered to each woman by a research psychologist for confidential self-completion. Data were also collected on other demographic, medical and psychosocial characteristics. RESULTS: Women with chronic pelvic pain were found to have a higher lifetime prevalence of sexual abuse, involving penetration or other genital contact compared with the two comparison groups. The prevalence of physical abuse was the same in all groups. Women in the pelvic pain group were more likely to have approached their GP for symptoms not related to pelvic pain than women in the other two groups and the incidence of clinical anxiety was significantly higher in this group compared with the pain-free group. The prevalence of sexual problems was much higher in the group with pelvic pain compared with the other two groups. CONCLUSION: These findings indicate that women with chronic pelvic pain have a higher incidence of past sexual abuse compared with women in a comparison pain group and with women with no pain.

Adolescent↗
PubMed1995

Genes that protect against the host-killing activity of the E3 protein of Bacillus subtilis bacteriophage SPO1.

A cloned rpoB gene, specifying an apparently mutant RNA polymerase beta subunit, protected Escherichia coli against the cytocidal effects of the E3 protein of bacteriophage SPO1, suggesting that RNA polymerase is the primary cellular target of the E3 protein. Two segments of the wild-type E. coli genome, one of which specifies a suppressor of dnaK mutations, and thus, possibly, a molecular chaperone, also provided protection when overexpressed, but wild-type rpoB did not.

Bacillus Phages↗
PubMed1993

A cytotoxic early gene of Bacillus subtilis bacteriophage SPO1.

Some of the early genes of Bacillus subtilis bacteriophage SPO1 were hypothesized to function in the shutoff of host biosyntheses. Two of these genes, e3 and e22, were cloned and sequenced. E22 showed no similarity to any known protein, while E3, a highly acidic protein, showed significant similarity only to other similarly acidic proteins. Each gene was immediately downstream of a very active early promoter. Each was expressed actively during the first few minutes of infection and was then rapidly shut off and its RNA rapidly degraded. An e3 nonsense mutation severely retarded the degradation of e3 RNA. Expression of a plasmid-borne e3 gene, in either B. subtilis or Escherichia coli, resulted in the inhibition of host DNA, RNA, and protein syntheses and prevented colony formation. However, the e3 nonsense mutation caused no measurable decrease in either burst size or host shutoff during infection and, in fact, caused an increased burst size at high multiplicities of infection. We suggest that e3 is one of several genes involved in host shutoff, that its function is dispensable both for host shutoff and for phage multiplication, and that its shutoff function is not entirely specific to host activities.

Amino Acid Sequence↗
PubMed1993

Proptosis as a presenting sign of extradural haematoma.

A conscious 15-year-old boy presented with progressive proptosis and a severe headache 2 weeks after minor blunt trauma to the head. No neurological deficit was present. Computed tomography demonstrated intracranial and intraorbital cyst-like masses. At craniotomy a subacute extradural haematoma was found which communicated with an orbital subperiosteal haematoma through a shelved orbital roof fracture. The haematomas were drained and the patient made an uneventful postoperative recovery. Although rare, an extradural haemorrhage should be considered in any patient presenting to an ophthalmologist with progressive proptosis and headache following a head injury.

Adolescent↗
PubMed1992

cDNA clones encoding Arabidopsis thaliana and Zea mays mitochondrial chaperonin HSP60 and gene expression during seed germination and heat shock.

Mitochondria contain a nuclear-encoded heat shock protein, HSP60, which functions as a chaperonin in the post-translational assembly of multimeric proteins encoded by both nuclear and mitochondrial genes. We have isolated and sequenced full-length complementary DNAs coding for this mitochondrial chaperonin in Arabidopsis thaliana and Zea mays. Southern-blot analysis indicates the presence of a single hsp60 gene in the genome of A. thaliana. There is a high degree of homology at the predicted amino acid levels (43 to 60%) between plant HSP60s and their homologues in prokaryotes and other eukaryotes which indicates that these proteins must have similar evolutionarily conserved functions in all organisms. Northern- and western-blot analyses indicate that the expression of the hsp60 gene is developmentally regulated during seed germination. It is also heat-inducible. Developmental regulation of the (beta-subunit of F1-ATPase, an enzyme complex that is involved in the cyanide-sensitive mitochondrial electron transport system, indicates that imbibed embryos undergo rapid mitochondrial biogenesis through the early stages of germination. Based on the functional role of HSP60 in macromolecular assembly, these data collectively suggest that the presence of higher levels of HSP60 is necessary during active mitochondrial biogenesis, when the need for this protein is greatest in assisting the rapid assembly of the oligomeric protein structures.

Amino Acid Sequence↗
PubMed1992

Photosynthesis and photorespiration in presenescent, senescent, and rejuvenated soybean cotyledons.

Various growth and physiological parameters were measured in germinating, presenescent, and senescing soybean (Glycine max [L.] Merr.) cotyledons and in cotyledons rejuvenated by epicotyl removal 18 days after planting. The maximal measured carbon dioxide exchange rates (CER) in the cotyledons were in the range of those reported for field-grown soybean leaves. Rejuvenated cotyledons accumulated total chlorophyll in excess of the maximum observed in presenescent cotyledons. When photosynthetic rates were expressed per cotyledon, the CER in rejuvenated tissue recovered to the maximal rates observed in presenescent cotyledons. Ribulose-1,5-bisphosphate carboxylase/oxygenase in rejuvenated cotyledons also recovered to the maximal amount seen in presenescent cotyledons so that CER appeared to be a function of ribulose-1,5-bisphosphate carboxylase/oxygenase content during most of the period studied. Observations of the postillumination outburst of CO(2) and (14)C label in glycine indicated that photorespiration was occurring in the cotyledons and that photorespiration relative to photosynthesis was different in rejuvenated compared with presenescent cotyledons.

Journal Article↗
PubMed1992

Effect of Exogenous Abscisic Acid on Proline Dehydrogenase Activity in Maize (Zea mays L.).

Plant responses to drought stress include proline and abscisic acid (ABA) accumulation. Proline dehydrogenase (PDH) (EC 1.4.3) is the first enzyme in the proline oxidation pathway, and its activity has been shown to decline in response to water stress (PJ Rayapati, CR Stewart [1991] Plant Physiol 95: 787-791). In this investigation, we determined whether ABA treatment affects PDH activity in a manner similar to drought stress in maize (Zea mays L.) seedlings. Four exogenous ABA treatments (0, 11, 33, and 100 micromolar ABA) were applied to well-watered maize seedlings. Mitochondria were isolated and PDH was solubilized using Nonidet P-40. PDH activity was measured by the reduction of iodonitrotetrazolium violet under proline-dependent conditions. There was no effect of ABA on PDH activity at 33 and 100 micromolar ABA, but there was a 38% decline at 11 micromolar. This decline was less than the 69% reduction in activity under drought stress. Endogenous ABA determinations and plant growth rate showed that ABA entered the plant and was affecting metabolic processes. ABA treatments had a small effect on shoot and root proline concentration, whereas drought stress caused a 220% increase in root tissues. We conclude that ABA is not part of the pathway linking drought stress and decreased PDH activity.

Journal Article↗
PubMed1991

Solubilization of a Proline Dehydrogenase from Maize (Zea mays L.) Mitochondria.

L-Proline is oxidized to pyrroline-5-carboxylic acid in intact plant mitochondria by a proline dehydrogenase (EC 1.4.3) that is bound to the matrix side of the inner mitochondrial membrane (TE Elthon, CR Stewart [1981] Plant Physiol 67: 780-784). This investigation reports the first solubilization of the L-proline dehydrogenase (PDH) from plant mitochondria. The supernatant from NP-40-treated etiolated shoot mitochondria of maize, Zea mays L., reduced iodonitrotetrazolium violet in a proline dependent manner. The pH optimum for this activity was 8. The apparent K(m) for proline was 6.6 millimolar. When supplied with proline, this solubilized PDH activity also synthesized pyrroline-5-carboxylic acid. The PDH activity was inhibited in vitro by 300 millimolar potassium chloride but not by 300 millimolar potassium acetate. The PDH activity had a molecular mass that was greater than 150 kilodaltons. Mitochondria were prepared from etiolated shoots grown in 100% water-saturated vermiculite (control) and 16% water-saturated vermiculite (stress). The specific activity of solubilized PDH from the stress treatment was 11% of the same activity from the control treatment. Oxygen uptake in the presence of proline and ADP (state 3 proline oxidation) by mitochondria from the stress treatment was 25% of the same rate by mitochondria from the control treatment. Mitochondria were also prepared 16 hours after rewatering the seedlings growing in the stress treatment. Both the solubilized PDH specific activity and state 3 proline oxidation returned to the control levels. The specific activities of the NAD(+)-dependent pyrroline-5-carboxylic acid dehydrogenase and cytochrome c oxidase in the solubilized preparations were unaffected by these stress and recovery treatments. Oxygen uptake rates by intact mitochondria in the presence of ADP and NADH, succinate or malate-pyruvate were also unaffected by these treatments.

Journal Article↗
PubMed1990

Respiration and Alternative Oxidase in Corn Seedling Tissues during Germination at Different Temperatures.

Respiration rates of Zea mays L. seedling tissues grown at 30 and 14 degrees C were measured at 25 degrees C at different stages of seedling growth. Accumulation of heat units was used to define the developmental stages to compare respiration between the two temperatures. At both temperatures, respiration rates of most tissues were highest at the youngest stages, then declined with age. Respiration rates of mesocotyl tissue were the most responsive to temperature, being nearly twofold higher when grown at 14 compared to 30 degrees C. Alternative pathway respiration increased concomitantly with respiration and was higher in mesocotyls grown in the cold. When seedlings were started at 30 then transferred to 14 degrees C, the increase in alternative pathway respiration due to cold was not observed unless the seedlings were transferred before 2 days of growth. Seedlings transferred to 14 degrees C after growth at 30 degrees C for 2 days had the same alternative oxidase capacity as seedlings grown at 30 degrees C. Seedlings grown at 14 degrees C for 10 to 12 days, then transferred to 30 degrees C, lost alternative pathway respiratory capacity over a period of 2 to 3 days. Western blots of mitochondrial proteins indicated that this loss of capacity was due to a loss of the alternative oxidase protein. Some in vitro characteristics of mitochondria were determined. The temperature optimum for measurement of alternative oxidase capacity was 15 to 20 degrees C. At 41 degrees C, very little alternative oxidase was measured, i.e., the mitochondrial oxygen uptake was almost completely sensitive to cyanide. This inactivation at 41 degrees C was reversible. After incubation at 41 degrees C, the alternative oxidase capacity measured at 25 degrees C was the similar to when it was measured at that temperature directly. Isolated mitochondria lost alternative oxidase capacity at the same rate when incubated at 41 degrees C as they did when incubated at 25 degrees C. Increasing the supply of electrons to isolated mitochondria increased the degree of engagement of the alternative pathway, whereas lower temperature decreased the degree of engagement. Lower temperatures did not increase the degree of engagement of the pathway in intact tissues. We interpret these observations to indicate that the greater capacity of alternative oxidase in cold-grown seedlings is a consequence of development at these low temperatures which results in elevated respiration rates. Low temperature itself does not cause greater capacity or engagement of the alternative oxidase in mitochondria that have developed under warm temperatures. Our hypothesis would be that the low growth temperatures require the seedlings to have a higher respiration rate for some reason, e.g., to prevent the accumulation of a toxic metabolite, and that the alternative pathway functions in that respiration.

Journal Article↗
PubMed1990

Seedling growth, mitochondrial characteristics, and alternative respiratory capacity of corn genotypes differing in cold tolerance.

Four maize (Zea mays L.) inbreds representing genetic differences in seedling cold tolerance were used to determine the effect of growth temperatures on dry weight accumulation and mitochondrial properties, especially the alternative oxidase capacity. Seedlings were grown in darkness at 30 degrees C (constant), 14 degrees C (constant), and 15 degrees C for 16 hours and 8 degrees C for 8 hours. Inbreds B73 and B49 were characterized as cold tolerant while G50 and G84 were cold sensitive. Shoot growth rate of cold-sensitive inbreds in the lower temperatures was slower relative to the tolerant inbreds. Mesocotyl tissue was particularly sensitive to low temperatures during growth after germination. There were no significant differences in relative rates of mitochondrial respiration in the cold-tolerant compared to cold-sensitive inbreds measured at 25 degrees C. Mitochondria from all seedlings grown at all temperatures had the ability to phosphorylate as indicated by the observation of respiratory control. This result indicated that differences in low temperature growth were probably not related to mitochondrial function at low temperatures. Alternative oxidase capacity was higher in mitochondria from seedlings of all inbreds grown at 14 degrees C compared to 30 degrees C. Capacities in seedlings of 14 degrees C-grown B73 and G50 were higher than in B49 and G84. Capacities in seedlings grown for 16 hours at 15 degrees C and 8 hours at 8 degrees C were similar to those from 14 degrees C-grown except in G50 which was lower and similar to those grown at 30 degrees C. Mesocotyl tissue was the most responsive tissue to low growth temperature. Coleoptile plus leaf tissue responded similarly but contained lower capacities. Antibody probing of western blots of mitochondrial proteins confirmed that differences in alternative oxidase capacities were due to differences in levels of the alternative oxidase protein. Male sterile lines of B73 were also grown under the three different temperature regimes. These lines grew equally as well as the normal B73 at all temperatures and the response of alternative oxidase capacity and protein to low growth temperature was similar to normal B73.

Journal Article↗
PubMed1989

The determination of (-)-(S)- and (+)-(R)-ifosfamide in plasma using enantioselective gas chromatography: a validated assay for pharmacokinetic and clinical studies.

An enantioselective gas chromatographic method has been developed and validated for the determination of the plasma concentration of the enantiomers of the anticancer drug ifosfamide (IFF). In this approach, the IFF enantiomers are separated from the plasma matrix by solid phase extraction, chromatographically resolved by gas chromatography on a chiral stationary phase, and detected by mass selective detection using selective ion monitoring. The assay has been validated for routine clinical and pharmacokinetic use and has a limit of detection in plasma of 250 ng/ml of each isomer.

Chromatography, Gas↗
PubMed1989

Evaluation of an automatic method of measuring features of motor unit action potentials.

This study was performed to evaluate an automatic method of motor unit action potential (MUAP) analysis developed in our laboratory. MUAPs were recorded from the biceps brachii muscle of 68 normal subjects and 122 patients with nerve or muscle disease. The values of mean MUAP durations from normal subjects obtained by automatic analysis were similar to those reported in the literature. However, the normal range of MUAP amplitude and the incidence of polyphasic MUAPs were much higher. Normal ranges of mean MUAP area, area/amplitude ratio, and the number of turns were also defined. Automatic analysis demonstrated an abnormality of at least one MUAP feature in 70% of patients. There was concordance between automated analysis and visual assessment of MUAPs in 76% of patients with neuropathy but in only 50% of patients with myopathy. The relationships between different MUAP features seen in neuropathy and myopathy are explained in physiologic terms.

Action Potentials↗
PubMed1989

Pyrroline-5-Carboxylate Reductase Is in Pea (Pisum sativum L.) Leaf Chloroplasts.

Proline accumulation is a well-known response to water deficits in leaves. The primary cause of accumulation is proline synthesis. Delta(1)-Pyrroline-5-carboxylate reductase (PCR) catalyzes the final reaction of proline synthesis. To determine the subcellular location of PCR, protoplasts were made from leaves of Pisum sativum L., lysed, and fractionated by differential and Percoll density gradient centrifugation. PCR activity comigrated on the gradient with the activity of the chloroplast stromal marker NADPH-dependent triose phosphate dehydrogenase. We conclude that PCR is located in chloroplasts, and therefore that chloroplasts can synthesize proline. PCR activities from chloroplasts and etiolated shoots were compared. PCR activity from both extracts is stimulated at least twofold by 100 millimolar KCl or 10 millimolar MgCl(2). The pH profiles of PCR activity from both extracts reveal two separate optima at pH 6.5 and 7.5. Native isoelectric focusing gels of sampies from etiolated tissue reveal a single band of PCR activity with a pl of 7.8.

Journal Article↗