Search PubMed⌕ Search

Biomedical subjects

C A Mitchell

Publications and source records attributed to C A Mitchell.

At least 91 records · Page 5Linked to original sources
PubMed1996

Varying plant density and harvest time to optimize cowpea leaf yield and nutrient content.

Plant density and harvest time were manipulated to optimize vegetative (foliar) productivity of cowpea [Vigna unguiculata (L.) Walp.] canopies for future dietary use in controlled ecological life-support systems as vegetables or salad greens. Productivity was measured as total shoot and edible dry weights (DW), edible yield rate [(EYR) grams DW per square meter per day], shoot harvest index [(SHI) grams DW per edible gram DW total shoot], and yield-efficiency rate [(YER) grams DW edible per square meter per day per grams DW nonedible]. Cowpeas were grown in a greenhouse for leaf-only harvest at 14, 28, 42, 56, 84, or 99 plants/m2 and were harvested 20, 30, 40, or 50 days after planting (DAP). Shoot and edible dry weights increased as plant density and time to harvest increased. A maximum of 1189 g shoot DW/m2 and 594 g edible DW/m2 were achieved at an estimated plant density of 85 plants/m2 and harvest 50 DAP. EYR also increased as plant density and time to harvest increased. An EYR of 11 g m-2 day-1 was predicted to occur at 86 plants/m2 and harvest 50 DAP. SHI and YER were not affected by plant density. However, the highest values of SHI (64%) and YER (1.3 g m-2 day-1 g-1) were attained when cowpeas were harvested 20 DAP. The average fat and ash contents [dry-weight basis (dwb)] of harvested leaves remained constant regardless of harvest time. Average protein content increased from 25% DW at 30 DAP to 45% DW at 50 DAP. Carbohydrate content declined from 50% DW at 30 DAP to 45% DW at 50 DAP. Total dietary fiber content (dwb) of the leaves increased from 19% to 26% as time to harvest increased from 20 to 50 days.

Biomass↗
PubMed1996

Introduction of a donor exposure reduction programme for multiple-transfused very-low-birth-weight infants.

OBJECTIVE: To conduct an audit of the frequency of red cell concentrate transfusions (RCCTs) in infants of different weight categories, the donor exposure rate (DER), in these transfused infants and the volume of blood wasted during each transfusion, and to identify from this baseline information specific categories of infants who would benefit from the introduction of a limited donor exposure programme (LDEP). STUDY SETTING: Neonatal wards and neonatal intensive care unit (NICU), Tygerberg Hospital, Western Cape. STUDY DESIGN: A prospective descriptive study and comparison with a historic control group. SUBJECTS: Information on the birth weight, age at the time of each RCCT and number of blood donors to whom an infant was exposed were collected post factum for all infants admitted to the neonatal wards and NICU between May 1993 and May 1994. During this time, the red blood cell concentrate was supplied as single paediatric bags (180 ml) transfused within 14 days of donation. An LDEP was introduced in February 1995. With this system, red blood cells were supplied as triple packs: a main unit of 250 ml with three empty satellite packs allowing up to three separate transfusions. These were assigned to a specific infant and were to be transfused within 21 days of donation. A second system where one adult blood bag was divided into two 180 ml bags and assigned to one infant to be transfused within 35 days of donation was also assessed. RESULTS: Of the 7854 infants admitted during the first 12-month audit period, 387 (4.9%) received 977 RCCTs. Of these, 183 (47.3%) received one transfusion, 72 (18.6%) two transfusions, 51 (13.2%) three transfusions, 27 (7.0%) four transfusions and 54 (13.9%) five or more transfusions. Infants (N = 188) with a birth weight below 1500 g admitted to the NICU were identified as the group with the highest prevalence of RCCTs (68.6%), and it was therefore decided that in the prospective study such infants would qualify for the LDEP. A total of 81 infants was transfused with either the double (N = 47) or the triple bags (N = 34) over a 5-month period. The decrease in the mean DER (+/-SD) was clinically significant when the triple (1.9 +/- 0.8) (P = 0.0001) and the double bags (1.6 +/- 0.8) (P = 0.0001) were compared with the previous single-bag system (4.4 +/- 3.5). Of concern was the large mean volume of concentrated red cells (118.5 +/- 12.5 ml) wasted per transfusion with the single-bag system. CONCLUSIONS: This survey confirmed a high RCCT rate as well as a very high DER in very-low-birth-weight (VLBW) infants treated at a tertiary centre. By assigning a triple or double bag of red cells from one blood donor and extending the storage of blood for small-volume RCCTs in infants from 14 days to 35 days, donor exposure was reduced significantly. We urge the introduction of the multibag blood transfusion system and extended storage period of blood for small-volume RCCT for VLBW infants in South Africa.

Adult↗
PubMed1995

An essential role for lysophosphatidylcholine in the inhibition of platelet aggregation by secretory phospholipase A2.

The release of secretory phospholipase A2 (sPLA2) into the mammalian circulation may contribute to the development of hemorrhagic and inflammatory diseases. sPLA2 has previously been shown to alter the behavior of platelets, leukocytes, and endothelial cells, although the molecular basis for these cellular effects has not been established. Our studies indicate that the inhibition of platelet aggregation by snake, bee venom, and pancreatic sPLA2 is dependent on a plasma cofactor. This cofactor resides within the lipoprotein fraction of plasma, with 54%, 31%, and 11% of the activity present in the high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very low density lipoprotein (VLDL) fractions, respectively. Delipidation of HDL and LDL was associated with the complete loss of platelet-inhibitory activity. Incubation of purified sPLA2 with the HDL fraction of plasma resulted in the time-dependent generation of lysophosphatidylcholine (lysoPC). The formation of lysoPC correlated with the inhibition of platelet aggregation. Purified lysoPC (10 to 100 micrograms/mL) inhibited platelet aggregation and dense granule release induced by thrombin (0.05 U/mL), collagen (1 micrograms/mL), ionophore A23187 (2 mumol/L), ADP (12.5 mumol/L), and adrenaline (3.2 mumol/L). The inhibition of platelet aggregation by lysoPC was dose-dependent and correlated with decreased fibrinogen binding to glycoprotein IIb-IIIa. Our studies indicate that the enzymatic generation of lysoPC from plasma lipoproteins is essential for the sPLA2-mediated inhibition of platelet activation in the presence of albumin. These results raise the possibility that the toxic effects of circulating sPLA2 may be due in part to the generation of the bioactive lysophospholipid, lysoPC.

Animals↗
PubMed1995

Tissue distribution and intracellular localisation of the 75-kDa inositol polyphosphate 5-phosphatase.

The 75-kDa inositol polyphosphate 5-phosphatase (75-kDa 5-phosphatase) hydrolyses several important mediators of intracellular calcium homeostasis, including inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. Northern analysis of various human tissues revealed the 75-kDa 5-phosphatase has a ubiquitous expression, where differential splicing may occur in specific tissues. Prominent expression of a 4.4-kb transcript was noted in human lung, thymus, testes and placenta, and a 4.6-kb transcript was observed in heart, brain, kidney, ovary and colon. Determination of the intracellular location of the enzyme by indirect immunofluorescence, demonstrated that the 75-kDa 5-phosphatase was associated with mitochondrial and cytosolic cellular compartments. Immunoprecipitation of the total cell homogenate of human lung carcinoma cells (A549) with anti-(recombinant 75-kDa 5-phosphatase) antibodies revealed that the 75-kDa 5-phosphatase is the major PtdIns(4,5)P2 5-phosphatase in this cell line. Analysis of PtdIns(4,5)P2 5-phosphatase activity in subcellular fractions of A549 cells revealed peak 75-kDa 5-phosphatase enzyme activity in the cytosolic and mitochondrial enriched fractions. Immunoblot analysis further confirmed the mitochondrial location of the enzyme. This study demonstrates the tissue distribution and intracellular location of the 75-kDa 5-phosphatase and reveals a novel location for an enzyme involved in phosphatidylinositol turnover.

Cell Line↗
PubMed1995

Association of an unusual form of a Pax7-like gene with increased efficiency of skeletal muscle regeneration.

Efficiency of regeneration of mechanically injured skeletal muscle is more pronounced in SJL/J mice, as compared to other laboratory strains in which regenerative properties of skeletal muscle are uniformly poor. Previously, we postulated that a small number of genes might differ between SJL/J and other mouse strains, and would be responsible for this variation in the efficiency of skeletal muscle regeneration. The results of initial experiments demonstrated that SJL/J mice have a unique form of the myogenic gene, Myo-D1, which partly influences efficiency of skeletal muscle repair, and that other genes were also involved. To identify other candidate genes, differences were sought within the myogenic paired box/homeobox-containing gene Pax7 between SJL/J and other laboratory mouse strains. Southern blotting indicated that SJL/J, Quackenbush and DDO mice share a Pax7/TaqI RFLP which differs from all other laboratory strains tested. This RFLP is most likely due to sequence differences within the homeobox of a Pax7-like gene. In vivo studies revealed that Quackenbush and DDO mice also share the same regenerative properties of mechanically damaged skeletal muscle as SJL/J mice. Since Quackenbush and DDO mice lack the SJL/J type of Myo-D1, and DDO belong to a different mouse sub-species, these studies suggest that structural alterations in the homeobox of a Pax7-like gene may be implicated in the effectiveness of renewal of damaged skeletal muscle of the limb in the mature animal.

Animals↗
PubMed1995

Phosphatidylinositol 3,4,5-trisphosphate is a substrate for the 75 kDa inositol polyphosphate 5-phosphatase and a novel 5-phosphatase which forms a complex with the p85/p110 form of phosphoinositide 3-kinase.

Agonist-stimulated production of phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3], is considered the primary output signal of activated phosphoinositide (PI) 3-kinase. The physiological targets of this novel phospholipid and the identity of enzymes involved in its metabolism have not yet been established. We report here the identification of two enzymes which hydrolyze the 5-position phosphate of PtdIns(3,4,5)P3, forming phosphatidylinositol (3,4)-bisphosphate. One of these enzymes is the 75 kDa inositol polyphosphate 5-phosphatase (75 kDa 5-phosphatase), which has previously been demonstrated to metabolize inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. We have identified a second PtdIns(3,4,5)P3 5-phosphatase in the cytosolic fraction of platelets, which forms a complex with the p85/p110 form of PI 3-kinase. This enzyme is immunologically and chromatographically distinct from the platelet 43 kDa and 75 kDa 5-phosphatases and is unique in that it removes the 5-position phosphate from PtdIns(3,4,5)P3, but does not metabolize PtdIns(4,5)P2, Ins(1,4,5)P3 or Ins(1,3,4,5)P4. These studies demonstrate the existence of multiple PtdIns(3,4,5)P3 5-phosphatases within the cell.

Amino Acid Sequence↗
PubMed1995

Immunohistochemical localization of thrombomodulin in normal human skin and skin tumours.

Thrombomodulin (TM) expression has been investigated in sections of normal human skin, in cultured normal human keratinocytes, and in a variety of skin tumours. TM was present in squamous epithelial cells in the spinous layer of normal epidermis and in the outer root sheath of hair follicles, but was absent in the cells of the basal layer. It appeared to be predominantly localized to the cell membrane and the intercellular bridges in these areas. Cultured normal human keratinocytes demonstrated functionally active constitutive TM expression on their cell surface. Immunoperoxidase staining of skin tumours using anti-human TM antibodies demonstrated a typical cell membrane positivity in tumours with squamous or hair follicle differentiation. Basal cell carcinomas showed TM expression only in areas where incomplete squamoid metaplasia occurred. Sweat gland tumours and lesions of the melanogenic system failed to express TM. The localization of TM by immunostaining in various benign and malignant skin tumours typically correlated with their normal skin element of origin. The physiological significance of TM expression in the epidermis is currently undefined.

Basal Cell Carcinoma↗
PubMed1995

The genotype of bone marrow-derived inflammatory cells does not account for differences in skeletal muscle regeneration between SJL/J and BALB/c mice.

This study determined whether the genotype of bone marrow-derived inflammatory cells contributes to the more pronounced leukocytic exudation and extensive new muscle formation seen in SJL/J compared with BALB/c mice after a crush-injury (Mitchell et al. 1992). Female SJL/J mice were whole-body irradiated and reconstituted with male bone marrow from the BALB/c strain, and irradiated BALB/c females reconstituted with male SJL/J bone marrow. The mice were allowed to recover for 3 weeks and the tibialis anterior muscle (in a leg which had been protected from irradiation) was injured by crushing. At 3 and 10 days after injury the extent of necrotic debris, mononuclear leukocytic infiltration and new muscle formation was assessed in the muscles. The SJL/J mice reconstituted with BALB/c bone marrow showed extensive mononuclear leukocytic infiltration and clearance of necrotic debris when compared with BALB/c mice reconstituted with SJL/J bone marrow, and these strain-specific differences mirrored those seen with control bone marrow reconstituted hosts and non-irradiated hosts. The results show that the genotype of the bone marrow-derived macrophages is not responsible for the superior regeneration of crush-injured skeletal muscle in SJL/J mice, and it appears that factors intrinsic to the muscle tissue may be of central importance.

Animals↗
PubMed1995

Probability of failure of orthodontic brackets bonded with different cementing agents.

OBJECTIVES: The aim of this study was to compare the maximum loads at failure and the probability of failure of three glass ionomer cements and a composite cement bonding orthodontic brackets to human premolar teeth. METHODS: The cements studied included a conventional glass ionomer cement, two resin-modified glass ionomer cements and a composite cement. The roots of 200 human premolar teeth were embedded in acrylic resin and the buccal enamel surface of the crown prepared as required. Each cement used to bond the bracket to the enamel was weighted, and light-cured where required. The specimens were stored for 10 min or 24 h at 37 degrees C and 100% humidity. A tensile shear force was applied via a wire loop placed under the wings of the bracket. The maximum load at failure was noted and subjected to Weibull analysis to compare probabilities of survival for each cement. The data obtained was also analyzed using a Kruskal-Wallis test followed by comparison of the groups using Mann-Whitney tests. RESULTS: Comparison of the loads at failure revealed that the composite cement was significantly stronger than the glass ionomer cements at 10 min and 24 h (p<0.05). Weibull analysis of the results gave values for the Weibull moduli and probabilities of survival for an orthodontic bracket under a given load for each cement at 10 min and 24 h. SIGNIFICANCE: . Glass ionomer cements give a number of clinically significant advantages over composite cement in the retention of brackets. The resin-modified glass ionomer cements tested had a higher probability of survival than the conventional cement tested at 24 h. However, further improvements in their early bond strength would be clinically beneficial.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1995

Factors influencing the failure of dental glass ionomer luting cement due to contraction.

Glass ionomer cement used to fix a post within the root of a tooth undergoes cohesive failure on setting. This study aimed to determine the importance of humidity, substrate material and post design on cement failure. Nine groups of five specimens were prepared: groups 1-3 addressed the influence of post design and sectioning process on cement failure, while groups 4-9 examined the interaction between the cement, substrates and humidity. Replicas were prepared of all specimens and viewed using scanning electron microscopy. It was concluded that humidity and substrate influenced the failure of glass ionomer cement whereas post design did not.

Animals↗
PubMed1995

Asthma management and mode of acquisition of inhaled bronchodilators.

BACKGROUND: Controversy has existed about the benefits and disadvantages associated with the availability of inhaled bronchodilators over the counter (OTC). AIMS: To compare sociodemographic features, use of preventive medications, use of medical services and control of asthma in adults who purchased inhaled bronchodilators OTC with those who purchased on prescription (script). METHODS: A cross-sectional telephone survey of 772 adults 18 years and over who used inhaled bronchodilators for their asthma. Symptoms, asthma medications, and management practices were determined by a structured questionnaire administered by trained telephone interviewers. RESULTS: Two hundred and thirty adults purchased their bronchodilator OTC and 542 on script. OTC purchasers were more likely to be male (OR: 1.5), have had tertiary education (1.5) and be in paid employment (2.8); they were less likely to report frequent symptoms (wheeze, nocturnal symptoms or EIA more than once a week) (0.71); were less likely to use preventive medications more than twice a day (0.57) and were less likely to have consulted a general practitioner in the previous year (0.38). However, poor control of asthma symptoms was evident in both OTC and script groups. Forty per cent of the OTC group who had symptoms more than two to three times a week and 34% of the script group were not using preventive medication. CONCLUSIONS: Undertreatment and suboptimal management of asthma were apparent in both OTC and script groups.

Adult↗
PubMed1995

Measuring the systemic effects of inhaled beclomethasone: timed morning urine collections compared with 24 hour specimens.

BACKGROUND: Inhaled glucocorticoid therapy has systemic effects including hypothalamic-pituitary-adrenal (HPA) suppression. The optimal test for detecting these effects has not been defined. METHODS: Timed urine collections and 09.00 hour plasma cortisol levels were obtained from 12 normal volunteers receiving inhaled placebo, beclomethasone (BDP) 800 or 2000 micrograms/day. The 24 hour urine samples were collected as follows: first hour after waking (hour 1), the next two hours after waking (hours 2 and 3), remainder of day, and overnight, with results expressed as urine cortisol/creatinine (UCC) ratios and as hourly cortisol output in the timed collections. Twenty four hour urinary cortisol excretion was also calculated. Medication was blinded and given in random order with a washout period of at least 11 days between each treatment arm. RESULTS: None of the UCC ratios changed with BDP 800 micrograms/day. UCC ratios at hour 1, hour 2 and 3, and overnight, and 24 hour urinary free cortisol excretion were reduced after BDP 2000 micrograms/day, whilst remainder of day UCC ratio and the plasma cortisol level did not change significantly. Cortisol output showed similar changes. In a follow up study BDP 1400 micrograms/day also reduced UCC ratios for the first two hours after waking. CONCLUSIONS: UCC ratios are as sensitive as the more cumbersome 24 hour urinary free cortisol excretion, and more sensitive than single morning plasma cortisol measurements, in detecting the effects of inhaled beclomethasone on the HPA axis.

Administration, Inhalation↗
PubMed1995

Mass versus activity: validation of an immunometric assay for bone alkaline phosphatase in serum.

A detailed investigation of the performance of an immunometric assay for the quantitation of bone alkaline phosphatase (ALP) in serum showed that precision of this assay was similar to that of lectin precipitation and electrophoretic methods. Relationships for mass and activity measurements of the bone isoform using samples from children and patients with Paget's disease were similar for lectin and electrophoretic methods. Purified liver enzyme showed 100% cross reactivity in the immunometric assay. However, comparison of the slopes between bone ALP mass and total ALP activity using only samples with predominantly liver or bone isoforms showed that the cross reactivity of the liver isoform in serum was 18.3%. Experiments in which increasing amounts of a sample containing 90% of liver isoform adding to a serum sample from a patient with Paget's disease showed a cross reactivity of 16.5%. The reference range for bone ALP mass was 7-28 micrograms/L for men (n = 77) and 5-20 micrograms/L for women (n = 110) in the age group 20-50 years. In women over 50 years bone ALP was 28% higher. Increased bone ALP mass was also demonstrated in patients with Paget's disease (n = 59), liver disease (n = 95), chronic renal failure (n = 41) and hyperthyroidism (n = 17).

Adolescent↗
PubMed1995

Effects of carbon dioxide level and plant density on cowpea canopy productivity for a bioregenerative life support system.

Plant density and atmospheric carbon dioxide level were manipulated to optimize productivity of cowpea [Vigna unguiculata (L.) Walp] for future use in a space-deployed Controlled Ecological Life Support System. Cowpea breeding line IT87D-941-1 was grown at plant densities of 3.6, 7.2, 10.7, or 14.3 plants m-2 in a growth chamber maintained at 400 (control) or 1200 (elevated) micromoles CO2 mol-1. Both green leaves and dried seeds were harvested as edible yield. Crop productivity was measured by edible yield rate (EYR), harvest index (HI), yield efficiency rate (YER), energy efficiency, and net photosynthesis (Pn). Increasing plant density within a canopy tended to increase EYR, but decreased HI and YER. Elevated CO2 also increased EYR, but decreased HI and YER as well. However, when the energy penalty for crop production was taken into consideration, cowpea crops grown under elevated CO2 were more productive than those grown at control CO2. Pn averaged 15 micromoles CO2 m-2 s-1 for cowpeas grown at 400 micromoles CO2 mol-1. Low Pn at the beginning and end of the cropping cycle indicated waste of high irradiance lighting during those times.

Agriculture↗
PubMed1994

Evidence for adenine methylation within the mouse myogenic gene Myo-D1.

Previous studies have indicated that there may be uncleavable TaqI sites (TCGA) within the mouse myogenic gene, Myo-D1. Fragments of DNA bearing most of the presumed insensitive TaqI sites have been reproduced using PCR. The presence of each of the originally uncleavable TaqI sites has been confirmed and each TaqI site has been shown to be sensitive to TaqI hydrolysis in PCR-synthesized genomic DNA. Since TaqI is inhibited by methylation of the adenine residue within its recognition sequence (but not by cytosine methylation), it is suggested that specific adenine bases are methylated in the coding region of Myo-DI and maintained throughout cell division. The same TaqI recognition sequences are insensitive to digestion in genomic DNA isolated from various mouse tissues including fetus, regenerating skeletal muscle and a myogenic cell line, all of which express Myo-D1. Thus, adenine methylation is not a modification of DNA following gametic fusion nor does it appear to play a major role in regulation of Myo-D1 expression.

Adenine↗
PubMed1994

Tyrosine kinases regulate the cytoskeletal attachment of integrin alpha IIb beta 3 (platelet glycoprotein IIb/IIIa) and the cellular retraction of fibrin polymers.

Integrins promote cell-substratum and cell-cell adhesion by acting as transmembrane linker molecules between extracellular adhesion proteins and the actin-rich cytoskeleton. The integrin alpha IIb beta 3 (platelet glycoprotein IIb/IIIa) is essential for platelet spreading, aggregation, fibrin clot retraction, and for the transduction of extracellular signals. We examined the effect of the specific tyrosine kinase inhibitor herbimycin A on integrin and cytoskeletal-mediated events in thrombin-stimulated platelets. Incubation of washed platelets for 24 h with herbimycin A (5 microM) abolished the thrombin-stimulated cytoskeletal enzyme activity of pp60c-src in parallel with a reduction in the tyrosine phosphorylation of multiple platelet proteins, as assessed with anti-phosphotyrosine immunoblots. However, thrombin-induced activation of protein kinase C and the production of thromboxane A2 were not altered by herbimycin A. Despite the absence of cytoskeletal pp60c-src enzyme activity, platelet shape change, aggregation, and serotonin release were unaltered following platelet stimulation with thrombin (0.05-1.0 unit/ml). Herbimycin A-treated platelets also demonstrated normal platelet aggregation in response to collagen (5 micrograms/ml), ionophore A23187 (2 microM), and ADP/adrenaline (10 microM each). However, the ability of herbimycin A-treated platelets to retract fibrin gels was significantly reduced. This defect in clot retraction was associated with reduced incorporation of integrin alpha IIb beta 3 into the cytoskeletal fraction of thrombin-aggregated platelets. Our studies suggest that tyrosine kinases in platelets regulate the cytoskeletal attachment of alpha IIb beta 3, as an essential process for the transmission of cellular contractile forces to fibrin polymers.

Benzoquinones↗