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Biomedical subjects

C A Mitchell

Publications and source records attributed to C A Mitchell.

At least 73 records · Page 4Linked to original sources
PubMed1997

Dynamic optimization of CELSS crop photosynthetic rate by computer-assisted feedback control.

A procedure for dynamic optimization of net photosynthetic rate (Pn) for crop production in Controlled Ecological Life-Support Systems (CELSS) was developed using leaf lettuce as a model crop. Canopy Pn was measured in real time and fed back for environmental control. Setpoints of photosynthetic photon flux (PPF) and CO2 concentration for each hour of the crop-growth cycle were decided by computer to reach a targeted Pn each day. Decision making was based on empirical mathematical models combined with rule sets developed from recent experimental data. Comparisons showed that dynamic control resulted in better yield per unit energy input to the growth system than did static control. With comparable productivity parameters and potential for significant energy savings, dynamic control strategies will contribute greatly to the sustainability of space-deployed CELSS.

Air Conditioning↗
PubMed1997

Environmental modification of yield and nutrient composition of 'Waldmann's Green' leaf lettuce.

Leaf number, dry weight, and nutrient composition of Lactuca sativa L. cv. Waldmann's Green leaves were compared following 9 days of treatment in a controlled environment room under various combinations of photosynthetic photon flux (PPF:350 vs 800 micromoles m-2 s-1), atmospheric CO2 level (ambient vs 1500 micromoles mol-1), and single-strength (1X:15 mM) vs double-strength (2X:30 mM) nitrogen (N) as NO3- alone or as NH4(+) + NO3- (1:5 molar ratio). CO2 enrichment greatly enhanced leaf number under all PPF and N conditions, but increased leaf dry weight only at high PPF. Conditions favoring high photosynthesis enhanced leaf starch content 3-fold, and protein content increased as much as 64% with 2X NH4(+)+NO3-. Free sugar content was 6 to 9% of leaf dry weight for all treatment combinations, while fat was 1.5 to 3.5%. Ash content varied from 15 to 20% of leaf dry weight. Modified controlled environments can be used to enhance the nutritional content as well as the yield of crops to be used for life support in space-deployed, self-sustaining human habitats. Leaf lettuce is a useful model crop for demonstrating the potential of nutritional value added by environmental manipulation.

Biomass↗
PubMed1997

In vitro assessment of the biological activity of basic fibroblast growth factor released from various polymers and biomatrices.

The kinetics of controlled release of basic fibroblast growth factor (bFGF) from polymers (sutures, polycarbonate, Hydron, and Elvax), biopolymers (alginate), and biomatrices (lens capsules), and conditions for storage of bFGF (temperature, plastic type, heparin) were evaluated in vitro. Tissue culture proliferation bioassays with 3T3 fibroblasts, showed that only lens capsules with bFGF had a sustained release of bFGF for up to three weeks. The other materials released all of the 'bound' bFGF with two hours or produced an inflammatory response in vivo. Therefore, the lens tissue had the most potential for controlled long-term delivery of bFGF in vivo. These studies emphasise the importance of in vitro analysis of release kinetics of growth factors from a range of materials as a basis for potential in vivo applications.

3T3 Cells↗
PubMed1996

Underexpression of the 43 kDa inositol polyphosphate 5-phosphatase is associated with cellular transformation.

The 43 kDa inositol polyphosphate 5-phosphatase (5-phosphatase) hydrolyses the second messenger molecules inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4]. We have underexpressed the 43 kDa 5-phosphatase by stably transfecting normal rat kidney cells with the cDNA encoding the enzyme, cloned in the antisense orientation into the tetracycline-inducible expression vector pUHD10-3. Antisense-transfected cells demonstrated a 45% reduction in Ins(1,4,5)P3 5-phosphatase activity in the total cell homogenate upon withdrawal of tetracycline, and an approximately 80% reduction in the detergent-soluble membrane fraction of the cell, as compared with antisense-transfected cells in the presence of tetracycline. Unstimulated antisense-transfected cells showed a concomitant 2-fold increase in Ins(1,4,5)P3 and 4-fold increase in Ins(1,3,4,5)P4 levels. The basal intracellular calcium concentration of antisense-transfected cells (170 +/- 25 nM) was increased 1.9-fold, compared with cells transfected with vector alone (90 +/- 25 nM). Cells underexpressing the 43 kDa 5-phosphatase demonstrated a transformed phenotype. Antisense-transfected cells grew at a 1.7-fold faster rate, reached confluence at higher density and demonstrated increased [3H]thymidine incorporation compared with cells transfected with vector alone. Furthermore, antisense-transfected cells formed colonies in soft agar and tumours in nude mice. These studies support the contention that a decrease in Ins(1,4,5)P3 5-phosphatase activity is associated with cellular transformation.

3T3 Cells↗
PubMed1996

Focal adhesion kinase (pp125FAK) cleavage and regulation by calpain.

Focal adhesion kinase (125 kDa form; pp125FAK) is a widely expressed non-receptor tyrosine kinase that is implicated in integrin-mediated signal transduction. We have identified a novel means of pp 125FAK regulation in human platelets, in which this kinase undergoes sequential proteolytic modification from the native 125 kDa form to 90, 45 and 40 kDa fragments in thrombin-, collagen- and ionophore A23187-stimulated platelets. The proteolysis of pp125FAK was prevented by pretreating platelets with the calpain inhibitors calpeptin or calpain inhibitor-1, and was reproduced in vitro by incubating immunoprecipitated pp125FAK with purified calpain. Proteolysis of pp125FAK resulted in a dramatic reduction in its autokinase activity and led to its dissociation from the cytoskeletal fraction of platelets. These studies define a novel signal-terminating role for calpain, wherein proteolytic modification of pp125FAK attenuates its autokinase activity and induces its subcellular relocation within the cell.

Blood Platelets↗
PubMed1996

Asthma management in eastern Australia, 1990 and 1993.

OBJECTIVE: To compare the prevalence and management of asthma before and after institution of the National Asthma Campaign. DESIGN: Repeat population-based cross-sectional analytic surveys. SETTING: Eastern Australia (Sydney, Brisbane, Melbourne, and the Hunter Valley, New South Wales) in September 1990 and 1993. SUBJECTS: Primary school children and their parents from 33 schools (8746 children) in 1990 and 40 schools (10 106 children) in 1993. OUTCOME MEASURES: Frequency of respiratory symptoms; diagnoses of asthma; medications; lung function measurements; possession of a peak flow meter and a written action plan. RESULTS: Age and sex distribution of the subjects and the reported prevalence of asthma were similar in 1990 and 1993. The frequency of reported episodes of wheezing and troublesome cough increased significantly in children between 1990 and 1993. Asthma management improved in accordance with current recommendations, with significantly decreased use of regular inhaled bronchodilator medication in children and increased use of preventive medication, monitoring of lung function by doctors and use of peak flow meters and written action plans in both children and adults. CONCLUSION: There is evidence that the National Asthma Campaign may have contributed to increased awareness and improved management of asthma in children and adults in eastern Australia.

Adult↗
PubMed1996

Excess nutrients in hydroponic solutions alter nutrient content of rice, wheat, and potato.

Environment has significant effects on the nutrient content of field-grown crop plants. Little is known, however, about compositional changes caused by controlled environments in which plants receive only artificial radiation and soilless, hydroponic culture. This knowledge is essential for developing a safe, nutritious diet in a Controlled Ecological Life-Support System (CELSS). Three crops that are candidates for inclusion in a CELSS (rice, wheat, and white potato) were grown both in the field and in controlled environments where the hydroponic nutrient solution, photosynthetic photon flux (PPF), and CO2 level were manipulated to achieve rapid growth rates. Plants were harvested at maturity, separated into discrete parts, and dried prior to analysis. Plant materials were analyzed for proximate composition (protein, fat, ash, and carbohydrate), total nitrogen (N), nitrate, minerals, and amino-acid composition. The effect of environment on nutrient content varied by crop and plant part. Total N and nonprotein N (NPN) contents of plant biomass generally increased under controlled-environment conditions compared to field conditions, especially for leafy plant parts and roots. Nitrate levels were increased in hydroponically-grown vegetative tissues, but nitrate was excluded from grains and tubers. Mineral content changes in plant tissue included increased phosphorus and decreased levels of certain micronutrient elements under controlled-environment conditions. These findings suggest that cultivar selection, genetic manipulation, and environmental control could be important to obtain highly nutritious biomass in a CELSS.

Amino Acids↗
PubMed1996

Thermographic assessment of dentine pin placement.

OBJECTIVE: This in-vitro study aimed to examine the change in surface temperature induced by the actions of drills for the placement of dentine pins. METHODS: Ten decoronated extracted premolar teeth were embedded by the apical tip of their roots in orthoresin. They were held in a bench vice and allowed to reach the ambient temperature of 24 degrees C. A thermal imaging camera, Agema Thermovision 900 series, was positioned 0.05 m perpendicular to the decoronated surface. Sequential recording of a series of images was stored at a rate of three per second during each stage of the pin placement procedure. This included a pilot drill, a channel cutting drill and the pin placement. All pins were 0.675 mm diameter x 2 mm in length and were placed 1 mm from the amelo-dentinal junction using a Kavo handpiece rotating at 4000 rpm. RESULTS: The mean baseline temperature for the thermally stabilized teeth was 23.9 degrees C. The action of the round pilot drill changed the temperature from baseline by 25 degrees C. The action of the channel drill generated the greatest heat, with a mean maximum temperature recorded during these procedures of 94 degrees C +/- 9 degrees C. The pilot drill produced a mean change from baseline of 31.3 degrees C +/- 17.7 degrees C during pin placement. CONCLUSIONS: The placement of dentine pins produced a high temperature increase on the surface of the dentine. All stages of pin placement gave rise to an increased temperature, but this was maximal with the channel drill. Further studies are required to determine whether these surfaces temperatures are transferred to the pulpal chamber.

Body Temperature↗
PubMed1996

Regulation of second messengers by the inositol polyphosphate 5-phosphatases.

The inositol polyphosphate 5-phosphatases are an enlarging family of enzymes that terminate the signals generated by the phosphoinositide kinases and phospholipase C. Given the diverse signalling functions of both the polyphosphoinositides and Ins(1,4,5)P3, it is predicted that the 5-phosphatases will play a critical role in regulating many cellular events, in particular membrane trafficking and cell growth.

Amino Acid Sequence↗
PubMed1996

Altered thrombomodulin staining in blistering dermatoses.

The immunocytochemical distribution of thrombomodulin (TM) was examined in sections of skin from patients with blistering dermatoses occurring in the presence and absence of acantholysis. Skin sections were stained using polyclonal and monoclonal anti-human TM antibodies and were correlated with the staining pattern that resulted when using the monoclonal antibody 32-2B, which recognises the chief desmosomal adhesion molecule desmoglein I (DG I). Our study demonstrates a loss of TM staining in acantholytic dermatoses, occurring only in the region of actual disruption of the intercellular bridging between keratinocytes in the stratum spinosum. The thrombomodulin antigen expression paralleled the DG I expression. The strong correlation between the DG I and TM immunostaining pattern in both normal skin and acantholytic dermatoses supports the concept that TM has a role in mediating adhesion processes between keratinocytes.

Acantholysis↗
PubMed1996

The evaluation of post-retained crowns using a custom-designed fatigue machine.

There are many published reports of static tests on dental materials that are required to perform clinically under a range of load amplitudes and cyclic frequencies. There are fewer reports in the dental literature of fatigue tests on dental structures and materials, and these are reviewed in this paper along with a description of the design, manufacture and commissioning of a machine which can apply chosen cyclic load/time characteristics up to a maximum amplitude of 700 N and frequency of 5 Hz. The machine design is not specific to particular test specimens but is widely applicable within dental materials testing. The machine is being used for a continuing study of post-retained crowns, cemented with glass-ionomer cement. The planning of fatigue tests and the interpretation of results is discussed with reference to the experience of previous authors, and it is concluded that a survival analysis approach offers a means of understanding materials' performances. The initial results from a random, blocked comparison of three glass-ionomer luting cements indicated that cyclic loads can be identified to give a 50% survival probability for specimens. It is expected that loads experienced in vivo have lower amplitude than those applied in this study, however, such loading cycles have been chosen to facilitate material comparisons. It is concluded that gaining significant results under laboratory fatigue conditions is difficult, but that they may usefully complement clinical trials.

Animals↗
PubMed1996

Adenoid cystic carcinoma of the left main bronchus mimicking MacLeod's syndrome.

A 15 year old girl who was labelled as having MacLeod's syndrome on the basis of a chest radiograph was subsequently, at the age of 23 years, found to have an adenoid cystic carcinoma obstructing the left main bronchus. This case emphasises the need to exclude a central lesion in cases of unilateral hyperlucent lung.

Adult↗
PubMed1996

Enhancement of neovascularization in regenerating skeletal muscle by the sustained release of erucamide from a polymer matrix.

The angiogenic agent erucamide (cis-13-docosenamide), incorporated into a polymeric biomaterial (Elvax 40P, a copolymer of ethylene and vinyl acetate), was used to determine whether angiogenesis can be increased in the regenerating skeletal muscle, and whether the enhanced revascularization improves the new muscle formation. The angiogenic nature of this lipid was confirmed in a rat cornea-micropocket assay, prior to insertion of small strips of the polymer containing either 3 micrograms, 300 micrograms erucamide or only polymer as a control into the mid-region of crush-injured tibialis anterior (TA) muscles of forty-five adult male BALB/c mice. All TA muscles were sampled ten days after injury and analyzed morphometrically. Statistical analyses of the mean blood vessel area density in lesions from twelve perfused TA muscles (three from each of the erucamide-treated or control group), revealed a dose-dependent angiogenic effect of erucamide: a dosage of 3 micrograms increased mean blood vessel area density to 5.1% compared to 2.0% in controls, due to numerous large caliber, thin-walled vessels, whereas the mean vessel area density in both the 30-micrograms (3.5%) and 300-micrograms (1.5%) doses were similar to controls. However, at all three doses tested, erucamide did not significantly alter the degree of new muscle formation, connective tissue deposition, or removal of necrotic debris.

Animals↗
PubMed1996

Dynamic control of photosynthetic photon flux for lettuce production in CELSS.

A new dynamic control of photosynthetic photon flux (PPF) was tested using lettuce canopies growing in the Minitron II plant-growth/canopy gas-exchange system. Canopy photosynthetic rates (Pn) were measured in real time and fedback for further environment control. Pn can be manipulated by changing PPF, which is a good environmental parameter for dynamic control of crop production in a Controlled Ecological Life-Support Systems CELSS. Decision making that combines empirical mathematical models with rule sets developed from recent experimental data was tested. With comparable yield indices and potential for energy savings, dynamic control strategies will contribute greatly to the sustainability of space-deployed CELSS.

Biomass↗
PubMed1996

The exogenous administration of basic fibroblast growth factor to regenerating skeletal muscle in mice does not enhance the process of regeneration.

The effects, in vivo, of the exogenous administration of bFGF on myogenesis of regenerating skeletal muscle was assessed either morphometrically or autoradiographically in three separate models of muscle injury in mice: crush-injured, denervated, and dystrophic (mdx) muscles. The bFGF was administered at various doses and different time schedules, sometimes in combination with heparin, into injured tibialis anterior muscles of mice. Delivery of the bFGF was either by direct intramuscular injection or by the sustained release from 888polymers (Hydron or Elvax) implanted into the muscles. The bioactivity of bFGF was confirmed in vitro by measuring its ability to stimulate the proliferation of BALB/c-3T3 fibroblasts and muscle precursor cell lines. The ability of bFGF to stimulate angiogenesis in vivo was confirmed by the implantation of controlled-release polymers containing bFGF into the normally avascular cornea of rats. No measurable effect of bFGF was seen in any of the models of skeletal muscle injury under these experimental conditions, indicating that the availability of biologically active bFGF is not a limiting factor in the regeneration of skeletal muscle following injury.

Animals↗
PubMed1996

Identifying yield-optimizing environments for two cowpea breeding lines by manipulating photoperiod and harvest scenario.

Photoperiod and harvest scenario of cowpea (Vigna unguiculata L. Walp) canopies were manipulated to optimize productivity for use in future controlled ecological life-support systems. Productivity was measured by edible yield rate (EYR:g m-2 day-1), shoot harvest index (SHI: g edible biomass [g total shoot dry weight]), and yield-efficiency rate (YER:g edible biomass m-2 day-1 per[g nonedible shoot dry weight]). Breeding lines 'IT84S-2246' (S-2246) and "IT82D-889' (D-889) were grown in a greenhouse under 8-, 12-, or 24-h photoperiods. S-2246 was short-day and D-889 was day-neutral for flowering. Under each photoperiod, cowpeas were harvested either for leaves only, seeds only, or leaves plus seeds (mixed harvest). Photoperiod did not affect EYR of either breeding line for any harvest scenario tested. Averaged over both breeding lines, seed harvest gave the highest EYR at 6.7 g m-2 day-1. The highest SHI (65%) and YER (94 mg m-2 day-1 g-1) were achieved for leaf-only harvest of D-889 under an 8-h photoperiod. For leaf-only harvest of S-2246, both SHI and YER increased with increasing photoperiod, but declined for seed-only and mixed harvests. However, photoperiod had no effect on SHI or YER for D-889 for any harvest scenario. A second experiment utilized the short-day cowpea breeding line 'IT89KD-288' (D-288) and the day-neutral breeding line 'IT87D-941-1' (D-941) to compare yield parameters using photoperiod extension under differing lamp types. This experiment confirmed the photoperiod responses of D-889 and S-2246 to a mixed-harvest scenario and indicated that daylength extension with higher irradiance from high pressure sodium lamps further suppressed EYR, SHI, and YER of the short-day breeding line D-288.

Agriculture↗