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Biomedical subjects

C A Mitchell

Publications and source records attributed to C A Mitchell.

At least 181 records · Page 10Linked to original sources
PubMed1987

Stimulating productivity of hydroponic lettuce in controlled environments with triacontanol.

Triacontanol (1-triacontanol) applied as a foliar spray at 10(-7) M to 4-day-old, hydroponically grown leaf lettuce (Lactuca sativa L.) seedlings in a controlled environment increased leaf fresh and dry weight 13% to 20% and root fresh and dry weight 13% to 24% 6 days after application, relative to plants sprayed with water. When applied at 8 as well as 4 days after seeding, triacontanol increased plant fresh and dry weight, leaf area, and mean relative growth rate 12% to 37%. There was no benefit of repeating application of triacontanol in terms of leaf dry weight gain.

Biomass↗
PubMed1987

High dose intravenous gammaglobulin in immune haematological disease.

High dose intravenous gammaglobulin (0.4 g/kg/day) for five days, causes a rapid rise in the platelet count in immune thrombocytopenic purpura (ITP). The response in chronic ITP is transient making it useful in emergency situations. Efficacy in immune mediated neutropenia and warm antibody haemolytic anaemia has been reported but in limited numbers. We have used this therapy in twenty-three adults with ITP, one patient with immune neutropenia, four patients with warm antibody autoimmune haemolytic anaemia and one case of thrombotic thrombocytopenic purpura (TTP). In ITP only four of the twenty patients failed to respond to gammaglobulin and of these, three had a positive antinuclear factor but no other signs of systemic lupus erythematosis. The sole patient with neutropenia treated with IgG failed to show any response. In three patients with haemolytic anaemia parameters of haemolysis improved during therapy. The patient with TTP suffered a cerebrovascular accident during therapy prior to a documented response. High dose intravenous immunoglobulin rapidly elevates the platelet count in acute and chronic ITP. Its use in other immune mediated haematological conditions has yet to be fully evaluated.

Acute Disease↗
PubMed1987

Nebulized fenoterol and i.v. aminophylline in acute severe asthma.

We investigated the bronchodilator effect of intravenous aminophylline given after a cumulative dose of nebulized fenoterol of 2.4 mg in 18 patients with acute severe asthma. The mean forced expiratory volume in 1 s (FEV1) +/- SD before treatment was 0.72 +/- 0.22 l. The mean improvement in FEV1 after fenoterol was 0.64 +/- 0.39 l (85% of total improvement) and after aminophylline 0.11 +/- 0.13 l (15% of total improvement). The improvement after aminophylline was statistically significant (p less than 0.01), though quantitatively small. Thirteen patients improved after aminophylline by less than 0.15 l, and in only five was the improvement 0.2-0.4 l. There was no significant change in heart rate and subjective tremor score with treatment, although observed tremor (0 = absent, 4 = maximum) increased from 0.4 +/- 0.6 to 1.3 +/- 1.0 after all treatment. For the majority of patients presenting with acute severe asthma, it is likely that high doses of nebulized beta-2 agonist alone will produce near maximal bronchodilation in the short term.

Acute Disease↗
PubMed1986

Control of thrombin mediated cleavage of protein S.

Thrombin has been shown to cleave the vitamin K dependent cofactor protein S with subsequent loss of its cofactor activity. This study examines the control mechanisms for thrombin cleavage of protein S. The anticoagulant activity of activated protein C (APC) is enhanced fourteen fold by the addition of protein S. Thrombin cleaved protein S is seven fold less efficient than the native protein, and this loss of activity is due to reduced affinity of cleaved protein S for APC or the lipid surface compared to the intact protein. In the absence of Ca++, protein S is very sensitive to minimal concentrations of thrombin. As little as 1.5 nM thrombin results in complete cleavage of 20 nM protein S in 10 min and loss of cofactor activity. Ca++, in concentrations greater than 0.5 mM, will inhibit this cleavage and in the presence of physiological Ca++ concentrations, no cleavage of protein S could be demonstrated in spite of high concentrations of thrombin (up to 1 microM) and prolonged incubations (up to two hours). The endothelial surface protein thrombomodulin is very efficient in inhibiting the cleavage of protein S by thrombin suggesting that any thrombin formed on the endothelial cell surface is unlikely to cleave protein S, thus allowing the intact protein to act as a cofactor to APC. We conclude that the inhibitory effects of Ca++ and thrombomodulin on thrombin mediated cleavage of protein S imply that this event, by itself, is unlikely to represent a physiological control of the activity of protein S.

Calcium↗
PubMed1986

Growth reponses of eggplant and soybean seedlings to mechanical stress in greenhouse and outdoor environments.

Eggplant (Solanum melongena L. var. esculentum 'Burpee's Black Beauty') and soybean [Glycine max (L.) Merr. 'Wells II'] seedlings were assigned to a greenhouse or a windless or windy outdoor environment. Plants within each environment received either periodic seismic (shaking) or thigmic (flexing or rubbing) treatment, or were left undisturbed. Productivity (dry weight) and dimensional (leaf area and stem length) growth parameters generally were reduced more by mechanical stress in the greenhouse (soybean) or outdoor-windless environment (eggplant) than in the outdoor windy environment. Outdoor exposure enhanced both stem and leaf specific weights, whereas mechanical stress enhanced only leaf specific weight. Although both forms of controlled mechanical stress tended to reduce node and internode diameters of soybean, outdoor exposure increased stem diameter.

Environment↗
PubMed1985

Influence of seismic stress on photosynthetic productivity, gas exchange, and leaf diffusive resistance of Glycine max (L.) Merrill cv Wells II.

Relative growth rate (RGR), leaf water potential (psi w), transpiration rate (Tr), photosynthetic rate (Pn), and stomatal and mesophyll resistances to CO2 exchange were measured or calculated to determine how periodic seismic (shaking) stress decreased dry weight accumulation by soybean (Glycine max [L.] Merrill cv Wells II). Seismic stress was applied with a gyratory shaker at 240 to 280 revolutions per minute for 5 minutes three times daily at 0930, 1430, and 1930 hours. Fifteen days of treatment decreased stem length 21%, leaf area 17%, and plant dry weight 18% relative to undisturbed plants. Seismic stress also decreased RGR 4%, which was due entirely to decreased net assimilation rate. Transpiration decreased 17% and leaf psi w increased 39% 30 minutes after treatment. A reduction in Pn began within seconds after the onset of treatment and had declined 16% after 20 minutes, at which time gradual recovery began. Assimilation rate recovered fully before the next seismic treatment 5 hours later. Resistance analysis and calculation of leaf internal CO2 levels indicated that the transitory decrease in Pn caused by periodic seismic stress was due to increased stomatal resistance on the abaxial leaf surface.

Biomass↗
PubMed1985

Salicylhydroxamic acid potentiates germination of 'Waldmann's Green' lettuce seed.

A combination of salicylhydroxamic acid (SHAM) + cyanide (CN) is known to stimulate dark germination of Lactuca sativa L. seeds. Further studies were done to characterize SHAM and CN action in stimulating dark germination of lettuce seed. Germination was stimulated slightly by either SHAM or CN, whereas when SHAM and CN were combined germination was greatly enhanced. Treatment of seeds with SHAM + CN only during the first 8 hours of hydration stimulated germination as much as did treatment for 72 hours. During the first 8 hours of incubation in SHAM + CN, potentiation (i.e. domancy-breaking) of germination occurs. SHAM alone stimulated potentiation nearly to the level of SHAM + CN but inhibited subsequent radicle elongation, thereby decreasing germination when present for 72 hours. Oxygen must be present for SHAM or SHAM + CN to potentiate dark germination. The ability of SHAM and SHAM + CN to potentiate germination is influenced by O2 concentration and the timing of chemical treatment.

Cell Respiration↗
PubMed1985

Effects of seismic stress on the vegetative growth of Glycine max (L.) Merr. cv. Wells II.

Vegetative plants of soybean [Glycine max (L.) Merr. cv. Wells II] grown in a greenhouse and agitated periodically on a gyratory shaker had shorter stems, less leaf area, and lower leaf and plant dry weight than did undisturbed greenhouse-grown (GG) plants after 16 d of treatment. Outdoor-grown (OG) plants, which were subject to additional environmental stresses including ultraviolet radiation, wind loading, and uncontrolled temperature and humidity fluctuations, were smaller and had less dry weight than GG controls, but growth was not inhibited further by gyratory shaking. Periodic shaking of GG soybeans resulted in the same plant and leaf dry weight as for the OG soybeans. Response of GG plants to mechanical stress depended on light intensity, with minimum growth reduction occurring under full light (FL) level, and maximum growth reduction occurring under lower light levels (24-45% FL). Reduction in dry weight gain due to mechanical stress corresponded to a decrease in relative growth rate (RGR). Decreases in net assimilation rate and leaf area ratio contributed equally to the lower RGR of shaken plants, indicating that seismic stress inhibits dry weight accumulation by decreasing both the photosynthetic efficiency and the assimilatory surface of soybean.

Biomass↗
PubMed1985

Seismic stress effects on reproductive structures of tomato, potato, and marigold.

Periodic seismic (shaking) stress influenced the growth of sexual and asexual reproductive structures of three cultivated species. It delayed anthesis of Lycopersicon esculentum Mill. 'Patio' but not of Tagetes erecta L. 'Jubilee' or Solanum tuberosum L. 'Kennebec'. Shaken 'Jubilee' marigold plants produced the same number of flowers as undisturbed plants, but flowers of shaken plants were smaller. In contrast, seismic-stressed 'Patio' tomato produced fewer buds and flowers, but fruit set was enhanced relative to that of controls. Seismic stress also reduced tuber weight of 'Kennebec' potato, whereas tuber number was unaffected. The overall effect of seismic stress was to reduce the growth of reproductive structures and, in some cases, the number of reproductive structures that developed.

Asteraceae↗
PubMed1985

The Minitron system for growth of small plants under controlled environment conditions.

The design and operation of a system is described in which small plants can be grown under controlled environment conditions. Important features of this "Minitron" system include precise control of temperature and CO2 concentration in a flowing atmosphere. Plants can be grown either hydroponically or in solid root support medium. For either culture method, nutrient solution or water is added from an external reservoir, altering neither atmospheric composition nor temperature equilibrium within a closed Minitron chamber.

Air Conditioning↗
PubMed1985

House dust control and asthma: a placebo-control trial of cleaning air filtration.

Using a placebo-control single-blind crossover trial, we investigated the effects of dust control measures alone and combined with electrostatic and high efficiency particulate air filters in the bedrooms of patients with asthma. Of 12 young asthmatics allergic to house dust and dust mite who entered the trial, nine completed all four 2-week intervals. No statistically significant improvement in symptom scores or peak expiratory flow above that recorded during the placebo interval occurred during any treatment phase. We conclude that house dust suppression adds little to the management of otherwise well controlled young asthmatic patients.

Air Pollution↗