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Biomedical subjects

C Clark

Publications and source records attributed to C Clark.

At least 325 records · Page 18Linked to original sources
PubMed1967

Growth response of Nitrosomonas europaea to amino acids.

Growth responses of Nitrosomonas europaea to individual amino acids or vitamins was observed in log-phase cultures, as was the incorporation of carbon-14 labeled amino acids. Nitrite formation and protein synthesis were increased by l-glutamic acid, l-aspartic acid, l-serine, and l-glutamine. l-Lysine, l-histidine, l-threonine, l-valine, l-methionine, and l-arginine were inhibitory. The other amino acids had no effect on growth. All of the uniformly labeled amino acids added at low concentrations were taken up by growing cells and distributed into cell fractions. From 1 to 12% of the added radioactivity was present in cells analyzed in late log phase, depending on the amino acid; glycine and l-serine caused accumulation of the label to the greatest extent, whereas l-aspartic and l-glutamic acids were among those incorporated to the least extent. Aspartic acid increased both cell protein and nitrite values, but did not alter the ratio of protein to nitrite from that found in controls.

Amino Acids↗
PubMed1967

Uptake and utilization of amino acids by resting cells of Nitrosomonas europaea.

Incorporation of selected amino acids by resting cells was studied with regard to effects of concentration, rate and extent of incorporation, cellular distribution, effect of ammonium ion on uptake, and competitive effects. l-Aspartic acid, l-alanine, l-serine, and glycine presented at trace levels were incorporated at rates ranging from 0.11 to 8.2 mumumoles per mg (dry weight) per minute, and maximal incorporation was 11 to 333 mumumoles per mg (dry weight). When glycine and aspartic acid were supplied at substrate level, the rate of incorporation increased 14- and 109-fold, respectively. The presence of ammonium ion further increased both the rate and extent of uptake of glycine and aspartic acid. The distribution of cellular radioactivity arising from (14)C amino acids indicated that cell pool radioactivity was concentrated from 1.2- to 24.5-fold over the external medium. Aspartic acid pool radioactivity accounted for 50% or more of the total cellular radioactivity, whereas radioactivity in glycine and serine pools dropped from initially high levels to 20 to 25% during incubation. The decrease in pool radioactivity with both glycine and serine was accompanied by an increase in other fractions, especially in the cell residue. The growth-inhibiting amino acid l-valine, supplied at substrate level, contributed more carbon per milligram (dry weight) than any other amino acid studied. l-Leucine, in the presence of l-valine, was observed to decrease valine incorporation.

Amino Acids↗
PubMed1966

Effect of mixed culture on Nitrosomonas europaea simulated by uptake and utilization of pyruvate.

Clark, Connie (University of Minnesota, Minneapolis), and E. L. Schmidt. Effect of mixed culture on Nitrosomonas europaea simulated by uptake and utilization of pyruvate. J. Bacteriol. 91:367-373. 1966.-Contamination of a 5-liter culture of Nitrosomonas europaea resulted in enhanced nitrite formation as compared with pure cultures. The dominant contaminant, a yellow-pigmented, heterotrophic bacterium, was isolated and studied both in pure culture and in deliberate mixture with N. europaea. Growth of N. europaea was stimulated in mixed cultures with the heterotrophic isolate to varying degrees, apparently depending on the age and density of autotrophic inocula. Mixed culture stimulation of N. europaea was evidenced only by a shortened lag phase, since post-lag phase growth of the autotroph was equivalent in both pure and mixed cultures. The heterotrophic component had a nutritional requirement for amino acids when grown on simple media; presumably, in the mixed culture system, the heterotroph was provided with amino acids synthesized by the autotroph. The mixed culture effect was reproduced in all essential features by the addition of sodium pyruvate to the nitrification medium. Pure cultures of N. europaea were shown to incorporate sodium pyruvate-2-C(14) during growth. Labeled carbon was widely distributed in cell fractions. The more pronounced and consistent pyruvate effect was observed on old inocula of N. europaea.

Amino Acids↗
PubMedDate not supplied

Reducing the burden of diabetes: managing cardiovascular disease.

Of the threats to health and life that beset the person with diabetes, cardiovascular disease (CVD), particularly coronary heart disease (CHD) but also cerebrovascular and peripheral vascular disease, represent the heaviest burden. The relative risk for CVD is very high for Type 1 diabetes, but the absolute risk, in terms of numbers, is much higher for Type 2. In all societies, diabetes increases cardiovascular risk twofold or more, compared with the local non-diabetic population. Some of the evidence for this diabetes-related increase in cardiovascular risk is reviewed and its relationship to recognised cardiovascular risk factors considered. The explanation of the enhanced susceptibility to atherosclerotic disease in diabetes remains a matter of contention. How much can be explained by greater prevalence in diabetes of such risk factors as hypertension and dyslipidaemia? To what extent is the impact of a given level of risk factor magnified by a co-existing diabetic state? Is the increased cardiovascular morbidity and mortality secondary to risk factors specifically related to the diabetic state itself? Does the explanation lie in altered coagulability due to changes in platelet activation and aggregability, fibrinogen levels, Factor VII, von Willebrand factor or PAI-1, in the concentration or composition of plasma lipoproteins, in defective endothelial cell function or other metabolic abnormalities of the arterial wall? To what extent is cardiovascular risk related to the degree of hyperglycaemia, protein glycation, relative hyperinsulinaemia and insulin resistance? Data from recent epidemiological, intervention and laboratory investigations bearing on causation, management and prevention of CVD in diabetes are reviewed. Evidence for the impact of correction of glycaemia, dyslipidaemia and raised arterial pressure is considered and reasons are adduced for a broad and proactive therapeutic approach with early identification and vigorous correction of key risk factors.

Cardiovascular Diseases↗
PubMedDate not supplied

1H MRS in acute traumatic brain injury.

The objective of this study was to demonstrate 1H MR spectroscopy (MRS) changes in cerebral metabolites after acute head trauma. Twenty-five patients (12 children, 13 adults) were examined with quantitative 1H MRS after closed head injury. Clinical grade (Glasgow Coma Scale [GCS]) and outcome (Rancho Los Amigos Medical Center Outcome Score [ROS]) were correlated with quantitative neurochemical findings. N-acetylaspartate (NAA), a neuronal and axonal marker, was reduced (P < .03-.001). In children, a reduced NAA/creatine plus phosphocreatine (Cr) level and the presence of detectable lipid/lactate predicted bad outcome (sensitivity, 89%; specificity, 89%). The first MRS examination of all patients correlated with ROS versus NAA (r = .65, P < .0001). Although most patients showed MRS abnormalities, striking heterogeneity of 1H MRS characterized the individual patients. 1H MRS identifies multiple patterns of diffuse brain injury after blunt head trauma. There was a strong correlation between MRS and outcome. Future prospective studies will be needed to determine the clinical usefulness of MRS in predicting outcome from closed head injury.

Adult↗
PubMedDate not supplied

The antiviral drug amantadine has a direct inhibitory effect on T-lymphocytes.

We investigated the effect of the antiviral drug amantadine (AmTd) on polyclonal activation of thymic-dependent (T) and thymic-independent (B) lymphocytes from normal mice. In the present studies, T-lymphocytes are defined by their response to concanavalin A (Con A) and B-lymphocytes by their response to lipopolysaccharide (LPS). Polyclonal activator-induced lymphocyte proliferation was assessed by quantifying cellular incorporation of tritiated thymidine. The results show that, in a dose-dependent manner, AmTd exhibits at least 2-fold greater inhibitory activity against Con A-responding T-cells than against LPS-responding B-cells. Further, several findings demonstrate that AmTd has a direct inhibitory effect on T-lymphocytes. First, AmTd pulse treatment of isolated T-cells, but not accessory cells, abolished the T-cell response to Con A. Second, AmTd pulse treatment of the cytotoxic T-lymphocyte line, CTLL-2, markedly reduced their ability to undergo IL-2-induced proliferation. Third, proliferation of T-cells which had already undergone activation by ConA was inhibited by AmTd. Further, the finding that addition of IL-1, IL-2 or both to cultures failed to reverse inhibition of the response to ConA argues that AmTd did not interfere with endogenous production of these lymphokines. Possible implications of these findings are discussed.

Amantadine↗
PubMedDate not supplied

Inhibition of lymphocyte proliferation by amantadine and its isomer, 2-aminoadamantane; impact on Lyt-2+ T cells while sparing L3T4+ T cells.

The present in vitro investigations on amantadine (AmTd) and its isomer 2-aminoadamantane (2-NH2-Adam), and the corresponding analogs, 1-nitroadamantane (1-NO2-Adam) and 2-nitroadamantane (2-NO2-Adam), were undertaken to gain information about molecular features that might have a dominant role in inhibiting T lymphocyte proliferation and to determine whether all, or a subpopulation of thymic-dependent (T) lymphocytes might be impacted by these drugs. Studies were done using lymphocytes from untreated normal mice as well as cloned murine cytotoxic T lymphocytes, CTLL cells. T lymphocytes were defined by their proliferative response to concanavalin A (Con A), and thymic-independent (B) lymphocytes by their proliferative response lipopolysaccharide (LPS). Proliferation of CTLL cells was induced by supplementing the culture medium with lymphokine-containing medium or by adding recombinant interleukin (IL)-2. Proliferation was assessed by quantifying cellular incorporation of tritiated thymidine. The data show that the aminoadamantanes, AmTd and 2-NH2-Adam, impacted on Lyt-2+ T lymphocytes while sparing L3T4+ T lymphocytes. In addition, the data show that the location of the substituent group on the adamantane ring altered the molecule's capacity to modulate lymphocyte activity. And finally, results of studies comparing the inhibitory activity of AmTd and 1-NO2-Adam suggest a non-lysosomal mechanism of action. Possible implications of these findings are discussed.

Adamantane↗
PubMedDate not supplied

Aircraft and road traffic noise and children's cognition and health: a cross-national study.

BACKGROUND: Exposure to environmental stressors can impair children's health and their cognitive development. The effects of air pollution, lead, and chemicals have been studied, but there has been less emphasis on the effects of noise. Our aim, therefore, was to assess the effect of exposure to aircraft and road traffic noise on cognitive performance and health in children. METHODS: We did a cross-national, cross-sectional study in which we assessed 2844 of 3207 children aged 9-10 years who were attending 89 schools of 77 approached in the Netherlands, 27 in Spain, and 30 in the UK located in local authority areas around three major airports. We selected children by extent of exposure to external aircraft and road traffic noise at school as predicted from noise contour maps, modelling, and on-site measurements, and matched schools within countries for socioeconomic status. We measured cognitive and health outcomes with standardised tests and questionnaires administered in the classroom. We also used a questionnaire to obtain information from parents about socioeconomic status, their education, and ethnic origin. FINDINGS: We identified linear exposure-effect associations between exposure to chronic aircraft noise and impairment of reading comprehension (p=0.0097) and recognition memory (p=0.0141), and a non-linear association with annoyance (p<0.0001) maintained after adjustment for mother's education, socioeconomic status, longstanding illness, and extent of classroom insulation against noise. Exposure to road traffic noise was linearly associated with increases in episodic memory (conceptual recall: p=0.0066; information recall: p=0.0489), but also with annoyance (p=0.0047). Neither aircraft noise nor traffic noise affected sustained attention, self-reported health, or overall mental health. INTERPRETATION: Our findings indicate that a chronic environmental stressor-aircraft noise-could impair cognitive development in children, specifically reading comprehension. Schools exposed to high levels of aircraft noise are not healthy educational environments.

Aircraft↗
PubMedDate not supplied

Enzyme-linked immunosorbent (ELISA) determination of aflatoxin B1 in peanut butter: collaborative trial.

Fourteen laboratories in the United Kingdom participated in a collaborative trial of a commercially available ELISA test kit for the determination of aflatoxin B1 in peanut butter. Each laboratory carried out six replicate analyses of each of six individual samples. Collaborators received a control, uncontaminated sample, together with samples prepared by blending naturally-contaminated and control material to give target levels of 8 micrograms/kg, 25 micrograms/kg and 75 micrograms/kg. Two of these samples (8 micrograms/kg and 25 micrograms/kg) were supplied as undisclosed duplicates. The repeatabilities of the assay ranged from 6.2 to 16.7 micrograms/kg. The reproducibilities for aflatoxin B1 concentrations in naturally-contaminated samples ranged from 3.6 to 18.7 micrograms/kg using uncontaminated peanut butter as a reference blank. Modifications to the format of the commercial kit were recommended as a result of the collaborative trial.

Aflatoxin B1↗
PubMedDate not supplied

Toxicity evaluation of petroleum blending streams: inhalation subchronic toxicity/neurotoxicity study of a light catalytic cracked naphtha distillate in rats.

A 15-week, whole-body inhalation study of the vapors of a distillate (LCCN-D) of light catalytic cracked naphtha (CAS no. 64741-55-5, LCCN) was conducted with Sprague-Dawley rats. Target exposure concentrations were 0, 750, 2500, and 7500 ppm for 6 hours/day, 5 days/week. Over the course of the study, animals received at least 65 exposures. For a portion of the control and 7500-ppm groups, a 4-week postexposure period was included in the study. Subchronic toxicity was evaluated using standard parameters. During life, neurotoxicity was evaluated by motor activity assessment and a functional observational battery. Selected tissues from animals in all exposure groups were examined microscopically. Neuropathologic examination of selected neuronal tissues from animals in the control and high-exposure groups was also conducted. No compound-related effects were seen on survival, clinical chemistry, food consumption, or physical signs. No evidence of neurotoxicity was seen at any exposure level. Slight decreases in hematocrit and hemoglobin concentrations were seen in male rats at the end of exposure to 7500 ppm LCCN-D. However, values were within normal physiological ranges and recovery occurred. Slight decreases in mean body weights and body weight gain were observed in high-exposure females during the first 7 weeks of exposure, but this decrease was not seen during the second half of the study. Male rat nephropathy involving hyaline droplet formation and alpha-2micro-globulin accumulation was seen in mid- and high-exposure males, an effect not relevant to humans. The incidence and severity of goblet cell hypertrophy/hyperplasia and respiratory epithelium hyperplasia in nasoturbinal tissues were greater in high-exposure animals, but recovery occurred. None of the effects observed were considered toxicologically significant. The no-observable-adverse-effect level (NOAEL) for subchronic and neurotoxicity of LCCN-D was > or = 7500 ppm.

Alkanes↗
PubMedDate not supplied

The gastric bubble: medicine, magic or mania?

This paper is presented to acquaint the GIA with a new medical procedure that is rapidly gaining popularity throughout the United States. It includes a brief discussion of the medical device itself and the technique of implantation as well as indications and contraindications for its use. In addition, an overview of the program developed at Placentia-Linda Community Hospital, Placentia, CA, is offered. Personal reflections are also rendered regarding the unique nursing opportunities afforded by this procedure and its accompanying follow-up program. In conclusion, this paper will substantiate, with personal experience and early supportive research data, the parallels between the medicinal value, the magic, and the mania accompanying the Gastric Bubble.

Endoscopy, Digestive System↗