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Biomedical subjects

A V Barker

Publications and source records attributed to A V Barker.

4 recordsLinked to original sources
PubMed1999

Symptoms of Raynaud's phenomenon in an inner-city African-American community: prevalence and self-reported cardiovascular comorbidity.

The objective of this study was to determine the prevalence of symptoms and the morbidity associated with Raynaud's phenomenon (RP) among African Americans. A total of 2196 randomly selected residents of an inner-city community, in Baltimore, completed a health-assessment survey. Symptoms of RP consisted of cold sensitivity plus cold-induced white or blue digital color change. One third (n = 703) reported cold sensitivity and 14% (n = 308) reported digital color change; 84 residents with symptoms of RP were identified, yielding an overall prevalence rate of 3.8% (95% confidence interval [CI] 3.0-4.6). RP was associated with poor or fair health status (odds ratio [OR] = 1.82, CI 1.18-2.81), heart disease (OR = 2.32, CI 1.39-3.87), and stroke (OR = 2.20, CI 1.17-4.15), after adjustment for age, gender, and physician-diagnosed arthritis. The prevalence of symptoms of RP in this African-American community is comparable to published reports from other populations. These community-based data suggest that identification of RP among African Americans should raise consideration of possible comorbidity, particularly cardiovascular disease.

Adult↗
PubMed1967

Structure and function of tomato leaf chloroplasts during ammonium toxicity.

Ammonium toxicity resulted in morphological modifications of tomato leaf chloroplasts. The chloroplasts, which are normally flattened around the protoplast periphery, became ellipsoidally rounded and dispersed through the protoplasm. The first apparent effect of plastid degradation was development of many vesicles from the fretwork. Later the grana lamellae swelled, and some disappeared. Eventually, distinct grana could not be detected.Ammonium accumulation, chlorophyll loss, and photosynthetic decrease occurred simultaneously. Initial changes in these processes preceded the detection of modifications of fine structure; however, each continued with further breakdown of the chloroplasts.

Journal Article↗
PubMed1966

Root environment acidity as a regulatory factor in ammonium assimilation by the bean plant.

Previous experiments have revealed a much greater efficiency of ammonium utilization by bean plants (Phaseolus vulgaris L.) when the acidity of the ambient medium was maintained at near-neutral conditions with carbonates or hydroxides. The present investigation, in which (15)N-labeled ammonium was used, permitted an assessment of the origin of nitrogen in tissue nitrogen pools with and without acidity control (CaCO(3) treated and untreated, respectively) in the root environment. Control of acidity resulted in greater ammonium uptake and greater incorporation into the amino fraction, amide, and ethanol-insoluble nitrogen by the root tissue. These differences were clearly evident by the fifth day after ammonium nitrogen had been applied.Shoots of the untreated plants rapidly accumulated free ammonium and amino nitrogen. A substantial portion of both fractions came from pre-existing nitrogen in the plants, indicating significant protein degradation. No evidence was found for such degradation in the roots of the untreated plants or in either roots or shoots of CaCO(3) treated plants. The data indicate that control of ambient acidity in the root environment during ammonium absorption enhanced the conversion of entering ammonium to organic nitrogen compounds in the root tissue thereby restricting movement of free ammonium to shoots. Consequently, the detrimental effects of high ammonium concentrations in the leaves were largely prevented.

Journal Article↗