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Biomedical subjects

A Armstrong

Publications and source records attributed to A Armstrong.

At least 19 recordsLinked to original sources
PubMed1991

Physiological and developmental implications of motor unit anatomy.

There is increasing evidence that the architectural design and arrangement of the fibers within a motor unit have important physiological and developmental ramifications. Limited data, however, are available to directly address this issue. In the present study the physiological properties of one motor unit in each of seven cat tibialis anterior (TA) muscles were determined. Each of these units then was repetitively stimulated to deplete the glycogen in all muscle fibers within the unit. Subsequently, the length, type of ending, and spatial distribution of fibers sampled from these physiologically and histochemically typed motor units were determined. Four fast fatigable (FF), one fast, fatigue resistant (FR), and two slow (S) motor units (MU) were studied. The samples consisted of all those glycogen-depleted fibers (9-27) contained within a single fascicle or a circumscribed area of each of the motor unit territories. The mean fiber lengths for the two slow motor units were 35.9 and 45.5 mm. The mean fiber lengths for the fast motor unit samples ranged from 8.8 to 48.5 mm. Some fibers of both the fast and slow units reached lengths of 58 mm. Most of the fibers in the slow units extended the entire distance between the proximal and distal musculotendinous planes, had relatively constant cross-sectional areas, and terminated at the tendon as blunt endings. In contrast, the majority of the fibers in the fast units terminated intrafascicularly at one end, and the cross-sectional area decreased progressively along their lengths, that is, showed a tapering pattern for a significant proportion of their lengths. Therefore, the force generated by units that end midfascicularly would appear to be transmitted to connective tissue elements and/or adjacent fibers. All fibers of a fast unit within a fascicle were located at approximately the same proximo-distal location. Thus, developmentally the selection of muscle fibers by a motoneuron would seem to be influenced by their spatial distribution. The architectural complexities of motor units also have clear implications for the mechanical interactions of active and inactive motor units. For example, the tension capabilities of a motor unit may be influenced not only by the spatial arrangement of its own fibers, but also by the level of activation of neighboring motor units.

Animals↗
PubMed1991

A comparative study of the 'FDA' and 'USDA' methods for the detection of Listeria monocytogenes in foods.

Nineteen laboratories across Canada took part in a comparative study of the 'FDA' and 'USDA' methods for the detection of Listeria monocytogenes in foods and environmental samples. The results show that the enrichment period of the FDA method can be shortened from 7 to 2 days without substantially reducing the number of positive samples. With a limited number of samples, the USDA method proved to be slightly more efficient in isolating L. monocytogenes than the FDA method. Fraser broth, in principle, proved to be useful as a screening tool but is not very selective. Oxford agar and lithium chloride-phenylethanol-moxalactam medium were better than modified McBride's agar in isolating this microorganism.

Agriculture↗
PubMed1991

An evaluation of a logbook for trainees in accident and emergency medicine in the United Kingdom.

The ideal requirements of a logbook for trainees in accident and emergency medicine in the United Kingdom were sought by means of a postal survey of 100 Senior Registrars and recently-appointed Consultants in the specialty. Sixty-two replies were received. An overwhelming majority supported ACLS and ATLS certification, as well as formal training in Management/Clinical Budgeting skills, the use of Information Technology, dealing with medicolegal issues and Disaster Planning. Secondments to General Practice, Regional Poisons Centres and the Emergency Services were similarly recommended. A total of 71% (42 responders) approved of a minimum of 3 years experience in an A&E Department before appointment as a Senior Registrar in the specialty. The majority of responders disapproved of acquiring laboratory-based skills. The results of the survey are discussed and suggestions for the possible role of a logbook are made.

Certification↗
PubMed1991

The phenomenology of Cushing's syndrome: one patient's account.

Cushing's syndrome caused by ectopic secretion of adrenocorticotropic hormone (ACTH) is often a serious disease and a diagnostic dilemma. In the reported patient, the source of ACTH proved to be a benign pulmonary carcinoid tumor. The patient describes his trying experiences through the six months from initial diagnosis to definitive therapy.

Carcinoid Tumor↗
PubMed1990

Increased sensitivity of the rapid hydrophobic grid membrane filter enzyme-labeled antibody procedure for Escherichia coli O157 detection in foods and bovine feces.

Several strains of Escherichia coli O157:H7 artificially inoculated into vegetables and dairy products were recovered on hydrophobic grid membrane filters and enumerated by an enzyme-labeled antibody assay. The mean of the recoveries from 12 fresh vegetables was 108.8%, whereas that from 10 dairy products was 93.2%. Modified tryptic soy broth at 43 degrees C with shaking at 100 rpm provided optimum recovery of the organism from meat, with a sensitivity of less than or equal to 1 CFU/g, which is 10 times more sensitive than direct plating. The method performed equally well with vegetable and dairy products. Tryptic soy broth, however, under the same conditions gave the best results for fecal samples. Of 22 asymptomatic dairy cattle, reported as having positive Brucella titers when assayed with polyclonal antibodies, eight were found to contain E. coli O157 in their feces as demonstrated by the enzyme-labeled antibody assay by using monoclonal antibodies. This finding may explain some of the false-positive Brucella tests.

Animals↗
PubMed1990

The quantity of rhodopsin in human eyes.

The content of rhodopsin in the eyes of 15 donors (30 eyes) was determined. Both retinal and pigment epithelial fractions were collected from each globe, extracted using 1% CTAB, and the rhodopsin difference spectrum of each fraction was obtained separately. The total amount of rhodopsin, obtained by summing the amounts recovered from the retinal and PE fractions, ranged from 2.00 to 11.94 (median: 6.40) nmoles/eye. Previously reported mean values of about 3.5 to 4.0 nmoles per retina have been obtained using a variety of methods. The present higher values, perhaps largely dependent on procedural details described herein, appear plausible given the known concentrations of rhodopsin in rod outer segments, rod outer segment volumes, and number of rods in the human retina.

Adult↗
PubMed1989

Mercaptan and dicarboxylate inhibitors of hamster dihydroorotase.

In mammals, dihydroorotase is part of a trifunctional protein, dihydroorotate synthetase, which catalyzes the first three reactions of de novo pyrimidine biosynthesis. Dihydroorotase catalyzes the formation of a peptide-like bond between the terminal ureido nitrogen and the beta-carboxyl group of N-carbamyl-L-aspartate to yield heterocyclic L-dihydroorotate. A variety of evidence suggests that dihydroorotase may have a catalytic mechanism similar to that of a zinc protease [Christopherson, R. I., & Jones, M. E. (1980) J. Biol. Chem. 255, 3358-3370]. Tight-binding inhibitors of the zinc proteases, carboxypeptidase A, thermolysin, and angiotensin-converting enzyme have been synthesized that combine structural features of the substrates with a thiol or carboxyl group in an appropriate position to coordinate a zinc atom bound at the catalytic site. We have synthesized (4R)-2-oxo-6-thioxohexahydropyrimidine-4-carboxylate (L-6-thiodihydroorotate) and have found that this analogue is a potent competitive inhibitor of dihydroorotase with a dissociation constant (Ki) in the presence of excess Zn2+ ion of 0.17 +/- 0.02 microM at pH 7.4. The potency of inhibition by L-6-thiodihydroorotate in the presence of divalent metal ions decreases in the order Zn2+ greater than Ca2+ greater than Co2+ greater than Mn2+ greater than Ni2+; L-6-thiodihydroorotate alone is less inhibitory and has a Ki of 0.85 +/- 0.14 microM. 6-Thioorotate has a Ki of 82 +/- 8 microM which decreases to 3.8 +/- 1.4 microM in the presence of Zn2+. Zn2+ alone is a moderate inhibitor of dihydroorotase and does not enhance the potency of other inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Amidohydrolases↗
PubMed1989

Kinetic and biochemical heterogeneity in vertebrate chondroepiphyseal regions during development.

The purpose of this study was to see if kinetic and biochemical heterogeneity could be documented in vertebrate chondroepiphyseal regions as they develop from mesenchymal condensations to cartilage. The kinetics of developing proximal and distal femoral chondroepiphyseal regions were studied from early limb bud stage to newborn animals in chicks, mice, and rabbits with thymidine autoradiography. Proteoglycan synthesis in the proximal femoral chondroepiphyseal region of the rabbit was studied with radioactive sulfate incorporation at 28 days of gestation and at 1 and 4 days after birth. The results indicated that these kinetic and biochemical characteristics of the developing chondroepiphyseal regions became heterogeneous very early in development. This early programming of populations of cells for division and for different biochemical functions existed during the fetal period when heterogeneity has been described histologically but has not been well documented.

Animals↗
PubMed1988

Hepatitis B markers in Lancashire police officers.

A total of 284 Lancashire police officers each with a minimum of 5 years experience was tested for evidence of hepatitis B infection. None was hepatitis B surface antigen positive (HBsAg). Three were positive for both antibody to hepatitis B core antigen (anti-HBc) and HBsAg (anti-HBs). Five were positive for anti-HBc alone. Thus the overall prevalence was 2.8% which is within the range reported for blood donors in the UK. There was no association with working in the drug squad or custody office but there was a higher prevalence in those who had worked in the scene-of-crime's squad. However, the numbers were small, and of this group of 28 officers, 2 of the 3 with detectable hepatitis B markers were positive for anti-HBc alone. Therefore for police officers in mixed rural/urban areas of the UK, routine administration of hepatitis B vaccine is not justified although special consideration should be given to those working in selected groups. Further studies are required to ascertain whether there may be an increased risk for police officers working in conurbations.

Adult↗
PubMed1987

Elaboration of neutral proteoglycanase by growth-plate tissue cultures.

This report describes the properties of a neutral protease that was synthesized and secreted into medium by intact cartilaginous growth plate in tissue culture. Bovine cartilaginous growth plate was grown for seven days in tissue culture, during which time the chondrocytes remained viable and metabolically active as determined by quantitation of trypan-blue exclusion and incorporation of 3H-cytidine. Protease activity, assayed by viscometry using proteoglycan monomer from cartilage as a substrate, was absent on day 1 but was present at high levels on days 2 through 5. The protease activity did not require activation and was highest at neutral and alkaline pH. Protease activity was abolished by twenty-millimolar EDTA but was unaffected by pepstatin, iodoacetate, and soybean trypsin inhibitor. In contrast to the high levels of activity of neutral protease that were present in tissue cultures of the intact growth plate, no protease activity could be detected when chondrocytes from the cartilaginous growth plate were grown in cell culture, even after sonication of the cells or activation with aminophenyl mercuric acetate or trypsin. Since hypertrophic chondrocytes probably do not survive the disruption of tissue that is involved in establishing cell cultures, these observations suggest that neutral protease is probably released into the medium by the hypertrophic chondrocytes that are present in the cultures of cartilaginous growth-plate tissue. It appears that the organization of the growth plate in tissue culture, as well as the maturation of proliferating chondrocytes into hypertrophic chondrocytes in tissue culture, may be required for synthesis of the neutral protease and its extracellular secretion by hypertrophic chondrocytes.

Alkaline Phosphatase↗
PubMed1986

cDNA sequence of human beta-preprotachykinin, the common precursor to substance P and neurokinin A.

The nucleotide sequence of cDNA encoding the human substance P precursor, beta-preprotachykinin (beta-PPT), has been determined. The source of mRNA was a human laryngeal carcinoid tumour that contained a high concentration of immunoreactive substance P. The human beta-PPT polypeptide is 129 amino acids long and contains regions encoding substance P and neurokinin A, each flanked by basic amino acid residues. Residues 72-107 of the human beta-PPT polypeptide encode the sequence of neuropeptide K, an N-terminally extended form of neurokinin A recently isolated from porcine brain.

Animals↗
PubMed1986

Effects of gastrin, glutamine, and somatostatin on the in vitro growth of normal and malignant human gastric mucosal cells.

This study evaluated the dose-related trophic effects of glutamine, gastrin, and somatostatin on the in vitro growth of human gastric cancer cells and normal human gastric mucosal cells. Quadruplicate cell cultures were seeded into growth medium with or without glutamine, gastrin, or somatostatin. After 72 hours' incubation, cells were counted and their numbers compared with those of controls. Glutamine and gastrin stimulated the growth of both normal and malignant gastric mucosal cells. Compared with normal cells, the malignant cells responded to these growth factors at lower concentrations. Somatostatin enhanced growth of gastric cancer cells at all concentrations and inhibited growth of normal cells at high concentrations. Further studies on the responsiveness of gastric adenocarcinoma to gastrointestinal tract hormones may elucidate mechanisms of oncogenesis and suggest new therapeutic avenues for patients with gastric cancer.

Adenocarcinoma↗
PubMed1984

Characterization and partial purification of a 5,700 dalton form of substance P-like immunoreactivity from the rat hypothalamus.

Analysis of rat hypothalamic extracts by gel filtration and HPLC revealed the presence of a form of substance P-like immunoreactivity with a molecular weight of approximately 5,700 (6k-SP). 6k-SP is probably an N-terminally extended form of substance P; the peptide may be an intermediate in SP biosynthesis, or may function as a biologically active peptide in its own right.

Animals↗
PubMed1981

Brucellosis.

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Brucellosis↗