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Biomedical subjects

A Sellers

Publications and source records attributed to A Sellers.

At least 19 recordsLinked to original sources
PubMed2000

Assessment of visual-motor coordination in 6- to 11-yr.-olds.

The concurrent and content validity of the Rey-Osterrieth Complex Figure Test and the Beery Developmental Test of Visual-Motor Integration-Third Revision were investigated through correlational analysis. 432 children, ages 6 to 11 years, were administered both tests. Across age groups participants performed better on both measures, providing support for the similarity of the measures and their sensitivity to the development of visuomotor integration. Although analysis indicated considerable overlap in the content of the two scales, the shared variance ranged from 7% to 31%, depending on the age of the child. The Rey-Osterrieth figure is composed of overlapping squares, rectangles, triangles, and various other shapes. Given this complex combination, scores on this test reflect the examinees' visual organization and motor planning skills. On the other hand, the Beery test consists of a series of shapes which progress from simple figures to more complex ones. Because the figures become more difficult to copy, the score on this test reflects the examinees' developmental level of visuomotor ability. Despite these differences in test stimuli and interpretation of performance, the present study showed considerable shared variance in the scores of the examinees who took both tests. Finally, local norms for the Rey-Osterrieth figure using the scoring approach of E. M. Taylor (1959, adapted from Osterrieth, 1944) and including standard scores are presented for children ages 6 to 11 years.

Age Factors↗
PubMed1998

Advancing from flexible sigmoidoscopy to colonoscopy in rural family practice.

This paper describes the background, experience, training, and preceptorship of a rural family physician that culminated in provision of diagnostic and therapeutic colonoscopy to his patients. Initial training took place in a two-day continuing medical education course. Subsequent training consisted of one-on-one training in 11 colonoscopies and five polypectomies, correspondence, recommended readings, a one-on-one preceptorship, and telephone consultation. Training was provided by University of Tennessee faculty who were experts in the area of colonoscopy and polypectomy procedures. The outcomes of 250 consecutive colonoscopies performed by the rural family physician are documented here. Training requirements vary widely by professional organization and subspecialty. Some subspecialists have recommended as many as 100 supervised colonoscopies and 25 polypectomies as a minimum training requirement for hospital privileges. It is our contention that unnecessarily high training requirements add to educational costs and may restrict qualified rural physicians from providing these services.

Adolescent↗
PubMed1985

Ascorbic acid stimulates the resorption of canine articular cartilage induced by a factor derived from activated rabbit macrophages.

Articular cartilage explants from the knees of mongrel dogs release 5-10% of their proteoglycan content spontaneously when cultured for 4 days in serum-free modified Bigger's medium. A factor synthesized and secreted by lipopolysaccharide-stimulated rabbit macrophages can stimulate this release of proteoglycan by 2 to 3-fold. The release of proteoglycan in response to macrophage factor is maximal in the presence of 1.5-50 micrograms/ml L-ascorbic acid. In the absence of ascorbate, or with high levels of ascorbate (150 micrograms/ml), the effect of the factor is diminished by 50%. D-isoascorbate, reduced glutathione, or dithiothreitol cannot substitute for L-ascorbate in producing this effect, while dehydroascorbate can.

Animals↗
PubMed1980

The extraction of a neutral metalloproteinase from the involuting rat uterus, and its action on cartilage proteoglycan.

1. Homogenates of rat uteri removed 1 and 2 days post partum were centrifuged at 6000 g. Both pellets and supernatants degraded Azocoll, a general proteinase substrate, at pH 7.5. More than 80% of the total activity was in the pellet fraction. 2. Part of the pellet activity was in a latent form. Trypsin and 4-aminophenylmercuric acetate (a thiol-blocking agent) both activated this latent form, indicating that it is an enzyme--inhibitor complex. An endogenous serine proteinase activated part of the latent enzyme during the assay. 3. The enzyme activity was low before parturition and after involution; it was highest during the first 2 days post partum, when the largest losses of uterine wet weight and matrix macromolecules occur. 4. Up to 70% of the enzyme in the pellets was extracted by heating at 60 degrees C for 4 min in 0.1 M-CaCl2/0.05 M-Tris/HCl, pH 7.5. Approx. 30% of the extracted enzyme was still latent. 5. The extracted enzyme was a metalloproteinase, since it was inhibited completely by 1,10-phenanthroline, but not by inhibitors of thiol or serine proteinases. 6. The enzyme was further purified 15--30-fold by gel chromatography and precipitation with (NH4)2SO4. The apparent molecular weight, estimated by gel filtration, was 24000 for the latent form and 12000 for the active form. The pH optimum was 7--7.5. 7. The enzyme also degraded cartilage proteoglycan. This activity was studied by viscometry and the products were analysed by analytical ultracentrifugation. The major product had a mol.wt. of approx. 100000. The sites of cleavage were in the protein core, since no free oligosaccharides were detected. 8. This neutral metalloproteinase is distinct from uterine collagenase and from a uterine metal-dependent endopeptidase that hydrolyses a heptapeptide related to collagen.

Animals↗
PubMed1980

Effect of tensile mechanical stress on the synthesis of metalloproteinases by rabbit coronal sutures in vitro.

The application of a continuous tensile mechanical stress (30 g) to explants of coronal sutures from newborn rabbits (1-2 days) produced increases in enzyme activity of 33.7% for collagenase, 95.2% for gelatinase, and 35.9% for NMP III over a 4-day culture period. All three activities were in latent form and required activation with either 4-APMA or trypsin. The increases in enzyme activities were not accompanied by an alteration in the degradation of structural proteins. This was due to the ability of the cells to synthesize an inhibitor (mol wt 29,000 daltons) which complexed the increased quantities of enzyme. This necessitated a substantial stimulation of inhibitor production because there was still a residue of free inhibitory activity in the media of stressed cultures after 4 days. We previously showed using the same model system that coronal sutures respond to tensile mechanical stress by a two-fold increase in collagen synthesis. The present data suggest that when the priority of the cell population is the synthesis of structural proteins, the inhibitor, in addition to preventing the hydrolysis of newly synthesized peptides, also maintains matrix degradation at normal turnover levels.

Animals↗
PubMed1979

Rabbit cranial sutures in vitro: a new experimental model for studying the response of fibrous joints to mechanical stress.

An organ culture system has been developed whereby mechanical stress can be applied to cranial sutures under controlled experimental conditions. The application of a continuous tensile mechanical stress (30 g) to cranial sutures from newborn rabbits (1--2 days) was accompanied by a significant increase in the incorporation of 3H-leucine and 3H-proline into suture protein. The specific activities of 3H-hydroxyproline indicated that mechanical stress produced a two-fold increase in the incorporation of 3H-proline into collagen. However, the proportion of the total radioactivity recoverable in collagen (45.63 +/- 2.33% for nonstressed; 40.58 +/- 2.17% for stressed sutures) was not significantly different. These data suggest that the increase in collagen synthesis occurs as part of a general stimulation of protein synthesis, and do not support the view that mechanical stress is the principal mechanism regulating the turnover of collagen in fibrous joints. These initial studies demonstrate that an in vitro experimental model has considerable potential for investigating the morphological and metabolic response of fibrous joints to mechanical deformation.

Animals↗
PubMed1978

Neutral metallo-proteinases of rabbit bone. Separation in latent forms of distinct enzymes that when activated degrade collagen, gelatin and proteoglycans.

Rabbit bones in culture produce specific collagenase and neutral metallo-proteinase activity in latent forms that can be activated by either 4-aminophenylmercuric acetate or trypsin. Latent neutral metallo-proteinase activity was resolved by gel filtration into two enzymes, distinct from collagenase, that degrade gelatin and cartilage proteoglycans.

Animals↗
PubMed1977

Identification and partial characterization of an inhibitor of collagenase from rabbit bone.

Bone explants from foetal and newborn rabbits synthesize and release a collagenase inhibitor into culture media. Inhibitor production in the early days of culture is followed first by latent collagenase and subsequently active collagenase in the culture media. A reciprocal relationship exists between the amounts of free inhibitor and latent collagenase in culture media, suggesting strongly that the inhibitor is a component of the latent form of the enzyme. Over 90% of the inhibitory activity of culture media is associated with a fraction of apparent mol.wt. 30000 when determined by gel filtration on Ultrogel AcA 44. The inhibitor blocks the action of rabbit collagenase on both reconstituted collagen fibrils and collagen in solution. It inhibits the action of either active collagenase or latent collagenase activated by 4-aminophenylmercuric acetate. Latent collagenase activated by trypsin is usually much less susceptible to inhibition. The activity of the inhibitor is destroyed by heat, by incubation with either trypsin or chymotrypsin and by 4-aminophenylmercuric acetate. Collagenase activity can be recovered from complexes of enzyme (activated with 4-aminophenylmercuric acetate) with free inhibitor by incubation with either trypsin or 4-aminophenylmercuric acetate, at concentrations similar to those that activate latent collagenase from culture media. The rabbit bone inhibitor does not affect the activity of bacterial collagenase, but blocks the action of collagenases not only from a variety of rabbit tissues but also from other mammalian species.

Animals↗
PubMed1977

A new factor that may control collagen resorption.

Specific collagenases responsible for the initial enzymic step leading to degradation of the collagen fibrils of connective tissues have been found in both latent and active forms. The most important factor controlling the local activity of collagenase extracellularly may be an inhibitor that is synthesised by connective tissues, and it is proposed that latent enzymes are all enzyme-inhibitor complexes.

Animals↗
PubMed1977

The detection and characterisation of collagenase inhibitors from rabbit tissues in culture.

As tissue cultures, rabbit bone, skin and non-gravid uterus synthesise inhibitors of collagenase (EC 3.4.24.3). An assay for the inhibitors is described and their action on collagenase from different tissue sources demonstrated. Evidence for the involvement of the tissue inhibitors of collagenase in the latency of the enzyme in culture media is presented. Latent collagenase was activated by treatment with 4-aminophenylmercuric acetate, and then reacted with the inhibitors to form inactive complexes with properties similar to the naturally occurring latent enzyme forms. The associated changes in molecular weight are detailed, and discussed in relation to the observations of other workers concerning the extracellular control of collagenase activity.

Animals↗
PubMed1977

Evidence that latent collagenases are enzyme-inhibitor complexes.

Specific collagenase from the culture media of various rabbit tissues and cells exists in active and latent forms. Latent collagenase is most effectively activated with 4-aminophenylmercuric acetate, a thiol-blocking reagent, strongly suggesting that latent forms are enzyme-inhibitor complexes. A collagenase inhibitor from bone cultures, which may be closely related to the inhibitor of such latent enzyme complexes, was partially characterized.

Animals↗