Search PubMed⌕ Search

Biomedical subjects

A Stevens

Publications and source records attributed to A Stevens.

At least 235 records · Page 13Linked to original sources
PubMed1987

A 5'----3' exoribonuclease of human placental nuclei: purification and substrate specificity.

An exoribonuclease that hydrolyzes single-stranded RNA by a 5'----3' mode yielding 5'-mononucleotides has been purified from human placental nuclei. Chromatographic studies of crude placental nuclear extracts suggest that the enzyme is a relatively abundant nuclear RNase. Poly(A) is degraded by a processive mechanism while rRNA is degraded in a partially non-processive manner, possibly because of its secondary structure. The enzyme has an apparent molecular weight of 113,000, derived from determinations of the Stokes radius (43 A) and sedimentation coefficient (6.3 S). Substrates with 5'-phosphomonoester end groups are 10-20 times better than 5'-dephosphorylated substrates. The locale of the enzyme in nuclei of normal human cells as well as its mode of action suggest a role in nuclear RNA processing or turnover.

Cell Nucleus↗
PubMed1987

Duodenal trauma.

Fifteen cases of duodenal trauma that presented to Westmead Hospital between 1979 and July 1986 are reviewed. There were 12 blunt injuries, nine caused by motor vehicle accidents. Three patients sustained penetrating injuries, two due to stab wounds. Repair for blunt laceration or incised wound was by primary closure or serosal patch repair, most often with decompressive t-tube duodenostomy. No leak from the duodenal repair occurred in any patient. Two patients died. This was not due to complications of the duodenal injury. Pyloric exclusion, duodenal diverticulization or pancreaticoduodenectomy was not considered necessary in any patient. Morbidity of duodenal haematoma in the form of continuing abdominal pain may be avoided by intra-operative drainage.

Accidents, Traffic↗
PubMed1987

Isolated tuberculous hepatic abscess.

Tuberculous hepatic abscess occurs rarely, most of these being associated with tuberculosis at other sites. Only 11 reports of isolated tuberculous hepatic abscess have been made in the English literature. A further case of isolated tuberculous hepatic abscess is reported with particular emphasis on the difficulty that may be encountered in reaching the correct diagnosis.

Adult↗
PubMed1987

Osteomalacia and femoral neck fractures in the elderly patient.

In a series of over 1000 elderly patients with femoral neck fracture, who were routinely screened by iliac crest bone biopsy, a 2% prevalence of osteomalacia was found. This low figure suggests that osteomalacia is not a significant predisposing factor in the development of these fractures and that routine screening is not cost-effective.

Aged↗
PubMed1987

Screening for osteomalacia in elderly patients with femoral neck fractures.

In this study 201 elderly patients with femoral neck fractures were compared with 30 osteomalacic patients with the same injury. Hypocalcaemia and a raised alkaline phosphatase level are common biochemical abnormalities in elderly patients with femoral neck fractures. In only a minority of patients, however, were they associated with histologically proven osteomalacia. By using the combination of hypocalcaemia and a raised alkaline phosphatase it is possible to identify a subgroup (approximately 10% of all admissions) in whom osteomalacia is relatively likely.

Aged↗
PubMed1987

Isolation of alpha-crystallin subunits by gel filtration.

In the presence of 0.1 M glycine, pH 2.5, alpha-crystallin dissociates into aggregates containing only alpha A chains plus monomeric alpha B chains. Advantage has been taken of this to develop a method for the purification of the alpha A and alpha B chains by gel filtration on Sephadex G-75. This method gives high yields of purified subunits and avoids the risk of carbamylation associated with other methods which use high concentrations of urea.

Animals↗
PubMed1987

Cervical vertigo diagnosed by posturography? Preliminary report.

Posturographic recording with the patient's head in retroflexion has been proposed as a reliable test for diagnosing cervical vertigo. The clinical experience suggests that a positive result in this test-condition could be accepted as suggestive for cervical involvement, when other data corroborate it, but that it is not per se pathognomonic. In fact, this test is negative in most cases with other cervical indications, whereas it has been found positive, in cases with no cervical indications. A positive test, however, is significantly more frequent in "cervical" cases. On the other hand, otolithic influence upon the test-performance has also to be taken into account.

Adult↗
PubMed1987

Aminoglycoside antibiotic treatment of human fibroblasts: intracellular accumulation, molecular changes and the loss of ribosomal accuracy.

The aminoglycoside antibiotic, G418, was rapidly endocytosed by human fibroblasts. The endocytic uptake comprised two phases. A rapid phase in which G418 was first adsorbed to the cell surface, followed by a slower rate of uptake of 7 to 11 micrograms/mg cell protein/24 h. The rapid uptake was independent of temperature and a fluorescent derivative of G418 could be seen bound to the cell surface. This evidence suggests a nonspecific adsorption mechanism. The slower rate of accumulation may arise from fluid-phase pinocytosis. The effects of G418 and paromomycin on protein synthesis in vivo and in vitro were compared and it was concluded that G418 was more active on mammalian ribosomes. Finally, changes in the pattern of cellular proteins during treatment with either aminoglycoside were found only with G418. The changes in the pattern of proteins suggest the synthesis of stress proteins in treated cells. This change in pattern may be interpreted as a cellular response to abnormal protein synthesis arising from a loss of fidelity or some inhibitory function of G418 on membrane metabolism which may lead to a shortening of cellular life span.

Anti-Bacterial Agents↗
PubMed1986

Novel specificity of an endoribonuclease of yeast.

Investigations of the cleavage specificity of a cyclizing endoribonuclease of yeast show that it hydrolyzes Y-A bonds of single-stranded regions of RNA and that oligonucleotides are hydrolyzed poorly. The stringent specificity of the enzyme suggests that it may be useful for generating specific fragments of polyribonucleotides. An isolation technique employing ethanol extraction has now been used to isolate the enzyme free of other RNases, and the studies show that it is a small protein, 10 kDa or less in molecular mass.

Endoribonucleases↗
PubMed1986

Inhibition of chloride secretion by BaCl2 in the rectal gland of the spiny dogfish, Squalus acanthias.

In the rectal gland of the spiny dogfish (Squalus acanthias), chloride enters the cell via a cotransport system together with sodium and potassium in a 2 Cl-: 1 Na+: 1 K+ stoichiometry. The system is energized by the electrochemical potential for sodium directed into the cell. Sodium is extruded from the cell by Na-K-ATPase located on the basolateral cell membrane. Chloride leaks into the lumen following a favorable electrical gradient. Potassium is thought to recirculate across the basolateral cell membrane. Since barium ions inhibit the efflux of potassium from cells we used barium chloride to explore the role of potassium in the process of stimulated secretion of chloride by the gland. The secretion of chloride was stimulated with theophylline 2.5 X 10(-4)M and dibutyryl cyclic AMP 5 X 10(-5)M. Ba++ inhibited the secretion of chloride in a way that was reversible and dose dependent. The reduction in secretion was associated with a parallel fall in transglandular electrical potential. Inhibition was half maximal at a concentration of Ba++ of 10(-3)M. The reduction in efflux of potassium produced by Ba++ presumably decreases the potassium diffusion potential, thus reducing the electronegativity of the cell and dissipating the driving force for chloride across the apical cell membrane. Recirculation of K+ across the basolateral border of the cell would thus be essential for the maintenance of chloride secretion by the gland.

Animals↗
PubMed1986

Severe cutaneous reactions to captopril and enalapril; histological study and comparison with early mycosis fungoides.

A severe non-dose related skin eruption attributable to treatment with captopril was recently reported: this is distinct from the dose related rashes that have been widely described. Ultrastructural and immunohistochemical studies were carried out to determine in detail the histological features of this eruption: the histological appearances were similar to those found in early mycosis fungoides, so that this disease was erroneously diagnosed in one case. Unlike most other complications resulting from treatment with Captopril, an indistinguishable rash can result from treatment with enalapril, a newer angiotensin converting enzyme inhibitor.

Captopril↗
PubMed1986

Isolated rectal gland cells: oxygen consumption and hormonal stimulation.

Cells isolated from rectal glands of Squalus acanthias, using collagenase and hyaluronidase digestion, retained normal morphological characteristics as judged by light microscopy of 1-micron plastic sections. Their oxygen consumption per unit weight was comparable to that of intact rectal gland studied either in situ, or by isolated perfusion, as well as that of rectal gland slices. Cellular respiration was stimulated by dibutyryl cyclic AMP and theophylline or by vasoactive intestinal peptide which stimulate secretion of chloride by the intact gland. Stimulated oxygen consumption was inhibited by ouabain and bumetanide and was proportional to the concentration of sodium or chloride in the incubation solution. The oxygen consumption of these cells parallels the secretory and metabolic behavior of the intact rectal gland, suggesting that it reflects energy demands for ion transport. The relative ease with which a homogeneous preparation of viable and active cells can be obtained and the apparent preservation of many of their key functional characteristics make this preparation a useful tool for the study of hormone-stimulated ion transport.

Adenosine↗
PubMed1985

Biosynthesis and Degradation of a Wheat Embryo Cytokinin-Binding Protein during Embryogenesis and Germination.

The accumulation and degradation of a wheat (Triticum durum) embryo cytokinin-binding protein (CBF-1) was followed during embryo development and germination by its N(6)-benzyladenine (BA) binding activity and immunological reactivity (rocket immunoelectrophoresis and Western blotting). Both BA binding activity and CBF-1 appeared at 2 weeks post-anthesis and rose sharply between 2 to 4 weeks before leveling off to approximately 47 micrograms per embryo (9% of the soluble embryo protein at maturity). In vitro translation of polyadenylated RNA from 20-day-old embryos yielded a polypeptide which was immunoprecipitable with anti-CBF-1 IgG and migrated closely to the 54-kilodalton CBF-1 polypeptide on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon germination, both the amount of CBF-1 and BA binding activity dropped to low levels within 3 days. The data are discussed in relation to the possible role of CBF-1 as a regulator of cytokinin availability, and comparisons are drawn between the structural and biosynthetic similarities found between CBF-1 and the vicilin storage proteins of legumes. An improved method for isolating undegraded CBF-1 from whole seeds is also presented.

Journal Article↗
PubMed1985

Frozen sections of bone biopsies in metabolic and other bone diseases.

Frozen sections of bone trephine and needle biopsies can be satisfactorily cut in a standard cryostat and, when stained with haematoxylin and eosin, they enable a rapid diagnosis to be made in a wide range of metabolic bone disorders including Paget's disease, osteoporosis, osteomalacia, hyperparathyroidism and renal osteodystrophy. Neoplastic disease of bone may also be diagnosed using the same technique. A tissue diagnosis can be established within an hour of the biopsy being taken, instead of the 1-3 weeks required for resin section diagnosis, with a consequent potential saving in further costly biochemical and radiological investigations, a possible shortening of the patient's stay in hospital and earlier initiation of correct treatment. The method is quick, reliable and highly cost-effective; it is of particular value in laboratories with insufficient workload to justify the expenditure on specialized microtomes and reagents for resin embedding.

Biopsy↗
PubMed1985

Pyrimidine-specific cleavage by an endoribonuclease of Saccharomyces cerevisiae.

An endoribonuclease with pyrimidine cleavage site specificity was isolated from Saccharomyces cerevisiae. The enzyme had a pH optimum of 6 to 7 and did not require a divalent cation. It was inhibited by 5 X 10(-5) M ethidium bromide, although it appeared to be single strand specific. The enzyme gave a limited cleavage of yeast mRNA and rRNA, yielding products that were terminated with pyrimidine nucleoside 2',3'-cyclic phosphate. The bonds between pyrimidine and A residues constituted more than 90% of the scission sites when the average product size was 50 nucleotides. Homopolyribonucleotides were cleaved poorly. Poly(A,U) was cleaved rapidly, and analysis of the products of poly(A,U) hydrolysis showed a very stringent cleavage of U-A bonds.

Endoribonucleases↗