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Biomedical subjects

R Walker

Publications and source records attributed to R Walker.

At least 145 records · Page 8Linked to original sources
PubMed1998

Acute bone pain following renal transplantation: differentiation between benign bone edema and avascular necrosis.

Two patients are reported who presented within the first 3 months posttransplantation with acute bone pain where serial magnetic resonance imaging (MRI) allowed differentiation between bone edema, which resolved spontaneously, and avascular necrosis (AVN) requiring core decompression. Case 1 had ill-defined images consistent with bone edema that resolved, whereas case 2 developed well-demarcated lesions in the femoral condyles and tibial epiphyses which were confirmed as AVN at surgery. Alternative explanations for bone edema were not evident. We would suggest that in any transplant recipient who develops acute bone pain, MRI is the initial diagnostic modality of choice. Evidence of development of well-demarcated lesions on serial MR scans indicate early AVN. However, on current evidence it is difficult to predict which lesions will progress and until greater experience becomes available, we would recommend intraosseous plethysmography and venography so that incipient or early AVN can be treated by core decompression of the affected bone.

Acute Disease↗
PubMed1998

Henoch-Schonlein purpura: the Chandigarh experience.

OBJECTIVE: To determine the clinical profile of children with Henoch-Schonlein purpura (HSP). DESIGN: Hospital based descriptive follow-up study. SUBJECTS: 45 patients attending the Pediatric Rheumatology and Immunology clinic over the last 4 years. RESULTS: The patients were aged between 2.5-12 years with a male to female ratio of 2:1. All cases had palpable purpura. Gastrointestinal involvement was seen in 38 patients, with abdominal pain in 35 (78%) and lower GI bleed in 21 (47%). Large joint arthritis occurred in 60%. Renal involvement was seen in 14 subjects (31%). Major renal involvement occurred in 9 patients, with nephritic syndrome in 6 and nephrotic syndrome in 3 cases. Five patients had minor urinary abnormalities; 6 patients with major renal involvement and crescentic glomerulonephritis were treated with high dose pulse steroid therapy followed by oral prednisolone and azathioprine for 12-18 months. Normalization of urinary abnormalities occurred in these patients over 4-8 months and presently all are normotensive and off antihypertensive drugs. CONCLUSIONS: HSP in children is a common form of vasculitis. Though short term results in HSP nephritis have been good, long term prognosis in those with major renal involvement would remain guarded.

Adolescent↗
PubMed1997

Bioactivation of mushroom hydrazines to mutagenic products by mammalian and fungal enzymes.

Agaritine (N2-[L-(+)-glutamyl]-4-(hydroxymethylphenyl)hydrazine), the principal hydrazine found in the edible mushroom Agaricus bisporus, as well as the N'-acetyl derivative of 4-(hydroxymethyl)phenylhydrazine and 4-(hydroxymethyl)benzene diazonium ion, as the tetraborate salt, considered as the putative proximate and ultimate carcinogens of agaritine, were all synthesised chemically. The mutagenicity of these compounds and of 4-hydrazinobenzoic acid, a precursor of agaritine biosynthesis in mushroom, was investigated in the Ames test, using Salmonella typhimurium strain TA104, in the absence and in the presence of either mushroom tyrosinase or rat hepatic cytosol as activation systems. In the absence of an activation system the diazonium ion was clearly the most mutagenic of the four compounds studied. When tyrosinase was used as activation system, the mutagenicity of N'-acetyl-4-(hydroxymethyl)phenylhydrazine was enhanced; glutathione and superoxide dismutase markedly suppressed the mutagenic response. When the mutagenicity of the four compounds was evaluated in the presence of rat hepatic cytosol, an increase was seen only in the case of N'-acetyl-4-(hydroxymethyl)phenylhydrazine; this was shown to be due to deacetylation releasing the more mutagenic free hydrazine. Collectively, the above data are compatible with an activation of agaritine that involves an initial loss of the gamma-glutamyl group followed by microsomal oxidation of the free hydrazine to generate the diazonium ion. Also of interest is the observation that mushroom tyrosinase can convert N'-acetyl-4-(hydroxymethyl)phenylhydrazine to mutagenic product(s); whether these products contribute to the mutagenicity of mushroom extracts remains to be established.

Agaricus↗
PubMed1997

Women with past history of bone fracture have low spinal bone density before menopause.

AIMS: Recent work from our laboratory has demonstrated that young girls with bone fractures have low spinal bone density more often than girls who have never fractured. This study was undertaken to determine whether adult women approaching menopause who have any past history of fracture have lower spinal density than women who have never fractured. METHODS: A lifetime fracture history was taken from all premenopausal women (n = 59) enrolled in a clinical trial examining the effect of menopause on cardiac risk. Bone mineral density of the lumbar spine was measured at study entry by dual energy x-ray absorptiometry (Lunar DPX-L) and results from patients with and without fracture were compared. RESULTS: Women with a previous history of fracture (n = 23) had significantly lower bone density (6% less) than the women who had never broken a bone (n = 36). CONCLUSIONS: We conclude that women who report a previous history of fracture, either as young adults or in childhood, should be targeted for perimenopausal screening for osteoporosis since they are likely to have lower bone density and a greater risk of future fracture than women with no past history of fracture.

Absorptiometry, Photon↗
PubMed1997

Formation of DNA repair intermediates and incision by the ATP-dependent UvrB-UvrC endonuclease.

The Escherichia coli UvrB and UvrC proteins play key roles in DNA damage processing and incisions during nucleotide excision repair. To study the DNA structural requirements and protein-DNA intermediates formed during these processes, benzo[a]pyrene diol epoxide-damaged and structure-specific 50-base pair substrates were constructed. DNA fragments containing a preexisting 3' incision were rapidly and efficiently incised 5' to the adduct. Gel mobility shift assays indicated that this substrate supported UvrA dissociation from the UvrB-DNA complex, which led to efficient incision. Experiments with a DNA fragment containing an internal noncomplementary 11-base region surrounding the benzo[a]pyrene diol epoxide adduct indicated that UvrABC nuclease does not require fully duplexed DNA for binding and incision. In the absence of UvrA, UvrB (UvrC) bound to an 11-base noncomplementary region containing a 3' nick (Y substrate), forming a stable protein-DNA complex (Kd approximately 5-10 nM). Formation of this complex was absolutely dependent upon UvrC. Addition to this complex of ATP, but not adenosine 5'-(beta,gamma-iminotriphosphate) or adenosine 5'-(beta, gamma-methylene)triphosphate, caused incision three or four nucleotides 5' to the double strand-single strand junction. The ATPase activity of native UvrB is activated upon interaction with UvrC and enhanced further by the addition of Y substrate. Incision of this Y structure occurs even without DNA damage. Thus the UvrBC complex is a structure-specific, ATP-dependent endonuclease.

Bacterial Proteins↗
PubMed1997

Carbonic anhydrase II and carbonic anhydrase-related protein in the cerebellar cortex of normal and lurcher mice.

The developmental profiles of carbonic anhydrase II (CA-II) and a carbonic anhydrase related protein (CARP) were studied in rat and mouse cerebella. Enzyme histochemistry, immunohistochemistry, in situ hybridisation and Western blotting were used to study the synthesis and expression of these enzymes in cerebellar sections from age matched control, CA-II deficient and lurcher mice, the latter being characterised by Purkinje cell degeneration. Both CA-II and CARP were first found to be expressed in the Purkinje cells in the 9 day old mouse, and the immunoreactivity of both peptides increased with time. Immunohistochemistry showed more intense staining of CARP than of CA-II in Purkinje cells throughout the developmental profile of the mouse, and this was mirrored by the mRNA levels determined by in situ hybridisation. Immunohistochemistry of CA-II and CARP also demonstrated the progressive dendritic growth of the mouse and rat Purkinje cells. CA-II and CARP immunoreactivity ceased by the end of cerebellar maturation. The onset of Purkinje cell degeneration was detected at day 10 in the lurcher mouse, with concomitant marked decrease in CA-II level: however CARP expression was found to be unchanged. By postnatal day 16 neither CA-II mRNA, protein, nor activity was detectable in contrast to CARP which remained at a decreased level unit the Purkinje cells population had completely degenerated. Our findings suggest a role of CA-II in the degenerative processes of the lurcher Purkinje cells, with CARP playing an important role in the development and maturation of the cerebellar cortex.

Animals↗
PubMed1997

Ultrasound improves electrolytic recovery of metals.

Ultrasound has been shown to improve the cathodic current efficiency of copper electrodeposited from a dilute acidic sulphate bath and also zinc from a dilute alkaline zincate bath. Depending upon the plating parameters the metal may be plated with an enhanced value as a foil, sheet or powder. This agitation may be utilised in the recovery of metal from waste solutions and also in the recycling of acids and alkalies.

Journal Article↗
PubMed1997

Bioactivation of the mushroom hydrazine, agaritine, to intermediates that bind covalently to proteins and induce mutations in the Ames test.

The present study was undertaken to establish whether liver and kidney enzyme systems, from rat and mouse, have the potential to metabolise and bioactivate agaritine, beta-N-(gamma-L(+)glutamyl)-4-(hydroxymethyl)phenylhydrazine, the most abundant hydrazine present in the edible mushroom Agaricus bisporus. Agaritine was weakly mutagenic, in the absence of an activation system, in Salmonella typhimurium strain TA104. Rat kidney homogenates, characterised by high gamma-glutamyl transpeptidase activity, enhanced the mutagenic response. In contrast, hepatic microsomes, having very low gamma-glutamyl transpeptidase activity, did not influence the mutagenicity of agaritine. However, hepatic microsomes could further potentiate the mutagenic response induced by the kidney. Agaritine was a good substrate for purified gamma-glutamyl transpeptidase, being converted to a major metabolite, 4-(hydroxymethyl)phenylhydrazine, formed as a result of the loss of the glutamyl moiety. Kidney homogenates from the rat and mouse also catalysed this reaction, the former being the more effective. Metabolism of agaritine was suppressed by serine-borate, an inhibitor of gamma-glutamyl transpeptidase. Kidney homogenates from rat and mouse could metabolise agaritine to intermediate(s) that bound covalently to proteins, with the rat preparations being the more effective; covalent binding was inhibited by glutathione. In contrast, hepatic preparations alone were ineffective in producing such covalent binding but did further increase the covalent binding mediated by the kidney preparations. It is concluded that rat and mouse kidney homogenates catalyse the removal of the glutamyl group from agaritine to yield the reactive free hydrazine, which is further converted to the highly reactive diazonium ion by hepatic microsomes.

Animals↗
PubMed1997

Osteoporosis risk factors in eighth grade students.

This study described the incidence of osteoporosis risk factors and compared gender differences in Midwestern eighth grade students. Non-modifiable risk factors were gender, ethnic heritage, and family history. Modifiable risk factors were calcium intake, physical activity, sodium intake, body mass index (BMI), smoking status, and alcohol intake. One hundred thirty-eight student/ parent pairs were sampled. Descriptive statistics and Chi-square analyses were conducted. The mean student risk factor total was 4.1 for non-modifiable and modifiable (1.9 and 2.3, respectively). Significantly more males had adequate calcium intakes, excessive sodium intakes, and low BMI values. Adolescents with several non-modifiable risk factors in combination with a number of modifiable risk factors may have increased risk for developing osteoporosis by compromising their peak bone mass. Further research should use DEXA analysis for bone density levels to determine if risk factor totals coincided with bone density levels.

Adolescent↗
PubMed1997

Effect of remote distractors on saccade programming: evidence for an extended fixation zone.

In a series of experiments, we examined the increase in saccade latency that is observed consistently when distractor stimuli are presented simultaneously with the saccade target at various nontarget locations. In the first experiment, targets and distractors were presented on the horizontal axis. We found that saccade latency was increased when distractors appeared at fixation and in the contralateral nontarget hemifield (at eccentricities < or = 10 degrees). In contrast, latency was unaffected by distractors presented along the ipsilateral target axis, but amplitude was increased as saccades tended to land at intermediate locations between the two stimuli (global effect). The effect of presenting distractors at various two-dimensional locations in both the target and nontarget hemifields then was examined, and the maximum latency increase again was observed when distractors appeared at fixation. Distractors presented on any of the eight principal axes in either hemifield, other than on the horizontal target axis, also increased latency. The relationship between the effects of distractors on latency and amplitude was reciprocal. Within approximately 20 degrees of the target axis itself, distractors affected saccade amplitude but not latency. In contrast, distractors presented outside this "window" increased saccade latency without affecting amplitude. A systematic quantitative relationship was revealed between the increase in latency and the ratio between target and distractor eccentricities. The latency increase was largest with small values of the ratio and reached a peak with distractors at the fixation location. The finding that the increase observed for more eccentric distractor locations fitted the same function as that at fixation shows that inhibitory effects operate over large areas of the visual field. The increase in latency under distractor conditions is interpreted in light of recent neurophysiological findings of inhibitory processes operating in the rostral region of the superior colliculus. Our results suggest that these inhibitory processes are not restricted to the central foveal region alone but operate over wider regions of the visual field.

Adult↗
PubMed1997

Recognizable magnetic resonance imaging characteristics of intramuscular myxoma.

Extremity intramuscular myxoma is an uncommon, deep, benign soft-tissue neoplasm. It is characterized clinically by slow growth and minimal symptoms. Resection achieving wide surgical margins is curative. This article presents the imaging characteristics of five extremity intramuscular myxomas. Images of this benign neoplasm, especially magnetic resonance imaging, are characteristic enough for preoperative recognition. This knowledge can facilitate treatment by avoiding biopsy, permitting primary myectomy, and assisting the pathologist in diagnosing a neoplasm that frequently has overlapping histologic characteristics with other soft-tissue tumors.

Adult↗