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Biomedical subjects

D A Jackson

Publications and source records attributed to D A Jackson.

At least 19 recordsLinked to original sources
PubMed1992

Mortality and occupational exposure to radiation: first analysis of the National Registry for Radiation Workers.

OBJECTIVE: To study cause specific mortality of radiation workers with particular reference to associations between fatal neoplasms and level of exposure to radiation. DESIGN: Cohort study. SETTING: United Kingdom. SUBJECTS: 95,217 radiation workers at major sites of the nuclear industry. MAIN OUTCOME MEASURE: Cause of death. RESULTS: Most standardised mortality ratios were below 100: 83 unlagged, 85 with a 10 year lag for all causes; 84 unlagged, 86 lagged for all cancers; and 80 for all known other causes, indicating a "healthy worker effect." The deficit of lung cancer (75 unlagged, 76 lagged) was significant at the 0.1% level. Standardised mortality ratios were significantly raised (214 unlagged, 303 lagged) for thyroid cancer, but there was no evidence for any trend with external recorded radiation dose. Dose of external radiation and mortality from all cancers were weakly correlated (p = 0.10), and multiple myeloma was more strongly correlated (p = 0.06); for leukaemia, excluding chronic lymphatic, the trend was significant (p = 0.03; all tests one tailed). The central estimates of lifetime risk derived from these data were 10.0% per Sv (90% confidence interval less than 0 to 24%) for all cancers and 0.76% per Sv (0.07 to 2.4%) for leukaemia (excluding chronic lymphatic leukaemia). These are, respectively, 2.5 times and 1.9 times the risk estimates recommended by the International Commission on Radiological Protection, but 90% confidence intervals are large and the commission's risk factors fall well within the range. The positive trend with dose for all cancers, from which the risk estimate was derived, was not significant. The positive association between leukaemia (except chronic lymphatic leukaemia) was significant and robust in subsidiary analyses. This study showed no association between radiation exposure and prostatic cancer. CONCLUSION: There is evidence for an association between radiation exposure and mortality from cancer, in particular leukaemia (excluding chronic lymphatic leukaemia) and multiple myeloma, although mortality from these diseases in the study population overall was below that in the general population. The central estimates of risk from this study lie above the most recent estimates of the International Commission on Radiological Protection for leukaemia (excluding chronic lymphatic leukaemia) and for all malignancies. However, the commission's risk estimates are well within the 90% confidence intervals from this study. Analysis of combined cohorts of radiation workers in the United States indicated lower risk estimates than the commission recommends, and when the American data are combined with our analysis the overall risks are close to those estimated by the commission. This first analysis of the National Registry for Radiation Workers does not provide sufficient evidence to justify a revision in risk estimates for radiological protection purposes.

Adult↗
PubMed1992

The attachments of chromatin loops to the nucleoskeleton.

It is widely assumed by cell biologists that chromatin is looped by attachment to some nuclear skeleton. 'Structural' attachments might be mediated through specific sequences; these would be attached in most cells in an organism, underlying the basic structure of the mitotic chromosome and persisting throughout interphase. 'Functional' attachments might also exist, perhaps if active polymerases are attached to the skeleton and replication and transcription occur as DNA is reeled through them. Cells of different tissues--and even cells of the same tissue--would have different attachments of this type. Problems associated with demonstrating these two kinds of attachment are discussed. We find little good evidence for 'structural' attachments and explore the idea that 'functional' attachments are the only kind that exist: 'functional' attachments involving active transcription units might be stable enough to organize chromatin during both interphase and mitosis, but 'dynamic' enough to allow duplication of attached sequences without disrupting loops.

Animals↗
PubMed1992

Weaning practices and breast-feeding duration in Northern Thailand.

Current infant feeding guidelines recommend exclusive breast-feeding until the infant is about 4 months old to reduce the risks of early termination of breast-feeding, undernutrition and infection. In many societies, however, supplementary foods are given well before 4 months of age. The present paper describes weaning practices, factors associated with early supplementation and the effects of supplementation on duration of breast-feeding in a random sample of sixty northern Thai breast-fed infants studied prospectively from birth to 2 years of age. Composition of supplementary foods, energy and protein intake from supplements and changes in the supplementary diet with increasing infant age are also described. Rice-based foods were given from soon after birth; 81% of the sample had received supplements by 6 weeks of age. Early supplementary feeding was significantly associated with rural residence, large household size, maternal employment in agriculture and maternal age. Girls and infants with lower birth weights tended to be supplemented earlier. Despite early feeding of supplements, breast-feeding was prolonged, with median duration of 12 months. Early introduction of supplements and quantity of supplements consumed in the first 3 months were not associated with duration of breast-feeding. However, mothers who gave infant formula as the first supplementary food stopped breast-feeding slightly earlier, as did younger mothers living in households with more children.

Breast Feeding↗
PubMed1992

Acetylcholine synthesis and release is enhanced by dibutyryl cyclic AMP in a neuronal cell line derived from mouse septum.

Cholinergic properties of the SN56.B5.G4 cell line derived from the fusion of neurons of the mouse postnatal day 21 septum and the murine neuroblastoma cell line N18TG2 were investigated and correlated with morphological differentiation. In basal serum-containing growth medium, few cells developed neurites. Neurite extension occurred in cells grown for 2 d with forskolin or dibutyryl cAMP (dbcAMP) but not with butyrate. In cells treated with these compounds, the activity of ChAT and ACh content were two- to threefold higher relative to controls. The cells synthesized ACh from choline taken up by the sodium-dependent high-affinity transport. Forskolin-, dbcAMP-, and butyrate-treated cells (but not the controls) were capable of spontaneous and depolarization-evoked ACh release. The results indicate that the morphological and the neurochemical aspects of SN56.B5.G4 cell differentiation are independently regulated.

Acetylcholine↗
PubMed1992

Ectopic pregnancy: a case study.

Ectopic pregnancy occurs when a fertilized egg implants on tissue other than the lining of the uterus. As the number of ectopic pregnancies increase, it is important that PACU nurses understand postoperative assessment and interventions for these women. Hypovolemic shock from preoperative and intraoperative bleeding is one potential problem for these patients that requires close postoperative monitoring. The case study of the ectopic pregnancy patient included with this article demonstrates important postanesthesia assessment parameters.

Adult↗
PubMed1991

Structure-function relationships in eukaryotic nuclei.

It may be that eukaryotic nuclei contain a collection of operationally independent units (genes), each controlled through its interactions with soluble protein factors which diffuse at random throughout the nucleoplasmic space. Alternatively, nuclei might be organized in such a sophisticated fashion that specific genes occupy distinct sites and that spatially ordered RNA synthesis, processing and transport delivers mature RNAs to predestined sites in the cytoplasm. Different fields of research support each of these extreme views. Molecular biologists inspecting the precise details of specific interactions, usually in vitro, inevitably favour the former, while cell biologists working with far more complicated systems generally assume that more elaborate arrangements exist. In considering the importance of nuclear architecture, I have attempted to relate a collection of experiments each of which intimates some close relationship between structural aspects of chromatin organization and the precise mechanisms underlying nuclear function. I will argue that higher-order structures are crucial for achieving the observed efficiency and coordination of many nuclear processes.

Animals↗
PubMed1991

Successful sustained lactation following postpartum tubal ligation.

This study was undertaken to see whether tubal ligation performed within days postpartum, and associated with a delay in the initiation of breastfeeding, exerts a disruptive influence on successfully establishing lactation among the rural population of northern Thailand. Lactational performance of 12 rural northern Thai mothers was not affected by the delay in reunion of mothers with their babies as a result of postpartum tubal sterilization procedure when compared with a group of 8 other healthy mothers and babies. The volume of breast milk transferred, frequency of breastfeeding and the total feeding time spent on the breast were similar on days 15, 45, 90, 180 and 360 postpartum. This finding suggests that the pattern of intense breastfeeding activity as practiced by this group of mothers has a stronger influence on prolonged and successful lactation than early contact in the immediate postpartum period.

Adult↗
PubMed1991

The extracellular matrix coordinately modulates liver transcription factors and hepatocyte morphology.

The extracellular matrix (ECM) promotes tissue morphogenesis, cell migration, and the differentiation of a variety of cell types. However, the mechanisms by which ECM causes differentiated gene expression have been unknown. In this report, we show that culturing the hepatocyte-derived cell line H2.35 on an ECM gel changes cell morphology and selectively stimulates the transcription of a subset of liver-specific genes, including serum albumin. Transcriptional activation by ECM also occurs with transfected plasmids bearing the transcriptional enhancer of the albumin gene. ECM substrates of different composition activated the albumin enhancer only when the ECM promoted a cuboidal, differentiated cell morphology. Enhancer activation by the ECM was mediated by two liver transcription factors, HNF3 alpha and eH-TF, which appear to be regulated differently by matrix. Specifically, we found that a collagen gel substratum caused a selective increase in the factor HNF3 alpha at the levels of mRNA accumulation and DNA-binding activity in nuclear extracts, both in H2.35 cells and in the hepatoma cell line HepG2. We conclude that the ECM can stimulate cell differentiation by selectively activating transcriptional regulatory factors and that such regulation occurs coordinately with ECM-promoted changes in cell shape.

Albumins↗
PubMed1991

Ranitidine in the treatment of non-steroidal anti-inflammatory drug associated gastric and duodenal ulcers.

In a multicentre study the effect of ranitidine on healing non-steroidal anti-inflammatory drug (NSAID) associated peptic ulcers was compared in a group of patients who had stopped NSAID treatment with another group who continued with NSAID treatment. A total of 190 patients with confirmed ulcers were randomised to continue or stop NSAID treatment. All patients in addition received ranitidine 150 mg twice daily. Patients were endoscopically monitored at four, eight, and 12 weeks. Gastric ulcers at eight weeks had healed in 63% of those taking NSAIDs compared with 95% of those who had stopped NSAID treatment. For duodenal ulcer the healing rates at eight weeks were 84% in the group continuing NSAIDs compared with 100% in those who stopped NSAIDs. The differences in healing rates were statistically significant for both gastric ulcer (p = 0.001) and for duodenal ulcer (p = 0.006). At 12 weeks, 79% of gastric ulcers and 92% of duodenal ulcers were healed in the group continuing with NSAIDs. All patients with gastric and duodenal ulcers who stopped taking NSAIDs were healed at 12 weeks. The study shows that ranitidine 150 mg twice daily effectively heals NSAID associated peptic ulcers. Healing is more successful when NSAID treatment stops but even if these drugs are continued, substantial healing rates are achievable.

Adult↗
PubMed1990

Attachment of DNA to the nucleoskeleton of HeLa cells examined using physiological conditions.

Although it is widely believed that eukaryotic DNA is looped by attachment to a nucleoskeleton, there is controversy about its composition and which sequences are attached to it. As most nuclear derivatives are isolated using unphysiological conditions, the criticism that attachments seen in vitro are generated artifactually has been difficult to rebut. Therefore we have re-investigated attachments of chromatin to the skeleton using physiological conditions. HeLa cells are encapsulated in agarose microbeads and lysed using Triton in a 'physiological' buffer. Then, most chromatin can be electroeluted after treatment with a restriction enzyme to leave some at the base of the loops still attached. Analysis of the size and amounts of these residual fragments indicates that the loops are 80-90kbp long. The residual fragments are stably attached, with about 1kbp of each fragment protected from nuclease attack. This is very much longer than a typical protein-binding site of 10-20bp.

Chromatin↗
PubMed1990

Does butylphenyl-deoxyguanosine triphosphate differentially inhibit DNA polymerase alpha and delta activities in permeabilized HeLa cells?

In eukaryotic cells, two enzymes, DNA polymerases alpha and delta, are thought to play major roles in DNA synthesis. I have used butylphenyl dGTP (BuPdGTP), a potent inhibitor of purified DNA polymerase alpha, to assess the relative activities of these enzymes in two permeabilized cell systems. In both instances BuPdGTP eliminated all of the activity which was sensitive to aphidicolin. However, no conditions were found where BuPdGTP preferentially inhibited the synthesis of Okazaki fragments--the presumed products of DNA polymerase alpha activity. This implies that DNA polymerase activities on the two sides of the replication fork are unable to operate independently, being just two elements of the integrated replication machinery that undertakes DNA synthesis in permeabilized cells.

Cell Membrane Permeability↗
PubMed1990

Active RNA polymerase I is fixed within the nucleus of HeLa cells.

We have investigated whether active RNA polymerase I, the enzyme responsible for transcribing ribosomal RNA, is immobilized by attachment to a large subnuclear structure in HeLa cells. As unphysiological salt concentrations induce artifacts, we have used isotonic conditions throughout the preparative and analytic procedures. Cells are encapsulated in agarose microbeads and lysed in Triton and a 'physiological' buffer; then soluble proteins and RNA diffuse out through the agarose pores to leave encapsulated chromatin. This can be manipulated without aggregation but is accessible to molecular probes; it retains the replicational and transcriptional activities of the living cell. After treatment with a restriction endonuclease, most chromatin can be removed from beads by electrophoresis: then active ribosomal genes and polymerase I remain behind. Active ribosomal genes are very accessible to nuclease digestion whilst the rest are even more inaccessible than inactive globin genes. Our observations confirm the complex organization of rDNA within nucleoli and are compatible with transcription occurring at fixed sites. A model for transcription involving an attached polymerase is presented.

Cell Nucleus↗
PubMed1990

The size of chromatin loops in HeLa cells.

It is widely believed that the chromatin fibre is organized into loops during interphase, with the loop being implicated as an important unit of nuclear function. However, there remains little direct evidence for looping, with estimates of loop size varying widely. This has led to the suggestion that some loops, or even all of them, arise artefactually during isolation as chromatin aggregates so easily. We have now investigated the effect of isolation procedure on loop size using HeLa cells encapsulated in agarose to allow easy manipulation. Loop size in various derivatives (i.e. nuclei, nucleoids, matrices and scaffolds) critically depended on procedure; some (or all) of their loops are artefacts. The loop size in derivatives isolated using the most 'physiological' conditions was 86 kb; this remained unchanged throughout the cell cycle. This loop size is probably an average of a range of loops of between 5 and 200 kb.

Cell Cycle↗
PubMed1990

Receptor subtypes mediating facilitation by serotonin of excitability of spinal motoneurons.

Serotonin receptor ligands, with differential affinity for subtypes of serotonin (5-HT) receptors, were administered intravenously or iontophoretically to urethane-anesthetized rats and the effects of these compounds on glutamate-evoked firing of spinal motoneurons were tested. The excitability of spinal motoneurons was markedly enhanced after intravenous administration of the selective 5-HT1A ligand 8-hydroxy-2-(di-n-propylamino) tetralin (DPAT) in rats with acute spinal transections at C1. However, local application of DPAT, directly into the ventral horn by microiontophoresis, inhibited the glutamate-evoked firing of motoneurons in direct contrast to the facilitatory effects of iontophoretically applied 5-HT. The DPAT-induced inhibition may have been nonspecific, since it was not antagonized by methysergide. Other 5-HT agonists, with relatively selective affinity for 5-HT1B, 5-HT1C and 5-HT2 receptors, increased the excitability of spinal motoneurons when applied iontophoretically or intravenously. The excitatory effect of iontophoretically applied 5-HT was antagonized by the nonselective 5-HT antagonist, methysergide and by ketanserin and ritanserin, which have relatively selective affinity for 5-HT1C and 5-HT2 receptors. These results indicate that 5-HT1A receptors do not mediate facilitation of excitability of motoneurons produced by local application of 5-HT directly into the vicinity of the motoneurons. However, the marked increase in firing of motoneurons that was caused by intravenous administration of DPAT in spinal transected rats, suggests that 5-HT1A receptors in the spinal cord may participate in 5-HT-induced enhancement of somatomotor outflow, at sites presynaptic to the motoneurons. The iontophoretic results suggest that 5-HT1B, 5-HT1C and 5-HT2 receptors may all play a role in facilitation of the excitability of spinal motoneurons by locally applied 5-HT. Differentiation between these subtypes of receptor awaits the development of more completely selective agonists and antagonists.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1990

Roy in the postanesthesia care unit.

The adaptation model developed by Sister Callista Roy, RN, PhD, was used as the organizing framework for developing a preoperative assessment tool for PACU nurses. The purpose of preoperative assessment of a surgical patient by a PACU nurse is to determine the patient's location on the health-illness continuum. This is done by analyzing data regarding the patient's biopsychosocial needs, evaluating the data, and determining from that information what problems need intervention. Roy's theory advocates assessing the patient's biopsychosocial needs using four different adaptive modes: self-concept, physiological function, role function, and interdependence (level I assessment). After completing the PACU preoperative assessment tool, each mode in level I assessment is identified as either positive (adaptive) or negative (maladaptive) depending on the patient's behavior identified by the tool. If a maladaptive behavior is identified during the preoperative assessment, a level II assessment is made to collect data regarding focal, contextual, and residual stimuli. A nursing diagnosis, expected outcomes, nursing interventions, and evaluation are listed on the patient care plan based on the data obtained from the assessment.

Adaptation, Biological↗
PubMed1989

Relationships between nursing patterns, supplementary food intake and breast-milk intake in a rural Thai population.

Relationships between nursing patterns, supplementary food intake and breast-milk intake were examined in a group of 52 Thai babies under 1 year of age. All data were collected over two consecutive days, 24 h/day. Total sucking time (min/day) and supplementary food intake (kcal/day) were significant predictors of breast-milk intake after allowing for the age of the baby: R-squared is 0.32 for sucking time and 0.39 for supplementary food intake. The two variables were themselves correlated (r is -0.47). The number of breastfeeds per day and their mean duration was determined for each case, counting each episode of attachment to the breast as a separate feed. Number and mean duration of breastfeeds were then evaluated as predictor variables. The duration of feeds had no predictive power. Number of feeds was linearly related to milk intake and combined with age was as good a predictor of milk intake as total sucking time (with R-squared 0.34). These results suggest that a simple count of breastfeeds is as valuable as more complex measures of sucking duration in predicting to breast-milk intake.

Breast Feeding↗