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E Parker

Publications and source records attributed to E Parker.

At least 19 recordsLinked to original sources
PubMed1992

Predicting the time of occurrence of decompression sickness.

Probabilistic models and maximum likelihood estimation have been used to predict the occurrence of decompression sickness (DCS). We indicate a means of extending the maximum likelihood parameter estimation procedure to make use of knowledge of the time at which DCS occurs. Two models were compared in fitting a data set of nearly 1,000 exposures, in which greater than 50 cases of DCS have known times of symptom onset. The additional information provided by the time at which DCS occurred gave us better estimates of model parameters. It was also possible to discriminate between good models, which predict both the occurrence of DCS and the time at which symptoms occur, and poorer models, which may predict only the overall occurrence. The refined models may be useful in new applications for customizing decompression strategies during complex dives involving various times at several different depths. Conditional probabilities of DCS for such dives may be reckoned as the dive is taking place and the decompression strategy adjusted to circumstance. Some of the mechanistic implications and the assumptions needed for safe application of decompression strategies on the basis of conditional probabilities are discussed.

Decompression Sickness↗
PubMed1991

Cross-resistance of an amsacrine-resistant human leukemia line to topoisomerase II reactive DNA intercalating agents. Evidence for two topoisomerase II directed drug actions.

HL-60/AMSA is a human leukemia cell line that is 50-100-fold more resistant than its drug-sensitive HL-60 parent line to the cytotoxic actions of the DNA intercalator amsacrine (m-AMSA). HL-60/AMSA topoisomerase II is also resistant to the inhibitory actions of m-AMSA. HL-60/AMSA cells and topoisomerase II are cross-resistant to anthracycline and ellipticine intercalators but relatively sensitive to the nonintercalating topoisomerase II reactive epipodophyllotoxin etoposide. We now demonstrate that HL-60/AMSA and its topoisomerase II are cross-resistant to the DNA intercalators mitoxantrone and amonafide, thus strongly indicating that HL-60/AMSA and its topoisomerase II are resistant to topoisomerase II reactive intercalators but not to nonintercalators. At high concentrations, mitoxantrone and amonafide were also found to inhibit their own, m-AMSA's, and etoposide's abilities to stabilize topoisomerase II-DNA complexes. This appears to be due to the ability of these concentrations of mitoxantrone and amonafide to inhibit topoisomerase II mediated DNA strand passage at a point in the topoisomerization cycle prior to the acquisition of the enzyme-DNA configuration that yields DNA cleavage and topoisomerase II-DNA cross-links. In addition, amonafide can inhibit the cytotoxic actions of m-AMSA and etoposide. Taken together, these results suggest that the cytotoxicity of m-AMSA and etoposide is initiated primarily by the stabilization of the topoisomerase II-DNA complex. Other topoisomerase II reactive drugs may inhibit the enzyme at other steps in the topoisomerization cycle, particularly at elevated concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Amsacrine↗
PubMed1990

HT1080/DR4: a P-glycoprotein-negative human fibrosarcoma cell line exhibiting resistance to topoisomerase II-reactive drugs despite the presence of a drug-sensitive topoisomerase II.

HT1080/DR4 (DR4) is a doxorubicin-resistant human fibrosarcoma line that exhibits 150-fold cross-resistance to etoposide but does not overexpress P-glycoprotein (one mechanism of multiple drug resistance). We examined another possible mechanism that could explain resistance to both doxorubicin and etoposide: a quantitative or qualitative alteration in topoisomerase II, the putative nuclear target of these agents. The amount of immunoreactive topoisomerase II present in whole-cell lysates and nuclear extracts was three- to 10-fold lower in DR4 than in HT1080 cells. However, the topoisomerase II in nuclear extracts from both lines was sensitive to the effects of amsacrine (AMSA) and etoposide. Following treatment with AMSA, etoposide, and 5-iminodaunorubicin, topoisomerase II-mediated DNA cleavage in DR4 cells and nuclei was reduced compared with cleavage in HT1080 parent cells and nuclei. The difference between the HT1080 and DR4 lines in AMSA- and 5-iminodaunorubicin-induced cleavage was similar in cells and nuclei and could be due to the lower amount of DR4 topoisomerase II. By contrast, the difference between the HT1080 and DR4 lines in etoposide-induced DNA cleavage was much greater in cells than in nuclei. This finding suggested that cytosolic factors, removed from isolated nuclei, could influence the susceptibility of intact cells to the cytotoxic and DNA-cleaving actions of etoposide. The specific activities of several antioxidant enzymes, components of the cell's defense against free-radical damage that may be produced by doxorubicin or etoposide, were significantly different in HT1080 and DR4 cytosolic extracts. These differences may constitute an additional mechanism of resistance. Regardless, the magnitude of the resistance of DR4 to doxorubicin and etoposide cannot be explained solely on the basis of a topoisomerase II-related mechanism.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Characterization of an amsacrine-resistant line of human leukemia cells. Evidence for a drug-resistant form of topoisomerase II.

HL-60/AMSA is a human leukemia cell line that is 100 times more resistant to the cytotoxic actions of the antineoplastic, topoisomerase II-reactive DNA intercalating acridine derivative amsacrine (m-AMSA) than is its parent HL-60 line. HL-60/AMSA cells are minimally resistant to etoposide, a topoisomerase II-reactive drug that does not intercalate. Previously we showed that HL-60 topoisomerase II activity in cells, nuclei, or nuclear extracts was sensitive to m-AMSA and etoposide, while HL-60/AMSA topoisomerase II was resistant to m-AMSA but sensitive to etoposide. Now we show that purified topoisomerase II from the two cell lines exhibits the same drug sensitivity or resistance as that in the nuclear extracts although the magnitude of the m-AMSA resistance of HL-60/AMSA topoisomerase II in vitro is not as great as the resistance of the intact HL-60/AMSA cells. In addition HL-60/AMSA cells are cross-resistant to topoisomerase II-reactive intercalators from the anthracycline and ellipticine families and the pattern of sensitivity or resistance to the cytotoxic actions of the various topoisomerase II-reactive drugs is paralleled by topoisomerase II-reactive drug-induced DNA cleavage and protein cross-link production in cells and the production of drug-induced, topoisomerase II-mediated DNA cleavage and protein cross-linking in isolated biochemical systems. In addition to its lowered sensitivity to intercalators, HL-60/AMSA differed from HL-60 in 1) the susceptibility of its topoisomerase II to stimulation of DNA topoisomerase II complex formation by ATP, 2) the catalytic activity of its topoisomerase II in an ionic environment chosen to reproduce the environment found within the living cell, and 3) the observed restriction enzyme pattern on a Southern blot probed with a cDNA for human topoisomerase II. These data indicate that an m-AMSA-resistant form of topoisomerase II contributes to the resistance of HL-60/AMSA to m-AMSA and to other topoisomerase II-reactive DNA intercalating agents. The drug resistance is associated with additional biochemical and molecular alterations that may be important determinants of cellular sensitivity or resistance to topoisomerase II-reactive drugs.

Adenosine Triphosphate↗
PubMed1989

[Professional role of the physician in health care].

The professional role of the doctor in health care was analyzed in terms of the peculiarities of the chilean social reality. Determining factors include tradition, the expectations of society and demands of health policies. Action fields and primary and delegated functions are identified. This may be important to help prevent the take over of some of these functions by other health professionals.

Chile↗
PubMed1988

Preadmission screening: an efficacy study.

The effectiveness of hospital social work preadmission screening and assessment is compared with postadmission screening and assessment. Outcome variables include length of stay, readmission rates, posthospital home management, resource attainment, and satisfaction with hospital services. The patients screened postadmission were assessed within forty-eight hours of admission, while the patients screened preadmission were assessed one to two weeks prior to admission. Telephone follow-up was conducted with both groups. Preadmission patients reported better home management and attained more resources. Patients' satisfaction with hospital care was inversely related to the need for more resources in the post-hospital period.

Aged↗
PubMed1987

Pharmacological evaluation of an intra-oral fluoride-releasing device in adolescents.

The purpose of this study was to quantify fluoride (F) concentrations in body fluids of adolescents wearing two intra-oral fluoride-releasing devices (IFRDs) designed to release 0.10 mg F/day. Fluoride concentrations were determined potentiometrically. No significant increases occurred in urine or serum F concentrations during the 26-week device phase. Elevated salivary F concentrations were maintained throughout the device phase when broken or depleted IFRDs were replaced. However, salivary F concentrations returned to pre-device phase values by 26 weeks when the original IFRDs were maintained. These findings suggest that IFRDs can significantly elevate salivary F concentrations of adolescents without significant elevations in systemic F concentrations.

Adolescent↗
PubMed1987

Detention in Broadmoor. Factors in length of stay.

When the length of stay of restricted patients admitted to Broadmoor under the legal category of psychopathic disorder was examined, the factor found to be of primary importance was the gravity of the admission offence. If the men's offences did not cause personal injury, they had a good chance of early release. Patients convicted of violent or sexual offences, and particularly those who attacked strangers, made up the great majority of the long-term group. For the mentally ill there was no relationship between length of stay and admission offence: instead the data suggested that severity and chronicity of illness were the main relevant factors.

Antisocial Personality Disorder↗