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Biomedical subjects

M C Davis

Publications and source records attributed to M C Davis.

At least 19 recordsLinked to original sources
PubMed2000

The role of stressful events in the relationship between positive and negative affects: evidence from field and experimental studies.

Three studies are presented that examine the effects of stress on the relationship between positive and negative affective states. In the first study, recently bereaved and disabled older adults were compared to matched control groups without these recent stressors. Negative affect was inversely correlated with positive affect to a significantly greater extent for the highly stressed groups compared with controls. In a second study, older adults were exposed to a laboratory stressor, and their positive and negative affective reactions recorded. Immediately following a speech stressor task, the inverse correlation between positive and negative affect was significantly greater than in pre- and postassessments of affects. The third study was an attempt to replicate and extend the findings from Study 2 with a mid-aged sample of women. The speech stressor had the same effects as in Study 2. A second stressor, which induced pain through immersion of an arm into cold water, had no effects on the correlation between affective states. Alternative explanations for these effects and the implications for cognitive interventions are discussed.

Adult↗
PubMed1999

Oral contraceptive use and hemodynamic, lipid, and fibrinogen responses to smoking and stress in women.

The effects of acute smoking and oral contraceptive (OC) use on cardiovascular, lipid, and fibrinogen stress responses were examined in 52 female smokers and nonsmokers, half of whom were using OCs. Women smoked or sham-smoked a cigarette and then performed 2 stressful tasks. Stress elicited increases in total and low-density lipoprotein cholesterol, and in triglycerides among women who smoked, and in fibrinogen among all women. Smokers who used OCs had greater blood pressure increases to smoking and to stress than did smokers who did not use OCs. OC use was also associated with enhanced total peripheral resistance stress responses among women who smoked and cardiac output stress responses among women who sham-smoked. Results suggest that OC use moderates cardiovascular reactivity in smokers but not nonsmokers, enhancing vascular responsivity to smoking combined with stress and myocardial responsivity to stress alone.

Adolescent↗
PubMed1999

Association of negative and positive social ties with fibrinogen levels in young women.

The associations between positive and negative aspects of social relationships and fibrinogen, a risk factor for coronary heart disease (CHD), were examined in young, healthy women recruited from the community (n = 46) and from a college campus (n = 42). For community women, the perception that individuals in their social networks frequently undermined them was related to higher fibrinogen, independent of perceived frequency of support. For college women, fibrinogen was elevated among women with frequent undermining only when they also reported infrequent support. After controlling for other risk factors, the associations between social ties and fibrinogen remained significant in both samples. These results indicate that positive and negative social ties are associated with fibrinogen levels and suggest that social relationships may affect CHD risk in part through their influence on fibrinogen.

Adult↗
PubMed1999

Body fat distribution and hemodynamic stress responses in premenopausal obese women: a preliminary study.

To examine the relationship between body fat distribution and hemodynamic stress responses, cardiovascular responses to a speech task and a forehead cold pressor task were evaluated with 24 premenopausal women classified a priori as either centrally or peripherally obese. Results showed that women with central adiposity exhibited greater stress-related increases in diastolic blood pressure and total peripheral resistance, whereas women with peripheral adiposity exhibited greater stress-related increases in cardiac output. Depression, self-consciousness, hostility, and mood scores did not explain significant variance in the stress response differences between regional adiposity groups. The findings suggest that central adiposity may increase the risk of cardiovascular disease in women at least in part by enhancing vascular responses to stress.

Adipose Tissue↗
PubMed1998

Antimycobacterial activity of substituted isosteres of pyridine- and pyrazinecarboxylic acids.

Pyrazines and pyridines substituted with alkylated tetrazoles, esterified vinylogous carboxylic acids, and ketosulfides were synthesized as precursors of antimycobacterial agents which, after penetration of the mycobacterial cell wall, could be biotransformed by esterases or peroxidase-catalases. The expected products are tetrazoles, a vinylogous carboxylic acid, and CH-acidic ketosulfoxides, isosteres of pyrazinoic and nicotinic acids, which should inhibit mycobacterial growth when released inside the bacterial cell. The growth inhibitory activity of the synthesized compounds against the H37Rv strain of Mycobacterium tuberculosis was determined to assess the viability of this concept. It was shown that all of the compounds designed as lipophilic precursors were more active than the unmodified polar isosteres of pyrazinoic and nicotinic acids.

Antitubercular Agents↗
PubMed1998

MR teleradiology network serving remote imaging centers.

The operational experience of a commercial teleradiology practice utilizing a wide-area ISDN network linking six imaging centers located in two states will be reviewed. Open magnet designs were chosen to complement existing high-field units available in each community. Image data was first acquired than transmitted without compression at 128 Kbytes/s to a central reading site located in McLean, Virginia for interpretation by a team of radiologists. Average transmission time was 6-8 minutes. System design allows optimal utilization of radiologists expertise in imaging interpretation while reserving the on-site patient management responsibilities such as gadolinium contrast injections and sedation to a nonradiologists physician and/or nurse practitioner. Over 15,000 teleradiology readings have been rendered via this network by January 1998.

Adult↗
PubMed1998

Use of combinatorial library screening to identify inhibitors of a bacterial two-component signal transduction kinase.

Bacterial resistance to antibiotics is emerging as a major concern to the medical community. The appearance of several antibiotic-resistant strains, including multidrug-resistant Staphylococcus aureus, raises the prospect that infections by these bacteria could soon become untreatable with currently available antibiotics. In order to address this problem, increased emphasis is being placed on the discovery of novel classes of antibacterial agents that inhibit novel molecular targets using sources of compounds not yet exploited for antibiotic drug discovery. Novel classes of compounds can now be rapidly investigated using combinatorial chemistry approaches. This report describes the identification of novel antibacterial compounds from a combinatorial library of N-acetylated, C-amidated D-amino acid hexapeptides. This library of compounds was screened for inhibitors of CheA, a member of the bacterial two-component signal transduction kinase family. Several peptides with apparent IC50 values in the low micromolar range were identified. In addition to inhibiting CheA, these peptides inhibited mammalian protein kinase C (from rat brain) with comparable potency. Finally, these peptides were also found to have significant antibacterial properties, although the true mechanism by which they exhibited inhibition of bacterial growth remains uncertain.

Amino Acids↗
PubMed1997

Effect of prior nicotine treatment on drug induced changes in serum LH concentrations in rats.

The effect of daily injections of nicotine on drug induced changes in LH secretion was investigated in male rats. Daily administration of nicotine for 7 days resulted in decreased basal serum LH concentrations. Nicotine treatment blocked naloxone induced LH release and reduced LHRH induced increases in serum LH. Clonidine induced increases in serum LH were not altered by nicotine treatment and haloperidol treatment did not alter nicotine induced decreases in serum LH. In an acute study nicotine blocked LH secretion induced by the long acting opioid antagonist naltrexone. Collectively these results indicate that opioidergic neurons are involved in the reduction in serum LH that occurs following nicotine. They also indicate that chronic nicotine treatment can reduce the pituitary gland response to LHRH.

Adrenergic alpha-Agonists↗
PubMed1997

Teleradiology in rural imaging centres.

An economic analysis of a private commercial magnetic resonance (MR) imaging service was carried out. At an expected case-load of 2000 per year, a mid-field MR unit was predicted to cost $470 per case using teleradiology and $544 per case using film and a courier service. Routine and emergency MR services were provided to two communities in Maryland. In a two-year study period, 8083 teleradiology examinations were performed. Digital images were acquired and transmitted without data compression via ISDN at 128 kbit/s to a central diagnostic workstation for interpretation by a team of radiologists. The average transmission time for a typical case of 50 images was 6-8 min. Preliminary interpretations were normally available within 2 h and the final transcribed reports were usually faxed to the physicians' offices within 24 h. The results of a survey indicated that the system was well received by both referring physicians and patients. Costs per case in practice were similar to those predicted.

Feasibility Studies↗
PubMed1997

Thermo Sequenase DNA polymerase and T. acidophilum pyrophosphatase: new thermostable enzymes for DNA sequencing.

A combination of thermostable enzymes has been developed that produces higher quality cycle sequences. Thermo Sequenase DNA polymerase is a thermostable enzyme engineered to catalyze the incorporation of ddNTPs with an efficiency several thousandfold better than other thermostable DNA polymerases. Since the enzyme also catalyzes pyrophosphorolysis at dideoxy termini, a thermostable inorganic pyrophosphatase is needed to remove the pyrophosphate produced during sequencing reactions. Thermoplasma acidophilum inorganic pyrophosphatase (TAP) is thermostable and effective for converting pyrophosphate to orthophosphate. The use of the combination of Thermo Sequenase polymerase and TAP for cycle sequencing yields sequence data with uniform band intensities, allowing the determination of longer, more accurate sequence reads. Uniform band intensities also facilitate interpretation of sequence anomalies and the presence of mixed templates. Sequencing PCR products of DNA amplified from heterozygous diploid individuals results in signals of equal intensity from each allele.

Cloning, Molecular↗
PubMed1996

Family behavior, adaptation, and treatment adherence of pediatric nephrology patients.

In this exploratory study we investigated the relationships among family behavior variables (e.g., family expressiveness), adaptive functioning skills, maladaptive behavior, and adherence to treatment in pediatric renal failure patients. The study included 22 pediatric outpatients with renal failure who had not yet received dialysis or transplantation (RF) and their parents, and 12 pediatric outpatients with kidney transplants (TX) and their parents. For the RF patients, significant correlations were found between some of their adaptive functioning skills and measures of their medication adherence, diet adherence, and clinic appointment adherence; however, for the TX patients significant correlations were found only between some of their adaptive functioning skills and measures of their medication adherence. For the RF patients only, some measures of their family behavior were significantly correlated with measures of their medication adherence and diet adherence. Additionally, some measures of the RF patients' family behavior were significantly related to their communication skills, socialization skills, overall adaptive functioning skills, and maladaptive behavior. For the TX patients, only their socialization skill level was significantly correlated with one measure of their family behavior. It is concluded that facilitation of adaptive and physical functioning among renal pediatric patients likely requires multidimensional training and/or counselling interventions with the children and their families, and that some of the content and/or emphasis of this training likely needs to differ for RF patients versus TX patients.

Adaptation, Psychological↗
PubMed1996

Do gender-relevant characteristics determine cardiovascular reactivity? Match versus mismatch of traits and situation.

This study tested the hypothesis that individuals exhibit heightened cardiovascular reactivity to a challenging task that is consistent vs. inconsistent with their gender-relevant attributes. In all, 82 men and women categorized as either highly instrumental or expressive engaged in an interpersonal task designed to tap instrumental or expressive characteristics. Results failed to confirm the hypothesis. Expressive individuals tended to exhibit larger increases in systolic blood pressure during an instrumental, relative to an expressive, interaction. Instrumental individuals tended to show larger increases in diastolic blood pressure during an expressive, relative to an instrumental, interaction. These results are consistent with the post hoc interpretation that environmental demands that fall outside of one's perceived areas of competency may result in exaggerated cardiovascular responsivity.

Adolescent↗
PubMed1995

Are job characteristics related to fibrinogen levels in middle-aged women?

This study examined whether employment status or job characteristics thought to be stressful were related to fibrinogen level in a sample of 161 healthy middle-aged women. Employed women had higher fibrinogen levels than did nonemployed women. Moreover, among employed women, those who perceived high levels of job stress or low support from their bosses had elevated fibrinogen, independent of menopausal status. Perception of low support from one's boss was related to higher fibrinogen levels only among premenopausal women or postmenopausal women who were not using hormone replacement therapy. These results are consistent with the notion that stress associated with some job characteristics influences levels of fibrinogen in women.

Adult↗
PubMed1995

Effects of nullisomic chromosome deficiencies on conjugation events in Tetrahymena thermophila: insufficiency of the parental macronucleus to direct postzygotic development.

Conjugation fails postzygotically after mating of Tetrahymena cells that have wild-type parental macronuclei but harbor noncomplementing nullisomic parental germline deficiencies. Failures begin shortly after formation of the new macronuclear precursor (anlage) and completion of the first step in elimination of the parental macronucleus (pycnosis). Conjugants fail to complete pair separation, to eliminate one new micronucleus, and to amplify anlage DNA, and they eventually die. Some deficiencies block resorption of the pycnotic parental macronucleus, but we find no evidence for its regeneration. Some deficiencies cause aberrant anlage DNA loss. Those that do not cause DNA loss are epistatic to those that do, indicating that normal anlage development requires the dependent function of at least two types of genes. The possibility that these genes are involved in developmentally regulated anlage DNA rearrangements is discussed. Each observed conjugation defect indicates insufficiency of the parental macronucleus to direct postzygotic development and can be explained by the deficiency of essential conjugation genes that are expressed from the anlage. The failure of nullisomic conjugants to complete pair separation indicates a requirement for gene products, expressed from the early anlage or its precursors, soon after anlage first differentiate.

Animals↗
PubMed1994

Identification of a novel polypeptide involved in the formation of DNA-containing vesicles during macronuclear development in Tetrahymena.

An abundant phosphoprotein with an apparent molecular mass of 65 kDa (p65) has been identified that is enriched in developing new macronuclei (or anlagen) isolated from the holotrichous ciliate, Tetrahymena thermophila. During early stages of macronuclear development, p65 is actively synthesized and deposited into young (4C) anlagen and is not found in micronuclei or parental macronuclei. p65 is not detected in older (8C) anlagen or in vegetatively growing or starved cells, and thus p65 is under stringent developmental control. In situ analyses, using polyclonal antibodies generated against p65, demonstrate that p65 undergoes a pronounced change in distribution during anlagen differentiation. Initially, anlagen are uniformly stained with these antibodies. However, following separation of conjugants, this staining pattern converts to one that is punctate and fragmented. As development proceeds, most, if not all, of these p65-based particles become peripherally located in anlagen and appear as well-defined vesicles surrounding a discrete central core of DNA of yet undetermined origin. This remarkable cytological distribution suggests an involvement of p65 in the elimination or processing of DNA during anlagen differentiation. If the above is correct, p65 provides the first inroad into the protein machinery involved in the well-known DNA rearrangements that characterize ciliate macronuclear development.

Animals↗