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Biomedical subjects

R White

Publications and source records attributed to R White.

At least 55 records · Page 3Linked to original sources
PubMed2001

Benchmarking the endodontic literature on MEDLINE.

The purpose of this study was to identify and quantify the endodontic literature available for clinical decision making. A search strategy based on Medical Subject Headings for endodontics was developed to examine MEDLINE. The identified articles were limited to human subjects and English. Sensitive and specific methodological search filters identified four categories of information: etiology, diagnosis, therapy, and prognosis. The results were then subdivided by year to identify trends. Between 1990 and 1998 MEDLINE identified 3,152 articles published in English on endodontics in humans. The number of articles per year (mean +/- SD) for sensitive and specific searches was etiology (28+/-10, 1+/-2), diagnosis (38+/-11, 1+/-1), therapy (59+/-15, 3+/-3), and prognosis (40+/-13, 10+/-5), respectively. The number of articles in each category increased by 1 to 3% each year. There were 150 articles/yr in endodontics in at least 120 journals cited on MEDLINE on which to base clinical decisions.

Analysis of Variance↗
PubMed2001

High salt intake and the brain renin--angiotensin system in Dahl salt-sensitive rats.

OBJECTIVES: To assess changes in the activity of the brain renin-angiotensin system during (i) the development of salt-sensitive hypertension; and (ii) the prevention of salt-sensitive hypertension by blocking brain 'ouabain'. METHODS: In protocol I, angiotensin converting enzyme (ACE) mRNA and activity and angiotensin I and II levels were assessed in the hypothalamus and pons of Dahl salt-sensitive (Dahl S) and salt-resistant (Dahl R) rats on regular (120 micromol Na+ per g) or high (1370 micromol Na+ per g) salt diet from 4-6 weeks or 4-9 weeks of age. In protocol II, ACE mRNA and activity were assessed in the hypothalamus and pons in Dahl S on regular or high salt treated with intracerebroventricular (i.c.v.) Fab fragments blocking brain 'ouabain' or gamma-globulins, and in Dahl R on high or regular salt ACE mRNA was assessed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay and angiotensin I and II by radioimmunoassay after high-performance liquid chromatography. In protocol III, effects of i.c.v. angiotensin I and i.c.v. bradykinin on renal sympathetic nerve activity (RSNA), heart rate and blood pressure before and after i.c.v. captopril were assessed in Dahl S and R rats on regular or high salt intake from 4-8 weeks of age. RESULTS: High salt diet caused a gradual, but marked increase in blood pressure in Dahl S but not Dahl R rats. Dahl S rats showed small but significant increases in ACE mRNA in the hypothalamus on regular salt diet. In Dahl S rats on high salt diet for 2 or 5 weeks ACE mRNA levels significantly increased in both hypothalamus and pons, compared with Dahl R rats on either diet or Dahl S rats on regular diet. After 5 weeks of high salt diet, ACE mRNA levels in the hypothalamus in Dahl S rats were almost three-fold higher and in the pons two-fold higher than in Dahl R rats on either diet or Dahl S on regular salt diet. High salt diet also increased ACE activity of the hypothalamus and pons in Dahl S but not Dahl R. Consistent with this increased ACE activity, central responses to angiotensin I were clearly enhanced and to bradykinin markedly diminished in Dahl S on high salt intake. Chronic blockade of brain 'ouabain' by i.c.v. Fab fragments prevented the increases in blood pressure, ACE mRNA and activity in the hypothalamus and pons by high salt intake in Dahl S rats. Angiotensin I levels in the hypothalamus and pons were similar in both groups of rats and there were no significant changes caused by high salt diet in Dahl S and R rats. On regular salt intake angiotensin II levels in the hypothalamus of Dahl S rats showed a significant decrease as compared with Dahl R rats on regular salt diet, and were similar in the pons of the two strains. High salt intake did not affect angiotensin II levels in either hypothalamus or pons in Dahl S and R rats. CONCLUSIONS: These results indicate that high salt intake increases blood pressure, ACE expression and activity in the hypothalamus and pons of Dahl S rats without a parallel increase in angiotensin II levels. Effects of high salt intake on ACE mRNA and activity appear to be secondary to activation of brain 'ouabain'.

Angiotensin I↗
PubMed2001

Effect of the blood substitute diaspirin crosslinked hemoglobin in rat mesenteric and human radial collateral arteries.

The actions of the blood substitute diaspirin crosslinked hemoglobin (DCLHb) were investigated in rat (small mesenteric artery) and human (radial collateral artery) resistance vessels mounted in a wire myograph for isometric tension recording. DCLHb did not contract resting vessels from rats, but vasoconstrictor responses were observed in isolated arteries and perfused mesenteric beds prestimulated with threshold concentrations of methoxamine. The DCLHb contractile responses were greatly attenuated by N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) or endothelial removal, whereas BQ-123 (endothelin A receptor antagonist), prazosin (alpha1-adrenoceptor antagonist), or indomethacin (cyclooxygenase inhibitor) had no effect. Endothelium-dependent relaxations to carbachol in both rat mesenteric and human radial collateral artery were inhibited by DCLHb. Relaxations to carbachol were studied in the presence of L-NAME or 25 mM KCl to investigate the effect of DCLHb on endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide, respectively. In both rat and human vessels, EDHF-mediated relaxations were not affected by DCLHb preincubation, whereas the nitric oxide component of carbachol-induced relaxations was practically abolished. In conclusion, inhibition of the effects of basal nitric oxide release underpins the vasoconstrictor effects of DCLHb. DCLHb effectively abolishes the nitric oxide component of carbachol-induced relaxation, with no effect on the EDHF-mediated component in both isolated rat mesenteric and human radial collateral arteries.

Animals↗
PubMed2001

Resistance of Streptococcus pneumoniae to deformylase inhibitors is due to mutations in defB.

Resistance to peptide deformylase inhibitors in Escherichia coli or Staphylococcus aureus is due to inactivation of transformylase activity. Knockout experiments in Streptococcus pneumoniae R6x indicate that the transformylase (fmt) and deformylase (defB) genes are essential and that a def paralog (defA) is not. Actinonin-resistant mutants of S. pneumoniae ATCC 49619 harbor mutations in defB but not in fmt. Reintroduction of the mutated defB gene into wild-type S. pneumoniae R6x recreates the resistance phenotype. The altered enzyme displays decreased sensitivity to actinonin.

Amidohydrolases↗
PubMed2001

Simian immunodeficiency virus replicates to high levels in naturally infected African green monkeys without inducing immunologic or neurologic disease.

African green monkeys can maintain long-term persistent infection with simian immunodeficiency viruses (SIVagm) without developing AIDS and thus provide an important model for understanding mechanisms of natural host resistance to disease. This study assessed the levels and anatomic distribution of SIVagm in healthy, naturally infected monkeys. Quantitative competitive reverse transcriptase PCR assays developed to measure SIVagm from two African green monkey subspecies demonstrated high levels of SIV RNA in plasma (>6 x 10(6) RNA copies/ml) in sabaeus and vervet monkeys. Infectious virus was readily recovered from plasma and peripheral blood mononuclear cells and shown to be highly cytopathic in human cell lines and macrophages. SIVagm DNA levels were highest in the gastrointestinal tract, suggesting that the gut is a major site for SIVagm replication in vivo. Appreciable levels of virus were also found within the brain parenchyma and the cerebrospinal fluid (CSF), with lower levels detected in peripheral blood cells and lymph nodes. Virus isolates from the CSF and brain parenchyma readily infected macrophages in culture, whereas lymph node isolates were more restricted to growth in human T-cell lines. Comparison of env V2-C4 sequences showed extensive amino acid diversity between SIVagm recovered from the central nervous system and that recovered from lymphoid tissues. Homology between brain and CSF viruses, macrophage tropism, and active replication suggest compartmentalization in the central nervous system without associated neuropathology in naturally infected monkeys. These studies provide evidence that the nonpathogenic nature of SIVagm in the natural host can be attributed neither to more effective host control over viral replication nor to differences in the tissue and cell tropism from those for human immunodeficiency virus type 1-infected humans or SIV-infected macaques.

Amino Acid Sequence↗
PubMed2001

Isoproterenol-induced cardiac hypertrophy: role of circulatory versus cardiac renin-angiotensin system.

To assess the possible contribution of the circulatory and cardiac renin-angiotensin system (RAS) to the cardiac hypertrophy induced by a beta-agonist, the present study evaluated the effects of isoproterenol, alone or combined with an angiotensin I-converting enzyme inhibitor or AT(1) receptor blocker, on plasma and LV renin activity, ANG I, and ANG II, as well as left ventricular (LV) and right ventricular (RV) weight. Male Wistar rats received isoproterenol by osmotic minipump subcutaneously and quinapril or losartan once daily by gavage. Plasma and LV ANGs were measured by radioimmunoassay after separation by HPLC. Isoproterenol alone decreased blood pressure, more markedly when combined with losartan or quinapril. Isoproterenol significantly increased LV and RV weight and total collagen. Neither losartan nor quinapril inhibited the increases in LV or RV weight. Losartan prevented the increase in RV collagen but enhanced the increase in LV collagen. Isoproterenol increased plasma renin, ANG I, and ANG II three- to fourfold. Isoproterenol combined with losartan or quinapril, caused marked further increases except for a significant decrease in plasma ANG II with quinapril. Isoproterenol alone did not increase LV ANG II and, combined with losartan or quinapril, actually decreased LV ANG II. These results indicate that isoproterenol-induced cardiac hypertrophy is associated with clear increases in plasma ANG II, but not in LV ANG II. Both losartan and quinapril lower LV ANG II below control levels, but do not prevent the isoproterenol-induced cardiac hypertrophy. These findings do not support a role for the circulatory or cardiac RAS in the cardiac trophic responses to beta-receptor stimulation.

Adrenergic beta-Agonists↗
PubMed2001

Activity and safety of vinorelbine combined with doxorubicin or fluorouracil as first-line therapy in advanced breast cancer: a stratified phase II study.

PURPOSE: To evaluate the efficacy and safety of vinorelbine combined with doxorubicin or continuous infusion of fluorouracil as initial therapy for advanced breast cancer. AUBJECTS AND METHODS: A total of 118 women who had not received chemotherapy for advanced breast cancer were enrolled and included in the intent-to-treat analysis. Subjects were stratified into two treatment groups. If subjects were candidates for anthracycline therapy, they received doxorubicin 50 mg/m(2) on day 1 and vinorelbine 25 mg/m(2) on days 1 and 8 (n = 62). If subjects had received adjuvant anthracycline therapy or had cardiac disease, they received fluorouracil 750 mg/m(2)/day by continuous infusion on days 1 through 5 and vinorelbine 30 mg/m(2) on days 1 and 5 (n = 56). The regimens were repeated every 21 days until evidence of progression of disease or severe toxicity. RESULTS: For doxorubicin and vinorelbine, the objective response rate was 55% (95% confidence interval [CI]: 42% to 68%), median time to disease progression was 34 weeks, median time to treatment failure was 32 weeks, and median survival was 92 weeks (95% CI: 72 to 128 weeks). For fluorouracil and vinorelbine, the objective response rate was 45% (95% CI: 31% to 59%), median time to disease progression was 32 weeks, median time to treatment failure was 30 weeks, and median survival was 53 weeks (95% CI: 47 to 64 weeks). The most common adverse event was grade 3 or 4 granulocytopenia, which occurred in 95% of subjects in the doxorubicin-vinorelbine group and in 88% of those in the fluorouracil-vinorelbine group. The most common nonhematologic adverse event was grade 3 or 4 stomatitis, which occurred in 9% and 32% of subjects in the two groups, respectively. CONCLUSION: Both vinorelbine-containing regimens appear to offer useful options as initial therapy for advanced breast cancer. Both regimens were active, and any efficacy differences between the two may have been related to differences in prognosis for the anthracycline-pretreated group (i.e., selection for prior aggressive adjuvant therapy) and or comorbid cardiac conditions. Both regimens were associated with predictable but manageable toxicity, but a lower dose of fluorouracil (e.g., 600 mg/m(2)/day) should be used to reduce the risk of stomatitis.

Adult↗
PubMed2001

Protein kinase A-dependent and -independent effects of isoproterenol in rat isolated mesenteric artery: interactions with levcromakalim.

The effect of beta-adrenoceptor activation on levcromakalim-induced relaxation was investigated in myograph-mounted rat mesenteric arteries. The nonselective beta-adrenoceptor agonist isoproterenol (at a concentration causing approximately 30% relaxation of methoxamine-induced tone) potentiated relaxation to levcromakalim; higher concentrations exerted no additional effect. The modulatory and relaxant effects of isoproterenol were inhibited by the beta(1)-adrenoceptor antagonist atenolol, but the ATP-sensitive K(+) (K(ATP)) channel inhibitor glibenclamide did not inhibit relaxations to isoproterenol. The protein kinase A inhibitor Rp-adenosine 3',5'-cyclic monophosphothioate triethylamine (Rp-cAMPS) inhibited the ability of isoproterenol to modulate levcromakalim relaxation. However, neither Rp-cAMPS nor N-[2-(p-bromocinnamylamino)ethyl]-6-isoquinolinesulfonamide (H-89) (another protein kinase A inhibitor) markedly reduced isoproterenol-induced relaxation, although Rp-cAMPS inhibited relaxations induced by forskolin (an adenylyl cyclase activator). Iberiotoxin (50 nM), an inhibitor of large conductance Ca(2+)-activated K(+) channels (BK(Ca)), attenuated isoproterenol relaxation. Moreover, both Rp-cAMPS and H-89 caused inhibition of the effects of isoproterenol in the presence of iberiotoxin, whereas glibenclamide did not. We conclude that isoproterenol modulates the actions of levcromakalim through beta(1)-adrenoceptors and protein kinase A, even though K(ATP) channels do not contribute to its relaxant effects. However, the major relaxant mechanism for isoproterenol appears to be protein kinase A-independent activation of BK(Ca), with cyclic AMP-dependent mechanisms only being unmasked when the BK(Ca) mechanism is inhibited. Although direct G protein-mediated activation of BK(Ca) has been demonstrated previously in electrophysiological studies of single smooth muscle cells, this is the first time that such a mechanism has been shown to be functionally important in an intact blood vessel preparation.

ATP-Binding Cassette Transporters↗
PubMed2001

Drug resistance trends in M. tuberculosis: Blackburn 1990-1999.

SETTING: Blackburn, United Kingdom. OBJECTIVE: To describe the drug resistance data for Mycobacterium tuberculosis in white and Indian Subcontinent (ISC) ethnic patients in a high prevalence district in the United Kingdom (UK) over a 10-year period. DESIGN: Data from a detailed prospective clinical and epidemiological database of all notified patients were examined for the years 1990-1999 inclusive. RESULTS: Primary isoniazid resistance was found in 17/229 (7.4%) of ISC and 3/67 (4.5%) of white isolates. There was no statistical difference in the rates of drug resistance in those of ISC ethnic origin, whether they were ISC or UK born and whether or not they had made return visits to the ISC. CONCLUSION: The rate of primary isoniazid resistance remains between 5-10% in ISC patients in Blackburn, showing no fall from previous surveys. The rate of drug resistance was not lower in those born in the UK, irrespective of whether return visits had been made to the ISC. These data will need to be further monitored.

Antitubercular Agents↗
PubMed2001

Prince Edward Island Heart Health Dissemination Research Project: establishing a sustainable community mobilization initiative.

This paper provides an overview of the Prince Edward Island Heart Health Program (PEIHHP) Dissemination Research Project. Prince Edward Island (PEI) is a small province in the Atlantic region of Canada with a population of 137,980. The Island's economy is dependent on the fishery, agriculture, and tourism industries. Although unemployment rates are high (14.4%), Prince Edward Island has the lowest poverty rate in the country at 15.2%, high levels of social support (86%), and the second lowest rate of high chronic stress (Report on the Health of Canadians, 1996, 1999).

Cardiovascular Diseases↗
PubMed2000

Differential effects of xenoestrogens on coactivator recruitment by estrogen receptor (ER) alpha and ERbeta.

It has been proposed that tissue-specific estrogenic and/or antiestrogenic actions of certain xenoestrogens may be associated with alterations in the tertiary structure of estrogen receptor (ER) alpha and/or ERbeta following ligand binding; changes which are sensed by cellular factors (coactivators) required for normal gene expression. However, it is still unclear whether xenoestrogens affect the normal behavior of ERalpha and/or ERbeta subsequent to receptor binding. In view of the wide range of structural forms now recognized to mimic the actions of the natural estrogens, we have assessed the ability of ERalpha and ERbeta to recruit TIF2 and SRC-1a in the presence of 17beta-estradiol, genistein, diethylstilbestrol, 4-tert-octylphenol, 2',3',4', 5'-tetrachlorobiphenyl-ol, and bisphenol A. We show that ligand-dependent differences exist in the ability of ERalpha and ERbeta to bind coactivator proteins in vitro, despite the similarity in binding affinity of the various ligands for both ER subtypes. The enhanced ability of ERbeta (over ERalpha) to recruit coactivators in the presence of xenoestrogens was consistent with a greater ability of ERbeta to potentiate reporter gene activity in transiently transfected HeLa cells expressing SRC-1e and TIF2. We conclude that ligand-dependent differences in the ability of ERalpha and ERbeta to recruit coactivator proteins may contribute to the complex tissue-dependent agonistic/antagonistic responses observed with certain xenoestrogens.

Air Pollutants, Occupational↗
PubMed2000

Links between premarital sexual behaviour and extramarital intercourse: a multi-site analysis.

OBJECTIVES: Data from Côte d'Ivoire, Tanzania, Lusaka and Thailand were used to explore the relationship between premarital and extramarital sexual activity in men. DESIGN: Analysis was performed on data collected in the Global Programme on AIDS/WHO programme of stratified probability sample surveys of sexual behaviour of men and women aged 15 to at least 49 years interviewed face to face in 1989/1990. This analysis was restricted to male respondents currently married or in a regular partnership for at least a year. METHODS: Predictors of extramarital intercourse (EMI) in the preceding year were assessed using crude and adjusted odds ratios (OR), and 95% confidence intervals were calculated for a set of behavioural and sociodemographic variables that were believed a priori to be associated with EMI. RESULTS: Bivariate analysis showed that younger age at sexual debut, marriage to someone other than the debut partner and a higher number of sex partners before first marriage were significantly associated with enhanced probability of EMI in the past year in all sites. The adjusted OR indicated that in Côte d'lvoire and Tanzania the age at debut and in Tanzania and Thailand the number of sex partners before marriage were significantly associated with EMI in the past year. CONCLUSION: Characteristics of premarital conduct such as age at sexual debut, length of acquaintance with debut partner and number of premarital partners were significantly associated with EMI in men later in life. This continuity in sexual conduct over the life course was open to several competing interpretations, but sexual socialization in adolescence was likely to be at least a contributory factor.

Adolescent↗
PubMed2000

First human experience with pulmonary vein isolation using a through-the-balloon circumferential ultrasound ablation system for recurrent atrial fibrillation.

BACKGROUND: Standard mapping and ablation of focal sources of atrial fibrillation are associated with very long procedure times and low efficacy. An anatomic approach to complete pulmonary vein isolation could overcome these limitations. METHODS AND RESULTS: Fifteen patients with atrial fibrillation refractory to medication underwent circumferential isolation of the pulmonary veins by using a novel catheter, with an ultrasound transducer (8-MHz) mounted near the tip, in a saline-filled balloon. Twelve atrial foci and/or atrial fibrillation triggers were identified in 9 patients (pulmonary vein locations: left upper, 3; right upper, 6; right middle, 1; right lower, 1; and left inferior, 1). In 5 patients, lesions were placed in the absence of any mapped triggers. Irrespective of trigger mapping, circumferential isolation of both upper pulmonary veins was attempted in all patients. The lower pulmonary veins were ablated when sinus rhythm activation mapping revealed evidence of a sleeve of atrial muscle in the vein. The median number of lesions per patient required to isolate 1 pulmonary vein was 4 (range, 1 to 29). After ablation, no evidence of narrowing was seen with repeat venography or follow-up computed tomography scan. After a mean follow-up of 35+/-6 weeks, 5 patients had recurrence of atrial fibrillation. Three responded to drugs that were previously ineffective, and 2 remained in atrial fibrillation. CONCLUSIONS: This novel ultrasound ablation system can successfully isolate multiple pulmonary veins. At early follow-up, this approach seems to be effective in preventing recurrent atrial fibrillation in a significant number of patients.

Adult↗
PubMed2000

Montelukast, a leukotriene receptor antagonist, in combination with loratadine, a histamine receptor antagonist, in the treatment of chronic asthma.

BACKGROUND: Montelukast sodium, a potent, oral, specific leukotriene-receptor antagonist, has demonstrated clinical efficacy in the treatment of chronic asthma. Loratadine, a selective histamine type 1 (H(1))-receptor antagonist, has demonstrated antiallergic properties. Leukotriene-receptor antagonists given concomitantly with H(1)-receptor antagonists have been shown to have additive effects in the prevention of bronchospasm in antigen-challenge models. OBJECTIVE: To determine whether montelukast plus loratadine provides improved efficacy to montelukast alone in the treatment of chronic asthma. METHODS: The efficacy of montelukast alone vs montelukast-loratadine was studied in a 10-week, multicenter, randomized, double-blind, 2 x 2 crossover study. After a 2-week placebo run-in period, patients received montelukast sodium (10 mg) plus loratadine (20 mg), or montelukast sodium (10 mg) plus placebo once daily for 2 weeks. After a 2-week placebo washout period, patients were crossed over to receive 2 weeks of the other active treatment regimen, followed by another 2-week placebo washout period. RESULTS: Montelukast given concomitantly with loratadine caused significant improvement in percentage of change from baseline in forced expiratory volume in 1 second (FEV(1)) compared with montelukast alone (13.86% vs 9.72%; P =.001). The average additional effect of loratadine (least square mean difference in percentage of change from baseline in FEV(1)) was 4.15% (95% confidence interval, 1.65%-6.65%). Key secondary end points (mean daily beta-agonist use, daytime and nighttime symptom scores, morning and evening peak expiratory flow rate, and the Patient Global Evaluation) all showed significant improvement with montelukast-loratadine (P<.05). CONCLUSION: Montelukast-loratadine significantly improved end points of asthma control during a 2-week treatment period.

Acetates↗