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Biomedical subjects

B Williams

Publications and source records attributed to B Williams.

At least 127 records · Page 7Linked to original sources
PubMed2000

Clinical implication of antiembolic trials in atrial fibrillation and role of transesophageal echocardiography in atrial fibrillation.

Risk for stroke in patients with atrial fibrillation (AF) is highly heterogeneous. Increasing age, history of diabetes, hypertension, previous transient ischemic attack or stroke, and poor ventricular function are independent risk factors for stroke in patients with AF. Accordingly, some groups of patients with AF have low risk and some have high risk. In general, patients at high risk benefit most from anticoagulation therapy with warfarin. In general, if a patient is younger than 65 years of age and has none of the defined risk factors, the stroke rate without prophylaxis (aspirin or warfarin) is low. In patients 65 to 75 years of age with no risk factors, the risk for stroke is low with either aspirin or warfarin therapy; the choice is left to the caretaking physician. All patients older than 75 years and all patients of any age who have risk factors obtain striking benefit from the use of anticoagulation with warfarin. This benefit far outweighs any risk for major hemorrhage.

Age Factors↗
PubMed2000

Localization of the sites mediating desensitization of the beta(2)-adrenergic receptor by the GRK pathway.

The human beta(2)-adrenergic receptor (betaAR) is rapidly desensitized in response to saturating concentrations of agonist by G protein-coupled receptor kinases (GRKs) and cAMP-dependent protein kinase A (PKA) phosphorylation of the betaAR, followed by beta-arrestin binding and receptor internalization. betaAR sites phosphorylated by GRK in vivo have not yet been identified. In this study, we examined the role of the carboxyl terminal serines, 355, 356, and 364, in the GRK-mediated desensitization of the betaAR. Substitution mutants of these serine residues were constructed in which either all three (S355,356,364A), two (S355,356A and S356, 364A), or one of the serines (S356A and S364A) were modified. These mutants were constructed in a betaAR in which the serines of the PKA consensus site were substituted with alanines (designated PKA(-)) to eliminate any PKA contribution to desensitization, and they were stably transfected into human embryonic kidney 293 cells. Treatment of the PKA(-) mutant with 10 microM epinephrine for 5 min caused a 3. 5-fold increase in the EC(50) value and a 42% decrease in the V(max) value for epinephrine stimulation of adenylyl cyclase. Substitution of all three serines completely inhibited the epinephrine-induced shift in the EC(50). Both double mutants, S355,356A and S356,364A, showed a nearly complete loss of the EC(50) shift, whereas the single substitutions, S356A and S364A, caused only a slight decrease in desensitization. None of the mutations altered the epinephrine-induced decrease in V(max,) which seems to be downstream of the receptor. The triple mutation caused a 45% decrease in epinephrine-induced internalization and a 90 to 95% reduction in phosphorylation of the betaAR relative to the PKA(-) (1.9+/- 0.2- and 16.6+/-3.8-fold phosphorylation over basal, respectively). The double mutants caused an intermediate reduction in internalization (20-21%) and phosphorylation (43-52%). None of the serine mutations altered the rate of betaAR recycling. Our data demonstrate that the cluster of serines within the 355 to 364 betaAR domain confer the rapid, GRK-mediated, receptor-level desensitization of the betaAR.

Adenylyl Cyclases↗
PubMed2000

Influence of hypertension, left ventricular hypertrophy, and left ventricular systolic dysfunction on plasma N terminal proBNP.

OBJECTIVES: To examine the relation between plasma concentration of the N terminal of the precursor of brain natriuretic peptide (NT proBNP), left ventricular hypertrophy (LVH), and left ventricular systolic dysfunction (LVSD) in patients with a history of hypertension. DESIGN: Prospective study. SETTING: Teaching hospital based study. PATIENTS: NT proBNP concentrations were determined in five groups of individuals. Group 1: 15 echocardiographic normal controls; group 2: 22 patients with hypertension, normal left ventricular systolic function, and no LVH; group 3: 24 patients with hypertension, normal left ventricular systolic function, and LVH; group 4: 13 patients with history of hypertension, no history of ischaemic heart disease, and left ventricular wall motion index (WMI) between 1.9-1.3; and group 5:17 patients with a history of hypertension, no history of ischaemic heart disease, and WMI < 1.2. RESULTS: Median (range) NT proBNP concentrations (in fmol/ml) for groups 1-5, respectively, were: 129.4 (53.6-159.7), 147.4 (54.3-730. 5), 137.1 (35.8-403.9), 356.7 (124.4-934.4), and 493.5 (248.9-909). Mean log NT proBNP differed among all five groups (p < 0.0001), and between groups 4 and 5 versus groups 1-3 (p < 0.0001), and group 4 versus group 5 (p = 0.02) only. CONCLUSIONS: The results suggest that the presence of hypertension with or without LVH (and normal left ventricular systolic function) does not affect NT proBNP concentrations. Moreover, there is a significant rise in NT proBNP only when LVSD develops in hypertension. Thus, NT proBNP remains a useful diagnostic aid for LVSD, even in hypertensive patients.

Adult↗
PubMed2000

VEGF and ATP act by different mechanisms to increase microvascular permeability and endothelial [Ca(2+)](i).

Vascular endothelial growth factor (VEGF) increases hydraulic conductivity (L(p)) by stimulating Ca(2+) influx into endothelial cells. To determine whether VEGF-mediated Ca(2+) influx is stimulated by release of Ca(2+) from intracellular stores, we measured the effect of Ca(2+) store depletion on VEGF-mediated increased L(p) and endothelial intracellular Ca(2+) concentration ([Ca(2+)](i)) of frog mesenteric microvessels. Inhibition of Ca(2+) influx by perfusion with NiCl(2) significantly attenuated VEGF-mediated increased [Ca(2+)](i). Depletion of Ca(2+) stores by perfusion of vessels with thapsigargin did not affect the VEGF-mediated increased [Ca(2+)](i) or the increase in L(p). In contrast, ATP-mediated increases in both [Ca(2+)](i) and L(p) were inhibited by thapsigargin perfusion, demonstrating that ATP stimulated store-mediated Ca(2+) influx. VEGF also increased Mn(2+) influx after perfusion with thapsigargin, whereas ATP did not. These data showed that VEGF increased [Ca(2+)](i) and L(p) even when Ca(2+) stores were depleted and under conditions that prevented ATP-mediated increases in [Ca(2+)](i) and L(p). This suggests that VEGF acts through a Ca(2+) store-independent mechanism, whereas ATP acts through Ca(2+) store-mediated Ca(2+) influx.

Adenosine Triphosphate↗
PubMed2000

Mechanical strain-induced extracellular matrix production by human vascular smooth muscle cells: role of TGF-beta(1).

Elevated blood pressure imposes increased mechanical stress on the vascular wall, and mechanical strain is a mitogenic stimulus for vascular smooth muscle (VSM) cells. The role of mechanical forces in regulating the production of noncellular material by VSM cells for VSM cells of human origin remains undefined. We thus investigated the effects of chronic cyclical mechanical strain on extracellular matrix (ECM) protein production by cultured human VSM cells. To simulate a blood pressure of 120/80 mm Hg, human VSM cells were repetitively stretched and relaxed by 10% to 16% of their original length with the Flexercell apparatus. Fibronectin and collagen protein concentrations, matrix metalloproteinase (MMP) activity, and transforming growth factor-beta(1) (TGF-beta(1)) mRNA expression by human VSM cells were measured in response to mechanical strain. Exposing human VSM cells to 5 days of chronic cyclical mechanical strain increased fibronectin (+48%, P:<0.01) and collagen (+50%, P:<0.001) concentrations when compared with cells grown in static conditions. Mechanical strain also increased MMP-2 activity, the predominant matrix-degrading isoform (+11%, P:<0.05) in human VSM cells, thus strain-induced ECM accumulation was not due to inhibition of ECM protein degradation. Strain also increased TGF-beta(1) mRNA expression and the production of a soluble factor that increased ECM protein production. Moreover, a TGF-beta-blocking antibody inhibited the effect of strain-conditioned media on matrix production by human VSM cells. These results suggest that chronic cyclical mechanical strain can directly modulate the fibrogenic activity of human VSM cells by inducing ECM protein synthesis and MMP activity. This occurs, at least in part, through mechanical strain-induced TGF-beta(1) production, a mechanism that could explain the increased vascular ECM deposition in hypertension.

Analysis of Variance↗
PubMed2000

Oestradiol is a potent mitogen and modulator of GnRH signalling in alphaT3-1 cells: are these effects causally related?

GnRH acts via phospholipase C (PLC) activating G-protein coupled receptors to stimulate secretion of gonadotrophins from gonadotrophs. These cells are also regulated by gonadal steroids, which act centrally to influence GnRH secretion, and peripherally to modulate GnRH action. We have shown that oestradiol can stimulate proliferation and modulate GnRH-stimulated [(3)H]inositol phosphate ([(3)H]IP(x)) accumulation (used as a measure of PLC activity) in a gonadotroph-derived cell line (alphaT3-1). Here we show that when alphaT3-1 cells were incubated in medium with 2% foetal calf serum (FCS), [(3)H]thymidine incorporation was not stimulated by oestradiol but was reduced to <2% of control by the oestrogen antagonist, raloxifene. The inhibitory effect of 10 or 1000 nM raloxifene was reversed competitively by oestradiol. A similar pattern of effects was seen when effects of oestradiol and raloxifene on the proportion of cells in the S-phase of the cell cycle (as measured by flow cytometry of propidium iodide-labelled cells) and on oestrogen receptor activity (as measured by trans-activation of the oestrogen-response elements in the vitellogenin promoter) were quantified. In addition, RT-PCR revealed expression of alpha and beta (but not beta2) subtypes of oestrogen receptors. Thus, oestrogen is an essential mitogen for alphaT3-1 cells, its mitogenic effect is oestrogen receptor mediated and is associated with a marked alteration of cell cycle distribution, and the full extent of these effects are best revealed in the presence of raloxifene. Using this strategy, we found that cells cultured for 4 days with 10 nM raloxifene expressed GnRH receptors (K(d) for (125)I-buserelin 4.33 nM) and that their activation by GnRH caused a concentration-dependent increase in [(3)H]IP(x) (in cells labelled with [(3)H]inositol) and inositol 1,4,5 trisphophate (in unlabelled cells). Addition of 10 nM oestradiol (to overcome receptor blockade by raloxifene) reduced GnRH receptor number by 31% but increased maximal effects on [(3)H]IP(x) and Ins(1,4,5)P(3) approximately 4-fold. The effects of oestradiol on GnRH receptor number and signalling were not, however, mimicked by culture for 2 days in medium with 10% FCS and the S-phase blocker, thymidine (15 mM). This treatment increased the proportion of cells in the S-phase 2- to 3-fold but did not alter GnRH receptor number or signalling. Other treatments which altered cell cycle transition (hydroxyurea, colcemid, methotrexate) also failed to alter GnRH receptor number or signalling and no correlation was seen between GnRH receptor number or GnRH-stimulated [(3)H]IP(x) accumulation and the proportion of cells in the S-phase or G2/M-phases of the cell cycle. Thus, oestradiol has pronounced effects on GnRH signalling, proliferation and cell cycle distribution in alphaT3-1 cells, but these trophic effects do not underlie the modulation of GnRH signalling.

Animals↗
PubMed2000

Mechanical strain-induced human vascular matrix synthesis: the role of angiotensin II.

INTRODUCTION: Reduced vascular compliance in patients with hypertension results from an increase in extra-cellular matrix (ECM) protein deposition in blood vessels. At least two key factors, namely mechanical strain and neurohumoral mediators, for example Angiotensin II (Ang II), promote fibrogenesis within vessel walls; however potential interactions between these have not been clearly defined. This work examined the direct effect of mechanical strain on matrix mRNA expression and protein synthesis by human vascular smooth muscle (VSM) cells and identified the importance of renin-angiotensin system (RAS) activation in stretch-induced matrix production. METHODS: Human VSM cells were exposed either to a cyclical mechanical strain regimen or to Ang II in the presence or absence of the Ang II receptor (AT(1) R) antagonist losartan or its more potent metabolite EXP3174. Analysis of matrix mRNA expression (Northerns) and protein synthesis (ELISA) and cellular AT(1)-receptor protein expression (Westerns) were determined. RESULTS: Ang II increased both collagen alpha1 (92%, SEM +/- 20%) mRNA expression and fibronectin (21% +/- 6%) protein synthesis in static VSM cells compared with unstimulated controls. The effect of Ang II was attenuated by antagonism of the AT(1)-receptor (AT(1) R). Similarly, mechanical strain induced an increase in both collagen alpha1 (102% +/- 30%) mRNA expression and fibronectin (50% +/-21%) protein synthesis. Surprisingly, in the absence of exogenous Ang II, AT(1)-receptor blockade attenuated this stretch-induced increase in matrix synthesis. Mechanical strain also induced an increase in total cellular AT(1)-receptor protein (30.7% +/- 3.5%) compared with static cells. CONCLUSION: Both mechanical strain and Ang II increased matrix gene expression and protein synthesis by human VSM cells. The effect of strain was attenuated by AT(1)-receptor antagonism. Our results further suggest that mechanical strain may sensitise human VSM cells to the fibrogenic actions of Ang II, perhaps via upregulation of the AT(1)-receptor.

Angiotensin II↗
PubMed2000

Tobacco settlement dollars a "burning issue" for TMA.

More than 46 states and five U. S. territories have their collective hands outstretched as the tobacco industry digs into its deep pockets to make amends for the ill effects of its product. Even as Tennessee lawmakers debate the best use of an anticipated $215 million windfall, fears are growing that very few of the tobacco settlement dollars will go toward their intended purpose.

Adult↗
PubMed2000

Evaluating the impact of tuberculosis control: number of deaths prevented by short-course chemotherapy in China.

BACKGROUND: Tuberculosis (TB) is still amongst the most important causes of human morbidity and mortality, killing approximately two million people each year. Standard short-course chemotherapy (SSCC) can rapidly control illness and dramatically reduce the chance of death, but the impact of treatment has rarely been evaluated in these terms. METHOD: We developed a mathematical model that makes use of routinely-collected data to calculate the number of deaths directly prevented by TB treatment (i.e. excluding those due to reduced transmission). The method was applied to the world's largest TB control programme covering over 500 million people in 12 provinces of China. RESULTS: Counties which had been enrolled in the programme since 1991 were, by 1997, preventing at least 46% (37-56%) of the TB deaths that would otherwise have occurred. If replicated across the entire TB control programme area, this would amount to 30 000 (range 26 000-59 000) deaths directly prevented each year. CONCLUSIONS: Short-course chemotherapy has substantially reduced TB mortality in half of China. The analytical method described here could be applied to TB control operations in many other countries, and should help to quantify the true burden of tuberculosis alleviated by SSCC.

Anti-Bacterial Agents↗
PubMed2000

Measuring the "managedness" and covered benefits of health plans.

STUDY AIMS: (1) To develop indexes measuring the degree of managedness and the covered benefits of health insurance plans, (2) to describe the variation in these indexes among plans in one health insurance market, (3) to assess the validity of the health plan indexes, and (4) to examine the association between patient characteristics and the health plan indexes. Measures of the "managedness" and covered benefits of health plans are requisite for studying the effects of managed care on clinical practice and health system performance, and they may improve people's understanding of our complex health care system. DATA SOURCES/STUDY SETTING: As part of our larger Physician Referral Study, we collected health insurance information for 189 insurance product lines and 755 products in the Seattle, Washington metropolitan area, which we linked with the study's data for 2,277 patients recruited in local primary care offices. STUDY DESIGN: Managed care and benefit variables were constructed through content analysis of health plan information. Principal component analysis of the variables produced a managedness index, an in-network benefits index, and an out-of-network benefits index. Bivariable analyses examined associations between patient characteristics and the three indexes. PRINCIPAL FINDINGS: From the managed care variables, we constructed three provider-oriented indexes for the financial, utilization management, and network domains of health plans. From these, we constructed a single managedness index, which correlated as expected with the individual measures, with the domain indexes, with plan type (FFS, PPO, POS, HMO), with independent assessments of local experts, and with patients' attitudes about their health insurance. For benefits, we constructed an in-network benefits index and an out-of-network benefits index, which were correlated with the managedness index. The personal characteristics of study patients were associated with the managed care and benefit indexes. Study patients in more managed plans reported somewhat better health than patients in less managed plans. CONCLUSIONS: Indexes of the managedness and benefits of health plans can be constructed from publicly available information. The managedness and benefit indexes are associated with the personal characteristics and health status of study patients. Potential uses of the managed care and benefits indexes are discussed.

Abstracting and Indexing↗