50 research outputs found
Altered renal hemodynamics and impaired myogenic responses in the fawn-hooded rat
The present study examined whether an abnormality in the myogenic response
of renal arterioles that impairs autoregulation of renal blood flow (RBF)
and glomerular capillary pressure (PGC) contributes to the development of
renal damage in fawn-hooded hypertensive (FHH) rats. Autoregulation of
whole kidney, cortical, and medullary blood flow and PGC were compared in
young (12 wk old) FHH and fawn-hooded low blood pressure (FHL) rats in
volume-replete and volume-expanded conditions. Baseline RBF, cortical and
medullary blood flow, and PGC were significantly greater in FHH than in
FHL rats. Autoregulation of renal and cortical blood flow was
significantly impaired in FHH rats compared with results obtained in FHL
rats. Myogenically mediated autoregulation of PGC was significantly
greater in FHL than in FHH rats. PGC rose from 46 +/- 1 to 71 +/- 2 mmHg
in response to an increase in renal perfusion pressure from 100 to 150
mmHg in FHH rats, whereas it only increased from 39 +/- 2 to 53 +/- 1 mmHg
in FHL rats. Isolated perfused renal interlobular arteries from FHL rats
constricted by 10% in response to elevations in transmural pressure from
70 to 120 mmHg. In contrast, the diameter of vessels from FHH rats
increased by 15%. These results indicate that the myogenic response of
small renal arteries is altered in FHH rats, and this contributes to an
impaired autoregulation of renal blood flow and elevations in PGC in this
strain
Impaired autoregulation of renal blood flow in the fawn-hooded rat
The responses to changes in renal perfusion pressure (RPP) were compared
in 12-wk-old fawn-hooded hypertensive (FHH), fawn-hooded low blood
pressure (FHL), and August Copenhagen Irish (ACI) rats to determine
whether autoregulation of renal blood flow (RBF) is altered in the FHH
rat. Mean arterial pressure was significantly higher in conscious,
chronically instrumented FHH rats than in FHL rats (121 +/- 4 vs. 109 +/-
6 mmHg). Baseline arterial pressures measured in
ketamine-Inactin-anesthetized rats averaged 147 +/- 2 mmHg (n = 9) in FHH,
132 +/- 2 mmHg (n = 10) in FHL, and 123 +/- 4 mmHg (n = 9) in ACI rats.
Baseline RBF was significantly higher in FHH than in FHL and ACI rats and
averaged 9.6 +/- 0.7, 7.4 +/- 0.5, and 7.8 +/- 0.9 ml. min-1. g kidney
wt-1, respectively. RBF was autoregulated in ACI and FHL but not in FHH
rats. Autoregulatory indexes in the range of RPPs from 100 to 150 mmHg
averaged 0.96 +/- 0.12 in FHH vs. 0.42 +/- 0.04 in FHL and 0.30 +/- 0.02
in ACI rats. Glomerular filtration rate was 20-30% higher in FHH than in
FHL and ACI rats. Elevations in RPP from 100 to 150 mmHg increased urinary
protein excretion in FHH rats from 27 +/- 2 to 87 +/- 3 microg/min,
whereas it was not significantly altered in FHL or ACI rats. The
percentage of glomeruli exhibiting histological evidence of injury was not
significantly different in the three strains of rats. These results
indicate that autoregulation of RBF is impaired in FHH rats before the
development of glomerulosclerosis and suggest that an abnormality in the
control of renal vascular resistance may contribute to the development of
proteinuria and renal failure in this strain of rats
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
First Measurement of Z/gamma* Production in Compton Scattering of Quasi-real Photons
We report the first observation of Z/gamma* production in Compton scattering
of quasi-real photons. This is a subprocess of the reaction e+e- to
e+e-Z/gamma*, where one of the final state electrons is undetected.
Approximately 55 pb-1 of data collected in the year 1997 at an e+e-
centre-of-mass energy of 183 GeV with the OPAL detector at LEP have been
analysed. The Z/gamma* from Compton scattering has been detected in the
hadronic decay channel. Within well defined kinematic bounds, we measure the
product of cross-section and Z/gamma* branching ratio to hadrons to be
(0.9+-0.3+-0.1) pb for events with a hadronic mass larger than 60 GeV,
dominated by (e)eZ production. In the hadronic mass region between 5 GeV and 60
GeV, dominated by (e)egamma* production, this product is found to be
(4.1+-1.6+-0.6) pb. Our results agree with the predictions of two Monte Carlo
event generators, grc4f and PYTHIA.Comment: 18 pages, LaTeX, 5 eps figures included, submitted to Physics Letters
Measurement of the B0 Lifetime and Oscillation Frequency using B0->D*+l-v decays
The lifetime and oscillation frequency of the B0 meson has been measured
using B0->D*+l-v decays recorded on the Z0 peak with the OPAL detector at LEP.
The D*+ -> D0pi+ decays were reconstructed using an inclusive technique and the
production flavour of the B0 mesons was determined using a combination of tags
from the rest of the event. The results t_B0 = 1.541 +- 0.028 +- 0.023 ps, Dm_d
= 0.497 +- 0.024 +- 0.025 ps-1 were obtained, where in each case the first
error is statistical and the second systematic.Comment: 17 pages, 4 figures, submitted to Phys. Lett.
Search for Higgs Bosons in e+e- Collisions at 183 GeV
The data collected by the OPAL experiment at sqrts=183 GeV were used to
search for Higgs bosons which are predicted by the Standard Model and various
extensions, such as general models with two Higgs field doublets and the
Minimal Supersymmetric Standard Model (MSSM). The data correspond to an
integrated luminosity of approximately 54pb-1. None of the searches for neutral
and charged Higgs bosons have revealed an excess of events beyond the expected
background. This negative outcome, in combination with similar results from
searches at lower energies, leads to new limits for the Higgs boson masses and
other model parameters. In particular, the 95% confidence level lower limit for
the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons
can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA >
72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and
soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for
minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM
parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European
Physical Journal
A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays
The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where
Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL
detector at LEP. Lambda_b are selected by the presence of energetic Lambda
particles in bottom events tagged by the presence of displaced secondary
vertices. A fit to the momenta of the Lambda particles separates signal from B
meson and fragmentation backgrounds. The measured product branching ratio is
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))%
Combined with a previous OPAL measurement, one obtains
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.Comment: 16 pages, LaTeX, 3 eps figs included, submitted to the European
Physical Journal
WW Production Cross Section and W Branching Fractions in e+e- Collisions at 189 GeV
From a data sample of 183 pb^-1 recorded at a center-of-mass energy of roots
= 189 GeV with the OPAL detector at LEP, 3068 W-pair candidate events are
selected. Assuming Standard Model W boson decay branching fractions, the W-pair
production cross section is measured to be sigmaWW = 16.30 +- 0.34(stat.) +-
0.18(syst.) pb. When combined with previous OPAL measurements, the W boson
branching fraction to hadrons is determined to be 68.32 +- 0.61(stat.) +-
0.28(syst.) % assuming lepton universality. These results are consistent with
Standard Model expectations.Comment: 22 pages, 5 figures, submitted to Phys. Lett.
Measurement of the Michel Parameters in Leptonic Tau Decays
The Michel parameters of the leptonic tau decays are measured using the OPAL
detector at LEP. The Michel parameters are extracted from the energy spectra of
the charged decay leptons and from their energy-energy correlations. A new
method involving a global likelihood fit of Monte Carlo generated events with
complete detector simulation and background treatment has been applied to the
data recorded at center-of-mass energies close to sqrt(s) = M(Z) corresponding
to an integrated luminosity of 155 pb-1 during the years 1990 to 1995. If e-mu
universality is assumed and inferring the tau polarization from neutral current
data, the measured Michel parameters are extracted. Limits on non-standard
coupling constants and on the masses of new gauge bosons are obtained. The
results are in agreement with the V-A prediction of the Standard Model.Comment: 32 pages, LaTeX, 9 eps figures included, submitted to the European
Physical Journal