934 research outputs found
Interperson variability but intraperson stability of baseline plasma cortisol concentrations, and its relation to feedback sensitivity of the hypothalamo-pituitary-adrenal axis to a low dose of dexamethasone in elderly individuals
In the present study, we investigated whether the negative feedback action
of glucocorticoids (GCs) on the hypothalamo-pituitary-adrenal (HPA) axis
changes with age. We performed a 1-mg dexamethasone (DEX) suppression test
in 216 healthy elderly individuals. To investigate individual variability
of feedback sensitivity in more detail, 2.5 yr later a 0.25-mg DEX
suppression test was carried out in 164 of the same individuals. We
investigated whether there was an effect of age or gender on both basal
and post-DEX cortisol levels, as well as on the concentration of DEX.
Furthermore, we examined whether the reactions to the two doses of DEX
differed, and whether indications for an intraperson stability of baseline
cortisol levels could be found. Neither the pre- nor the post-1-mg DEX
plasma cortisol concentrations showed a correlation with age, and there
were no differences between men and women. The same was true for the pre-
and post-0.25-mg DEX cortisol concentrations. In reaction to 1 mg DEX,
over 90% of the subjects investigated showed a cortisol suppression to
levels below 50 nmol/L. After the administration of 0.25 mg DEX, there was
a much wider range in post-DEX cortisol concentrations. After the
administration of 1 mg DEX, there was a significant correlation between
liver function parameters and plasma DEX concentrations in males, and
there was a correlation between body mass index and plasma DEX
concentration in females. Plasma DEX concentrations after the
administration of 1 mg and 0.25 mg DEX were closely correlated within
subjects (P < 0.001). There was an intraindividual stability of serum
cortisol levels determined at an interval of 2.5 yr. Furthermore, the
individuals with the highest baseline cortisol concentrations also had the
highest post-0.25-mg DEX cortisol concentrations, indicating a close
relationship between basal cortisol levels and the feedback sensitivity of
the HPA axis to a low dose of DEX. These observations suggest a genetic
influence on the set point of the HPA axis. Aging does not seem to lead to
a change in HPA activity as measured by early morning total cortisol
levels. Also, no changes in the sensitivity of the feedback system to DEX
were observed with age. DEX metabolism is influenced by liver function (in
males) and by body mass index (in females)
A polymorphism in the glucocorticoid receptor gene may be associated with and increased sensitivity to glucocorticoids in vivo
We investigated whether a polymorphism at nucleotide position 1220,
resulting in an asparagine-to-serine change at codon 363 in the
glucocorticoid receptor (GR) gene is associated with an altered
sensitivity to glucocorticoids. In a group of 216 elderly persons, 13
heterozygotes for the N363S polymorphism were identified by PCR/single
strand conformation polymorphism analysis. In 2 dexamethasone (DEX)
suppression tests (DSTs), using 1 and 0.25 mg DEX, the circulating
cortisol and insulin concentrations were compared between N363S carriers
and controls. In the 1-mg DST, there were no differences between N363S
carriers and controls, with respect to adrenal suppression, but there was
a significantly higher (P < 0.05) insulin response in N363S carriers. In
the 0.25-mg DST, a significantly larger (P < 0.05) cortisol suppression
and higher (P < 0.05) insulin response were seen in N363S carriers.
Comparison of blood pressure, body mass index (BMI), and bone mineral
density (BMD) between the N363S carriers and controls showed that N363S
carriers had a higher (P < 0.05) BMI but normal blood pressure. There was
an obvious trend towards lower age-, BMI-, and sex-adjusted BMD in the
lumbar spine in N363S carriers. GR characteristics measured in 41 controls
and 9 N363S carriers in peripheral mononuclear leucocytes showed no
differences between N363S carriers and controls, with respect to GR number
and ligand binding affinity. However, there was a trend towards greater
sensitivity to DEX in the carriers' lymphocytes, in a mitogen-induced cell
proliferation assay. In transfection assays, the capacity of the codon 363
variant to activate mouse mammary tumor virus promotor-mediated
transcription in COS-1 cells was unaltered, when compared with the
wild-type GR. We conclude that in 6.0% of our study population, a
polymorphism in codon 363 of the GR gene was found. Individuals carrying
this polymorphism seemed healthy at clinical examination but had a higher
sensitivity to exogenously administered glucocorticoids, with respect to
both cortisol suppression and insulin response. Life-long exposure to the
mutated allele may be accompanied by an increased BMI and a lowered BMD in
the lumbar spine but does not affect blood pressure
An algebraic SU(1,1) solution for the relativistic hydrogen atom
The bound eigenfunctions and spectrum of a Dirac hydrogen atom are found
taking advantage of the Lie algebra in which the radial part of the
problem can be expressed. For defining the algebra we need to add to the
description an additional angular variable playing essentially the role of a
phase. The operators spanning the algebra are used for defining ladder
operators for the radial eigenfunctions of the relativistic hydrogen atom and
for evaluating its energy spectrum. The status of the Johnson-Lippman operator
in this algebra is also investigated.Comment: to appear in Physics Letters A (2005). We corrected a misprint in
page 7, in the paragraph baggining with "With the value of ..." the ground
state should be |\lambda, \lambda>, not |\lambda, \lambda+1
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
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