There is evidence that withdrawal of SRIH infusion in man promotes a
rebound GH response that allegedly has been proposed to be related to
the function of GHRH-producing neurons. In the present study ...we have
evaluated whether a reduction in endogenous GHRH activity contributes
to the decreased GH secretion of the elderly. Sixteen young (8 women,
aged 23–32 yr, and 8 men, aged 18–27 yr) and 13 elderly (8 women,
aged 65–82 yr, and 5 men, aged 65–70 yr) healthy subjects volunteered
to participate in this investigation. Each subject was tested on 2
separate occasions: 1) a 90-min iv infusion of SRIH was given in 50 mL
0.9% saline delivered at a rate of 9 μg/kg·h; and 2) a 90-min iv
infusion of isovolumetric amounts of 0.9% saline was given. Plasma GH
levels were determined before and up to 180 min after SRIH or saline
infusion, whereas plasma insulin-like growth factor I, estradiol, and
testosterone levels were measured in basal samples. In elderly women,
the mean maximum (Δ) GH peak (2 ± 0.7 μg/L) after withdrawal
of SRIH infusion was significantly (P < 0.02)
lower than that in young women (7.3 ± 2 μg/L). In elderly men,
the mean Δ GH peak (2.9 ± 0.6 μg/L) after withdrawal of SRIH
infusion was lower than that in young men (6.3 ± 1.6 μg/L),
although the difference failed to achieve statistical significance.
Baseline insulin-like growth factor I levels were significantly lower
in elderly compared to young subjects in both men and in women. In
women, both age and basal plasma estradiol and testosterone levels
significantly correlated with Δ GH peak after SRIH withdrawal (r=
−0.61, r = 0.61, and r = 0.66, respectively), whereas in
men they did not. These findings are compatible with the view that an
age-related decrease in endogenous GHRH function may contribute to the
defective GH secretion of the elderly. Alterations in plasma
concentrations of sex steroids may have important implications in the
observed changes.
In vivo activation of platelets can be accurately measured by radioimmunoassays of platelet factor 4 (PF4) and beta thromboglobulin (beta TG). Studies that attempt to correlate increases in PF4 and ...beta TG levels with exercise-induced myocardial ischemia have yielded conflicting results. To further examine the natural history of release of PF4 and beta TG we used a method of serial samplings of these proteins during and after exercise in nine normal subjects and 24 patients with coronary artery disease (CAD). Mean values for PF4 and beta TG at rest, during each stage, and immediately after treadmill exercise were the same for normal subjects and for patients with positive and negative responses to exercise-tolerance tests (ETTs). However, nonparametric analysis and regression equations disclosed differences in trends of PF4 level during exercise; PF4 levels increased in normal subjects during exercise, while patients with positive ETTs had no change in PF4 levels and patients with negative ETTs actually showed a decrease in PF4. This investigation confirmed that exercise-induced myocardial ischemia is not associated with platelet aggregation as manifested by the release of the platelet-specific proteins PF4 and beta TG. Statistical analysis suggested that prior reports of elevated levels of PF4 during exercise could have been caused by technical and methodologic difficulties that were associated with the collection and handling of the samples.
Purpose: To measure chromosome aberrations in C3H 10T1/2 mouse fibroblasts using FISH painting at the first mitosis following exposure to 30 keV/ mu m hydrogen or neon ions. Materials and methods: ...Cells in plateau-phase were irradiated with 0.86 MeV protons at the TTT-3 Tandem accelerator in Naples (Italy), or with 400 MeV/n Ne ions at the HIMAC accelerator in Chiba (Japan). Colcemid-blocked cells were harvested at the first mitosis following exposure, and chromosome spreads were hybridized in situ with a fluorescein-labelled composite mouse DNA probe specific for chromosomes 2 and 8. Results: Protons were more efficient than neon ions at the same LET in the induction of chromosome interchanges and breaks. Yields of complex exchanges were similar for both particles at the same dose, but protons produced mostly insertions, while with Ne exposure non-reciprocal exchanges were the most frequent complex-type exchange. Conclusions: Charged particles with the same LET produce different yields of chromosome aberrations, and some observed differences can be explained based on the available track-structure models.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Nucl.Phys. B500 (1997) 513-543 By using the results of a high-statistics (O(10^7) measurements) Monte Carlo
simulation we test several predictions of perturbation theory on the O(n)
non-linear ...sigma-model in 2 dimensions. We study the O(3) and O(8) models on
large enough lattices to have a good control on finite-size effects. The
magnetic susceptibility and three different definitions of the correlation
length are measured. We check our results with large-n expansions as well as
with standard formulae for asymptotic freedom up to 4 loops in the standard and
effective schemes.
For this purpose the weak coupling expansions of the energy up to 4 loops for
the standard action and up to 3 loops for the Symanzik action are calculated.
For the O(3) model we have used two different effective schemes and checked
that they lead to compatible results. A great improvement in the results is
obtained by using the effective scheme based on the energy at 3 and 4 loops. We
find that the O(8) model follows very nicely (within few per mille) the
perturbative predictions. For the O(3) model an acceptable agreement (within
few per cent) is found.
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