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1 Department of Bioengineering
and Institute for Biomedical Engineering,
The mechanisms contributing to organ injury in
hypertension have been incompletely defined. The thymus gland of the
spontaneously hypertensive rat (SHR) shows significant atrophy at the
age of 15 wk compared with its normotensive control, the Wistar-Kyoto rat (WKY). The aim of the present study was to examine the thymus of
SHR for evidence of DNA nicking as one of the mechanisms for thymic
atrophy. SHR and WKY were subjected to adrenalectomy or sham surgery at
12 wk and studied at 15 wk. Adrenalectomy served to normalize the blood
pressure in the SHR. DNA nicking was detected by in situ nick-end
labeling (ISEL) of fixed tissue sections. Tissue sections were treated
with proteolysis, and terminal deoxyribonucleotidyl transferase was
used to incorporate biotinylated deoxynucleotides into DNA nick end in
situ. Separately, DNA fragmentation was evaluated by measuring the
level of released mono- and oligonucleosomes to the cytoplasm. A higher
number of thymic ISEL-positive cells and a higher level of cytoplasmic
mono- and oligonucleosomes were observed in SHR than in WKY. After
adrenalectomy the enhanced level of ISEL and cytoplasmic mono- and
oligonucleosomes in SHR was reduced to the level in WKY. Dexamethasone
treatment (0.05 mg · kg
1 · day
1)
in WKY serves to decrease the thymus weight and significantly elevate
the level of mono- and oligonucleosomes. Thus increased DNA
fragmentation represents one of the mechanisms associated with thymic
atrophy, a feature that reflects immune suppression in SHR.
in situ deoxyribonucleic acid nick-end labeling; adrenalectomy; glucocorticoid; apoptosis
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