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1 Department of Health and Kinesiology, Texas A&M University, and 2 Department of Medical Physiology and the Cardiovascular Research Institute, Texas A&M Health Science Center, College Station, Texas 77843
10.1152/ajpheart.00727.2001.
The purpose of
this study was to test the hypothesis that regional brain blood flow
and vascular resistance are altered by acute and chronic head-down tail
suspension (HDT). Regional cerebral blood flow, arterial pressure,
heart rate, and vascular resistance were measured in a group of control rats during normal standing and following 10 min of HDT and in two
other groups of rats after 7 and 28 days of HDT. Heart rate was not
different among conditions, whereas mean arterial pressure was elevated
at 10 min of HDT relative to the other conditions. Total brain blood
flow was reduced from that during standing by 48, 24, and 27%
following 10 min and 7 and 28 days of HDT, respectively. Regional blood
flows to all cerebral tissues and the eyes were reduced with 10 min of
HDT and remained lower in the eye, olfactory bulbs, left and right
cerebrum, thalamic region, and the midbrain with 7 and 28 days of HDT.
Total brain vascular resistance was 116, 44, and 38% greater following
10 min and 7 and 28 days of HDT, respectively, relative to that during
control standing. Vascular resistance was elevated in all cerebral
regions with 10 min of HDT and remained higher than control levels in
most brain regions. These results demonstrate that HDT results in
chronic elevations in total and regional cerebral vascular resistance,
and this may be the underlying stimulus for the HDT-induced smooth
muscle hypertrophy of cerebral resistance arteries.
cerebral blood flow; microgravity; hindlimb unloading; unweighting
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