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Departments of 1 Health and Kinesiology and 2 Medical Physiology, Texas A&M University, College Station, Texas 77843
Hindlimb unloading (HU) of rats induces a
cephalic shift in body fluids. We hypothesized that the putative
increase in cranial fluid pressure and decrease in peripheral fluid
pressure would alter the morphology of resistance arteries from 2-wk HU
male Sprague-Dawley rats. To test this hypothesis, the cerebral
basilar, mesenteric, and splenic arteries were removed from control (C) and HU animals. The vessels were cannulated, and luminal pressure was
set to 60 cmH2O. The resistance
arteries were then relaxed with
10
4 M nitroprusside, fixed,
and cut into transverse cross sections (5 µm thick). Media
cross-sectional area (CSA), intraluminal CSA, media layer thickness,
vessel outer perimeter, and media nuclei number were determined. In the
basilar artery, both media CSA (HU 17,893 ± 2,539 µm2; C 12,904 ± 1,433 µm2) and thickness (HU 33.9 ± 4.1 µm; C 22.3 ± 3.2 µm) were increased with hindlimb
unloading (P < 0.05), intraluminal
CSA decreased (HU 7,816 ± 3,045 µm2; C 13,469 ± 5,500 µm2)
(P < 0.05), and vessel outer
perimeter and media nuclei number were unaltered. There were no
differences in mesenteric or splenic resistance artery morphology
between HU and C rats. These findings suggest that hindlimb
unloading-induced increases in cephalic arterial pressure and,
correspondingly, increases in circumferential wall stress result in the
hypertrophy of basilar artery smooth muscle cells.
cerebral blood flow; hindlimb unweighting; hypertrophy; morphology; vascular smooth muscle
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