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Departments of 1 Biomedical Engineering, 2 Health and Kinesiology, and 3 Medical Physiology, Texas A&M University, College Station, Texas 77845
Previous studies have shown
that hindlimb unweighting of rats, a model of microgravity, reduces
evoked contractile tension of peripheral conduit arteries. It
has been hypothesized that this diminished contractile tension is the
result of alterations in the mechanical properties of these arteries
(e.g., active and passive mechanics). Therefore, the purpose of this
study was to determine whether the reduced contractile force of the
abdominal aorta from 2-wk hindlimb-unweighted (HU) rats results from a
mechanical function deficit resulting from structural vascular
alterations or material property changes. Aortas were isolated from
control (C) and HU rats, and vasoconstrictor responses to
norepinephrine (10
9-104 M) and AVP
(109-105 M) were tested in vitro. In a
second series of tests, the active and passive Cauchy stress-stretch
relations were determined by incrementally increasing the uniaxial
displacement of the aortic rings. Maximal Cauchy stress in response to
norepinephrine and AVP were less in aortic rings from HU rats. The
active Cauchy stress-stretch response indicated that, although maximum
stress was lower in aortas from HU rats (C, 8.1 ± 0.2 kPa; HU,
7.0 ± 0.4 kPa), it was achieved at a similar hoop stretch. There
were also no differences in the passive Cauchy stress-stretch response or the gross vascular morphology (e.g., medial cross-sectional area: C,
0.30 ± 0.02 mm2; HU, 0.32 ± 0.01 mm2) between groups and no differences in resting or basal
vascular tone at the displacement that elicits peak developed tension
between groups (resting tension: C, 1.71 ± 0.06 g; HU,
1.78 ± 0.14 g). These results indicate that HU does not
alter the functional mechanical properties of conduit arteries.
However, the significantly lower active Cauchy stress of aortas from HU
rats demonstrates a true contractile deficit in these arteries.
hindlimb unloading; norepinephrine; vasopressin; smooth muscle; cardiovascular; artery
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