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Department of Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242
To determine whether simulated microgravity in rats is
associated with vascular dysfunction, we measured responses of
isolated, pressurized mesenteric resistance artery segments (157- to
388-µm ID) to vasoconstrictors, pressure, and shear stress after
28-day hindlimb suspension (HS). Results indicated no
differences between HS and control (C) groups in 1) sensitivity
or maximal responses to vasoconstrictors (norepinephrine,
phenylephrine, serotonin, KCl); 2) ID, external diameter, or
ratio of wall thickness to ID; 3) distensibility; or 4)
vasodilatory responses to shear stress. Myogenic tone was attenuated
(P < 0.05) in HS arteries vs. C, as evidenced by 1)
decreased magnitude of tone in larger vessels (second-order branch off
superior mesenteric artery, 261- to 388-µm ID) at pressures 
40 mmHg
in the presence of phenylephrine (10
7 M) and
2) decreased magnitude of tone in smaller vessels (third-order branch off superior mesenteric artery, 157- to 277-µm ID), which exhibited spontaneous tone, at pressures 70 mmHg. This attenuation of
myogenic tone after HS could contribute to orthostatic intolerance because myogenic tone contributes to the overall tone of resistance arteries.
isolated vessels; pressure myograph; myogenic tone; shear stress; vasoconstriction
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