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Articles in PresS, published online ahead of print October 4, 2002
J Appl Physiol, 10.1152/jap.00734.2002
Submitted on August 7, 2002
Accepted on September 21, 2002
1 Department of Biomedical Engineering, Texas A&M University, College Station, TX, USA
2 Department of Health and Kinesiology, Texas A&M University, College Station, TX, USA; Department of Medical Physiology, Texas A&M University, College Station, TX, USA
* To whom correspondence should be addressed. E-mail: mdd{at}hlkn.tamu.edu.
Previous studies have shown that hindlimb unweighting (HU) 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 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 (NE, 10-9 - 10-4 M) and arginine vasopressin (AVP, 10-9 - 10-5 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 NE 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 which elicits peak developed tension (Lmax) 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.
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