Effects of simulated microgravity on vasoconstrictor and mechanical properties of the rat abdominal aorta
Date
2002
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Texas A&M University
Abstract
In humans and rats, microgravity induces adaptations within the cardiovascular system that appear to include modifications in peripheral vascular reactivity. Rodent hindlimb unweighting (HU) has been used to model putative adaptations that occur in humans in microgravity. Previous studies have shown that HU reduces evoked contractile tension of peripheral conduit arteries. It has been hypothesized that the diminished contractile tension is the result of 1) an increase production of nitric oxide (NO) via an inducible nitric oxide synthase (iNOS) mechanism and 2) alterations in the mechanical properties of the vessels, i.e., increased compliance. Using the rat HU model, this study was designed to determine whether the reduced contractile force of the abdominal aorta results from enhanced NO release through an iNOS mechanism and/or if there exists a mechanical function deficit as a result of structural alterations. Rats (400-450g) were either hindlimb unweighted for 2 weeks (HU rats) or maintained normal weight-bearing activity (control rats). Aortas were isolated and vasoconstrictor responses to norepinephrine (NE, 10-⁹ - 10-⁴ M) and arginine vasopressin (AVP, 10-⁹ - 10-⁵ M) were tested in vitro either in the presence or absence of the iNOS inhibitor aminoguanidine (0.3mM). Active and passive stress-stretch relations were investigated by an extension response. Maximal tension developed in response to NE and AVP was less in aortic rings from HU rats, and the iNOS inhibitor did not normalize this difference. Also, there were no differences in the passive stress-stretch response between the two groups, which support the unaltered morphology observed of HU aortas. Finally, both the length-developed tension and active stress-stretch response indicated that maximum developed tension and maximum stress were achieved at similar uniaxial displacement and stretch, respectively, which supports the conclusion that HU does not alter the functional mechanical properties of aortic arteries. However, the lower developed tension and active Cauchy stress by HU aortas does confirm a contractile deficit.
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Includes bibliographical references (leaves 35-38).
Issued also on microfiche from Lange Micrographics.
Includes bibliographical references (leaves 35-38).
Issued also on microfiche from Lange Micrographics.
Keywords
biomedical engineering., Major biomedical engineering.