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J Appl Physiol 99: 1624, 2005; doi:10.1152/japplphysiol.00875.2005
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POINT-COUNTERPOINT COMMENTS

In FMD, NO is actually "the middle man"

D. Walter Wray and Russell S. Richardson

Department of Medicine
Physiology Division
University of California San Diego
La Jolla, California 92093-0623
e-mail: dwray{at}ucsd.edu

ABSTRACT

This letter is in response to the Point:Counterpoint series "Flow-mediated dilation does/does not reflect nitric oxide-mediated endothelial function" that appeared in the September issue (vol. 99: 1233–1238, 2005; doi:10.1152/japplphysiol.00601.2005; http://jap.physiology.org/content/vol99/issue3/2005).

To the Editor: Having an ultrasound Doppler machine in our laboratory but hoping not to fall into the "delusion of grandeur" category of vascular researchers identified by Dr. Green (1), we offer the following thoughts regarding the importance of considering shear stimulus and subsequent nitric oxide (NO) release when evaluating flow-mediated dilation (FMD). Under the agreed-upon guidelines of a 5-min cuff occlusion below the site of measurement, we recently observed a diminution in brachial artery vasodilation in old subjects, insinuating an age-related decline in vascular function, which is in agreement with the current dogma (3). However, the reactive hyperemia in response to cuff occlusion was also diminished with age, so that the degree of brachial artery vasodilation was similar between younger and older subjects when normalized for the shear stimulus (unpublished observations). Although these observations do not resolve the present debate as to whether the FMD response reflects NO-mediated endothelial function, they do highlight the stimulus-response specificity which Dr. Tschakovsky outlines here and has published previously (2), emphasizing the importance of quantifying the shear stimulus as a part of the overall evaluation of FMD. Doing so may serve to prevent erroneous conclusions regarding changes in NO bioactivity that could simply be attributable to a dissimilar shear stimulus rather than underlying vascular dysfunction. With the recognition that varied shear will modulate the degree of NO release, we continue to value brachial FMD as a useful, noninvasive technique for evaluating endothelial function.

REFERENCES

  1. Green G; Tschakovsky ME and Pyke KE. Point:Counterpoint: Flow-mediated dilation does/does not reflect nitric oxide-mediated endothelial function. J Appl Physiol 99: 1233–1238, 2005.[Free Full Text]
  2. Pyke KE, Dwyer EM, and Tschakovsky ME. Impact of controlling shear rate on flow-mediated dilation responses in the brachial artery of humans. J Appl Physiol 97: 499–508, 2004.[Abstract/Free Full Text]
  3. Taddei S, Virdis A, Mattei P, Ghiadoni L, Gennari A, Fasolo CB, Sudano I, and Salvetti A. Aging and endothelial function in normotensive subjects and patients with essential hypertension. Circulation 91: 1981–1987, 1995.[Abstract/Free Full Text]




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
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Right arrow Alert me when this article is cited
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Google Scholar
Right arrow Articles by Wray, D. W.
Right arrow Articles by Richardson, R. S.
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PubMed
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Right arrow Articles by Wray, D. W.
Right arrow Articles by Richardson, R. S.

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