Functional spectroscopy approach to the assessment of nitric oxide storage in vascular tissues

Document Type

Conference Proceeding

Publication Title

Proceedings of SPIE - The International Society for Optical Engineering


Much attention has been devoted to the enzymatic production of nitric oxide (NO) by the endothelial layer lining blood vessel walls, which regulates among other things local vasodilatation and platelet adhesion. Considerably less attention, however, has been paid to the accumulation of NO-related products in the vascular wall itself. Such local storage of NO products could conceivably contribute to the local regulation of blood flow and provide additional anti-adhesive protection, if biochemically activated to regenerate NO. Since little is known about their chemical nature, concentrations, and possible role in vascular biology we sought to characterize those species basally present in rat aorta. To this end we developed a functional form of optical spectroscopy that allows us not only to identify NO-stores in intact tissues but also to monitor their production and disappearance in real-time. The method is based on the ability of NO stores to reversibly release NO when illuminated with light of particular wavelengths, which can be detected as a robust relaxation of vascular smooth muscle (photorelaxation). Characterization of NO-stores is achieved through a careful assessment of photorelaxation action spectra, taking into account the light scattering properties of the tissue, and of depletion of the NO-stores induced by exposure to controlled levels of light. This functional form of optical spectroscopy is applied to rat aortic tissue where the results suggest that the NO photolytically released from tissue stores originated from a low-molecular-weight RSNO as well as from nitrite. The significance of these findings to vascular physiology and pathophysiology is discussed.

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