Background: Hypertension is a dangerous condition that precedes many cardiovascular events including myocardial infarction, stroke, transient cerebral ischemic attack and symptomatic aortoiliac occlusive disease. While it is universally accepted that arteries stiffen with age, the physiological reason for this is debated. In a previous study, by Dr. Shana Roach Watson it was shown that collagen fibers re-orient themselves in a circumferential direction, resulting in increased arterial stiffness. The study hypothesized that this collagen remodeling could be a result of decreased nitric oxide production.
Methods: This study measured nitric oxide in two different ways, indirectly via Immunoperoxidase staining for eNOS and directly via diaminofluorescein-2. In the design there were two timepoints: 6 weeks and 6 months. Groups of mice (n=5) were placed on either a high fat Western diet or a chow diet for 6 months. Young mice at 6 weeks of age on chow diet served as the baseline. For the immunoperoxidase staining procedure, 6 μm sections were stained via immunohistochemistry. For the diaminofluorescein-2 assay, the thoracic aorta (from the aortic arch to the diaphragm) was cut longitudinally and pinned en face onto culture dishes with a 3-millimeter-thick layer of black wax. They were stained with diaminofluorescein-2, and images were taken with the In Vivo Imaging System (IVIS).
Results: There was no significantt difference in endothelial Nitric Oxide Synthase (eNOS) expression between the groups for the immunoperoxidase staining. There was also no significant difference in Nitric Oxide release between the groups for the DAF-2 staining.
Conclusion: The lack of a significant decrease with age disproves our hypothesis that a decline in nitric oxide is responsible for the re-orientation of collagen fibers in the arterial wall
