Sympathetic activity contributes to abdominal aortic compliance and wall distensibility in rats

Objective: The magnitude of the contribution of sympathetic tone to stiffness of large arteries varies with anatomical location in the arterial tree. In this study, the direct contribution of the sympathetic nervous system to abdominal aortic compliance and wall distensibility in the rat is quantified. Methods: Local abdominal aortic compliance (Ca) and wall distensibility (Wd) were quantified in 5 male Wistar-Kyoto rats before and following sympathectomy of the local arterial region. Aortic diameter was measured using B-mode ultrasound (ArtLab), and aortic blood pressure with an intravascular 1.2F pressure catheter. Blood pressure was altered with intravenous infusion of phenylephrine and sodium nitroprusside, for comparison of arterial tone at low (65-75 mmHg), resting anaesthetized (85-120 mmHg), and high (130-140 mmHg) mean blood pressure. Ca and Wd were determined from systolic (Ds) and diastolic (Dd) diameters and pulse pressure (PP): Ca = (Ds-Dd)/PP; Wd = Ca/Dd. Results: In all cases for resting anaesthetized and high mean blood pressure, Ca and Wd increased following sympathectomy of the abdominal aorta. No differences were present at low blood pressure. At resting anaesthetised blood pressure, Ca was greater following sympathectomy (Intact: 1.9 ± 0.3 mm/mmHg; Sympathectomy: 2.3 ± 0.3 mm/mmHg, p < 0.05) as was Wd at resting (Intact: 5.4×10−4 ± 1.1×10−4 mmHg−1; Sympathectomy: 6.6×10−4 ± 1.0×10−4 mmHg−1, p < 0.05) and high blood pressure (Intact: 3.5×10−4 ± 0.5×10−4mmHg −1; Sympathectomy: 4.5×10−4 ± 0.8×10−4 mmHg−1, p < 0.01). Inspection of the pressure-independent β stiffness index confirmed these findings. Conclusions: Sympathetic input to the abdominal aorta of rats contributes to the tone of the vessel, causing a decrease in Ca and Wd of the order of 17% and 22% respectively. This demonstrates that the input of the sympathetic system should be considered in conjunction with local endothelial derived nitric oxide pathways and structural components of the artery wall in the study of factors that can actively modulate large artery stiffness.