Surgical thoracic sympathectomy induces structural and biomechanical remodeling of the thoracic aorta in a porcine model.

ABSTRACT

BACKGROUND: Sympathetic innervation exerts marked effects on vascular smooth muscle cells, including a short-term homeostatic (vasoconstrictor) and a direct trophic action promoting differentiation. However, the role of sympathetic nervous system in long-term structural and functional modulation of the aortic wall is yet undefined. METHODS: Six Landrace pigs underwent bilateral thoracic sympathectomy from the stellate to T8 ganglion, whereas 10 pigs underwent sham operation. Animals were sacrificed 3 mo postoperatively. Histometrical examination was performed on specimens from the thoracic (TA) and abdominal aorta (AA) utilizing an image-processing system. A uniaxial tensile tester was utilized for biomechanical evaluation; parameters of extensibility, strength, and stiffness of aortic tissue were calculated. RESULTS: Structural aortic remodeling of sympathectomized animals was observed, including increased inner aortic diameter in TA (15.3 ± 0.4 versus 10.4 ± 0.2 mm, P < 0.001) and AA (6.7 ± 0.3 versus 5.3 ± 0.2 mm, P = 0.002), and increased wall thickness in TA (2.0 ± 0.1 versus 1.6 ± 0.1 mm, P < 0.001) but not AA. Microscopic image analysis revealed increased elastin (TA 50.1 ± 1.1 versus 29.7% ± 0.6%, P < 0.001; AA 20.4 ± 2.1 versus 16.3% ± 0.6%, P = 0.03) and collagen density (only in TA 22.0 ± 0.9 versus 15.4% ± 0.5%, P < 0.001), and decreased smooth muscle density (TA 27.6 ± 1.3 versus 54.9% ± 0.7%, P < 0.001; AA 57.2 ± 1.5 versus 63.4% ± 0.8%, P < 0.001). Sophisticated biomechanical analysis demonstrated that following sympathectomy, TA was equally extensible but manifested augmented strength (1344 ± 73 versus 1071 ± 52 kPa, P = 0.004) and stiffness (6738 ± 478 versus 5026 ± 273 kPa, P = 0.003), in accordance with extracellular matrix protein accumulation in that region. Differences in the AA were non-significant. CONCLUSIONS: Chronic thoracic sympathetic denervation causes significant structural and biomechanical remodeling of the thoracic aorta. Possible clinical implications for patients undergoing thoracic sympathectomy or chronically treated with sympathetic blockers require further investigation.