Abstract 3546: Long-Term Effect of β-Receptor Blockade on the Mechanical Performance and Structure of the Thoracic Aorta in Rats
Aim: Aortic mechanical performance plays an important role in arterial homeostasis, constituting a prognostic factor for cardiovascular disease. The effect of sympathetic nerves on the structure and function of small and medium-sized vessels has been studied. The aim of this study was to examine the evolution of mechanical and structural changes of the thoracic aorta following prolonged β-blocker treatment.
Methods: Sixty-six healthy male Wistar rats were randomized in 4 groups. Group A was divided into subgroups A1 (n=6), A2 (n=6), and A3 (n=6), with animals receiving only water. In groups B (n=16), C (n=16), and D (n=16), propranolol was added in the drinking water (100 mg/kg/day). Animals of groups A1 and B, A2 and C, and A3 and D were sacrificed after 1, 2, and 3 months. Sufficiency of β-blockade was assessed by changes in heart rate in response to isoproterenol administration. The excised thoracic aorta was submitted to histological evaluation, with quantification of elastin, collagen, and smooth muscle cell content. Aortic specimens were submitted to biomechanical studies, and elastic modulus of the aortic wall was measured at low, physiologic, and high pressures.
Results: β-blockade was sufficient in treated animals. Data from subgroups A1, A2, and A3 were pooled together as control. Collagen content increased in the experimental groups compared to control (p<0.05), while smooth muscle cell content decreased (p<0.05), and elastin content remained unchanged. Elastic modulus of the aortic wall in the experimental groups increased with the duration of treatment compared to control at physiologic and high (p<0.05), but not at low pressures. The increase in elastic modulus at physiologic and high pressures correlated with the increase in collagen content among groups, while the non-significant differences at low pressures were attributed to the lack of difference in elastin content.
Conclusions: Blockade of β-adrenergic receptors induced changes in the mechanical properties and histological structure of the thoracic aorta, with the vessel becoming progressively stiffer at physiologic and high pressures due to the increased collagen content. Changes in aortic stiffness, in response to β-blocker treatment, merit further clinical investigation.