Smooth Muscle Cell Relaxation Worsens Aortic Dilatation and Clinical Presentation in a BAPN/Angiotensin II-Induced Aortic Dissection Model in Rats

<b><i>Introduction:</i></b> Beta-aminopropionitrile (BAPN) administration is a chemically induced model for preclinical aortic pathologies research. Angiotensin II (AngII) has been widely used to promotes aortic dissections in mice. Here, we provide insight on a modified aortic dissection model in rats. The effect of smooth muscle cell (SMC) relaxation with vasodilators is studied in this model. <b><i>Methods:</i></b> Forty Sprague-Dawley rats were divided in 4 groups: control, isosorbide dinitrate (ISDN, 30 mg/kg/day) in the drinking water, BAPN (0.02%) in the food, BAPN + ISDN (same doses). Thoracic and abdominal aortic diameters were evaluated through transthoracic ultrasound echography. After 6 weeks, all rats were infused with AngII (1 mg/kg/day) subcutaneously. Survival and type of aortic events were numbered. Histological and histochemical analyses of aorta were performed. <b><i>Results:</i></b> Initial telesystolic ascending aorta diameters were equal in all groups and became significantly larger in the BAPN + ISDN group compared to the BAPN group (control: 3.37 ± 0.17 mm, ISDN: 3.49 ± 0.16 mm, BAPN: 3.53 ± 0.13 mm, BAPN + ISDN: 3.61 ± 0.16 mm, analysis of variance <i>p</i> &#x3c; 0.0001). BAPN followed by AngII infusion showed a significant lower survival rate (<i>p</i> = 0.029) and produced a large panel of aortic events. Association of ISDN and BAPN significantly reduces survival (<i>p</i> = 0.001) and provides more aortic events compared to BAPN alone (<i>p</i> = 0.031). In both BAPN-treated groups, orcein staining revealed split and dissected elastic fibers in the media, alcian blue staining showed mucoid degeneration of the aortic wall, and Perls-diaminobenzidine staining revealed an accumulation of Fe²⁺. <b><i>Conclusion:</i></b> SMC relaxation with ISDN increases aortic dilatation, worsens aortic prognosis, and reproduces human histological findings in a low-dose BAPN/AngII-induced aortic dissection model in rats.