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The Mechanical Performance and Histomorphological Structure of the Descending Aorta in Hyperthyroidism

Center for Experimental Surgery, Foundation of Biomedical Research, Academy of Athens, Greece, konmoulakakis{at}yahoo.gr, Laboratory for Experimental Surgery and Surgical Research, School of Medicine, University of Athens, Greece

Dimitrios P. Sokolis, PhD

Center for Experimental Surgery, Foundation of Biomedical Research, Academy of Athens, Greece

Despina N. Perrea, PhD

Laboratory for Experimental Surgery and Surgical Research, School of Medicine, University of Athens, Greece

Theodosios Dosios, MD, FACS, FETCS

Laboratory for Experimental Surgery and Surgical Research, School of Medicine, University of Athens, Greece

Ismene Dontas, DVM, PhD

Laboratory for Experimental Surgery and Surgical Research, School of Medicine, University of Athens, Greece

Maria V. Poulakou, BSc

Laboratory for Experimental Surgery and Surgical Research, School of Medicine, University of Athens, Greece

Constantinos A. Dimitriou, MSc

Center for Experimental Surgery, Foundation of Biomedical Research, Academy of Athens, Greece

George Sandris, BSc

Center for Experimental Surgery, Foundation of Biomedical Research, Academy of Athens, Greece

Panayotis E. Karayannacos, MD, PhD

Center for Experimental Surgery, Foundation of Biomedical Research, Academy of Athens, Greece

Thyroid hormones decrease systemic vascular resistance by directly affecting vascular smooth muscle relaxation. There is limited literature about their effect on the mechanical performance of the aortic wall. Therefore, the authors determined the influence of hyperthyroidism on the mechanical properties and histomorphological structure of the descending thoracic aorta in rats. Severe hyperthyroidism was induced in 20 male Wistar rats by administering L-thyroxine (T₄) in their drinking water for 8 weeks; age-matched normal euthyroid rats acted as controls. Animals were sacrificed, and the mechanical and histomorphometrical characteristics of the descending thoracic aorta were studied. The aortic wall of hyperthyroid rats was stiffer than that of euthyroid animals at the upper physiologic levels of stress or strain (p < 0.05) but less stiff at the lower physiologic and lower levels (p < 0.05). The aorta of hyperthyroid animals compared with that of euthyroid ones showed an increase of the internal and external diameters (p < 0.05), the media area (p < 0.05), the number of smooth muscle cell nuclei (p < 0.05), and the collagen density (p < 0.05) and a decrease in the elastin laminae thickness (p < 0.001) and elastin density (p < 0.001). In hyperthyroid rats, the aortic wall was stiffer at the upper physiologic and higher levels of stress and strain. These changes correlated with microstructural changes of the aortic wall. The coexistence of hyperthyroidism with disease states or clinical conditions that predispose to increased arterial pressure may be associated with increased arterial stiffness and have undesirable consequences on the mechanical performance of the thoracic aorta and hemodynamic homeostasis. These changes could lead to an increased risk for developing vascular complications.

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