The effects of hypothyroidism on the mechanical properties and histomorphological structure of the thoracic aorta.

This experimental study investigates the effects of hypothyroidism on the descending thoracic aorta. Hypothyroidism was induced in 20 male Wistar rats by administering 0.05% of 6-n propyl 2-thiouracil (PTU) in their drinking water for 8 weeks. Euthyroid rats were used as controls. Animals were sacrificed and longitudinal strips of the descending aorta were subjected to various preselected levels of stress in a uniaxial tensile-testing device. Analysis of stress-strain, elastic modulus-strain curves disclosed significant differences between groups, indicative of stiffer aortas in hypothyroid animals at the upper physiologic and higher levels of pressure. Remodeling of the aortic wall of hypothyroid animals revealed significant histological changes. The thoracic aorta of hypothyroid rats compared with that of euthyroid ones became stiffer at high strains, including the upper physiologic range, loosing part of its distensibility. Hypothyroidism was also associated with diameter enlargement and substantial lengthening of the aorta.