Age-related changes in arterial wall mechanics and composition of NIA Fischer rats

Segments of carotid and tail arteries and descending thoracic aorta were obtained from the NIA colony of Fischer rats at ages 3, 12, 24 and 30 months. Measurements of pressure and diameter were made on intact cylindrical segments under conditions of active (147 mM K+) and passive (Ca2+-free and 2 mM EGTA) smooth muscle. These data were used to compute active and passive mechanics. Contiguous segments were used for the analysis of connective tissue, water and electrolyte contents. Passive stiffness of the carotid and tail arteries increased monotonically with increasing age. Collagen content in the aorta and tail artery generally increased with age, while elastin content decreased in the aorta and carotid artery. The ratio of collagen to elastin increased at all sites with age. Maximum values of active stress response (force development) increased from 3 to 12 months for the carotid artery, but decreased with age (at 24 and 30 months compared to 3 and 12-months) for the tail artery. Changes in relative cell content were such that active cellular force development was the same at all ages for the carotid artery but was smaller at 24 and 30 months compared to the younger animals for the tail artery. Decreased cellular force development by arterial smooth muscle is not an anatomically uniform finding in this animal model.