Arch Hellen Med, 22(1), January-February 2005, 54-65
Model system development
E. KEFALOYANNIS,1 D.P. SOKOLIS,2 M. KOULOUKOUSSA,3 S. ΗAVAKI,3 E. MARINOS,3 P.E. KARAYANNACOS2
OBJECTIVE Τhe purpose of this study was the development of a model system for the investigation of the histological structure of the aortic wall when subjected to pre-selected levels of stress.
METHOD Ten white male New Zealand rabbits with a body weight of 3,600 g were used for this study. Through a midline thoracic incision, the descending thoracic aorta was resected and cleaned of surrounding tissues. Longitudinal strips of fixed dimensions were acquired and subjected to uniaxial tensile testing on a Vitrodyne V1000 Universal Tester. Various pre-selected levels of stress were applied to the specimens in their longitudinal axis. Some were not subjected to mechanical stress and served for reference. The tissue was then fixed under stress in Karnovsky's solution for a minimum of 90 min and embedded in paraffin; transverse and longitudinal 5-μm sections were taken. Verhoeff's stain was used for elastin and Masson's trichrome stain for collagen. The histological study was carried out using a Zeiss Αxiolab light microscope.
RESULTS The stress-strain and elastic modulus-stress curves were divided into three parts, referring to low, physiologic and high stresses. At low levels of stress, the elastic modulus of the aortic wall was comparable to that of elastin, while at high levels to that of collagen. In the longitudinal histological sections, mechanical stress caused gradual straightening of elastin fibers and collagen bundles with increase in stress levels. The waviness of elastin and collagen remained invariant at all levels of longitudinally applied mechanical stress in the transverse sections.
CONCLUSIONS A correlation was shown between the morphologic alterations occurring in the aortic wall and the level of applied stress. The morphometric analysis of the remodeling observed in the aortic wall upon the application of stress contributes to a clear understanding of the mechanical behavior of the aorta. The remodeling of the histological components of the aorta results in a more uniform distribution of stresses within the aortic wall, and helps to explain its contribution to homeostasis of the circulatory system.
Key words: Elastic properties, Histologic structure, Morphometry.