Arch Hellen Med, 24(3), May-June 2007, 291-300
Histological changes of the aortic wall under mechanical stress
E.M. KEFALOYANNIS,1 D.P. SOKOLIS,2 M. KOULOUKOUSSA,1 E. MARINOS,1 H. BOUDOULAS,2 P.E. KARAYANNACOS2
OBJECTIVE It is known that the aorta responds to changes in intraluminal pressures by changes in its dimensions. The aim of this study was the investigation of the structural-histological remodeling of the aortic wall as a result of the action of different levels of mechanical stress.
METHOD Thirty-five white male New Zealand rabbits of the same age were used. The descending thoracic aorta was removed following median sternotomy and longitudinal strips were obtained, which were subjected to pre-selected levels of mechanical stress on a uniaxial tensile-testing device. Specimens were fixed under various levels of stress in Karnovsky's solution, dehydrated, and embedded in paraffin. The procedure was repeated at different levels of stress that covered the entire range of stresses potentially applied to the vessel wall, from zero to very high levels. The orientation of elastin and collagen fibers in the tunica media was examined in transverse and longitudinal sections of the vessel. For light microscopy examination, specimens were stained with Verhoeff's elastica for identification of elastin and with Sirius red for identification of collagen.
RESULTS The elastic lamellae under zero stress were wavy and distributed along both the longitudinal and circumferential directions of the vessel, whereas collagen was coiled and appeared in the form of bundles with precise circumferential orientation and in the form of interlaced fibrils. In longitudinal sections, the elastic lamellae gradually unfolded at low and were almost straight at physiologic and high stresses, while collagen fibrils reoriented in the longitudinal axis at low, started uncoiling at physiologic, and straightened massively at high stresses. In transverse sections, the waviness of elastic lamellae and circumferentially distributed collagen bundles remained invariant with increasing longitudinally applied stress.
CONCLUSIONS These microstructural changes indicate that elastin is activated at low and physiologic, and collagen at physiologic and high stresses. A correlation is confirmed between the histological remodeling of the aortic wall and the level of applied stress, and an explanation is provided for the mechanism by which the histological microstructure of the aorta responds to changes in intraluminal pressures.
Key words: Aorta, Elastin, Collagen, Mechanical stress.