Biomechanical properties and chemical composition of the aorta in genetic hypertensive rats.

Abstract

To study the alteration in the biomechanical properties of the thoracic aorta and its composition in young normotensive Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHR), and stroke-prone SHR (SHRSP). The in-vitro biomechanical properties of the aorta in 4- and 12-week-old SHRSP were determined by means of a tensile testing machine and compared with those of the SHR and WKY rats; in addition, a biochemical analysis of collagen, elastin and advanced glycation endproducts was performed. The aortic biomechanical properties were altered in the 4- and 12-week-old SHRSP, compared with age-matched WKY rats and SHR. The maximum stress in the 12-week-old SHRSP was reduced by 27% compared with the normotensive WKY rats, and by 26% compared with the SHR. The maximum strain values in the 4- and 12-week-old SHRSP were lower than those in the age-matched WKY rats, by 12 and 9% respectively, whereas this value in the 12-week-old SHR was significantly increased (by 26%) compared with the age-matched WKY rats. No differences were observed in the aortic contents of collagen and elastin between the SHRSP and SHR. However, the extractability of collagen by pepsin digestion in the 12-week-old SHRSP was lower than that in the age-matched SHR and WKY rats, and a significantly larger accumulation of advanced glycation endproducts was observed in the 12-week-old SHRSP than in the age-matched SHR and WKY rats, suggesting a greater formation of collagen-derived cross-links in SHRSP. From these results, we conclude that decreased aortic distensibility and mechanical strength values are partly related to the greater formation of collagen-derived cross-links in 12-week-old SHRSP, and that the mechanical properties in SHRSP may be the result not only of the larger formation of collagen-derived cross-links but also of primary defects, since the aortic mechanical strength value was decreased even in 4-week-old SHRSP.