In spontaneously hypertensive rats alterations in aortic wall properties precede development of hypertension

In hypertension arterial wall properties do not necessarily depend on incre ased blood pressure alone. The present study investigates the relationship between the development of hypertension and thoracic aortic wall properties in 1.5-, 3-, and B-mo-old spontaneously hypertensive rats (SHR); Wistar-Ky oto rats (WKY) served as controls. During ketamine-xylazine anesthesia, com pliance and distensibility were assessed by means of a noninvasive ultrasou nd technique combined with invasive blood pressure measurements. Morphometr ic measurements provided in vivo media cross-sectional area and thickness, allowing the calculation of the incremental elastic modulus. Extracellular matrix protein contents were determined as well. Blood pressure was not sig nificantly different in 1.5-mo-old SHR and WKY, but compliance and distensi bility were significantly lower in SHR. Incremental elastic modulus was not significantly different between SHR and WKY at this age. Media thickness a nd media cross-sectional area were significantly larger in SHR than in WKY, but there was no consistent difference in collagen density and content bet ween the strains. Blood pressure was significantly higher in 3- and 6-mo-ol d SHR than in WKY, and compliance was significantly lower in SHR. The findi ngs in this study show that in SHR, in which hypertension develops over wee ks, alterations in functional aortic wall properties precede the developmen t of hypertension. The decrease in compliance and distensibility at a young age most likely results from media hypertrophy rather than a change in int rinsic elastic properties.