Comparison of the visco-elastic properties of the tail artery in spontaneously hypertensive and normotensive rats

Abstract

Summary The quasistatic and dynamic elastic behaviour of the tail artery of male normotensive (NCR) and spontaneously hypertensive (SHR) rats was determined in vitro. The tone of the smooth muscle was enhanced by norepinephrine and diminished by papaverine. The circumferential wall stress was changed by varying the transmural pressure level. The experimental procedure was the same as that used in a previous investigation (Bauer and Pasch, 1971). The circumferential (tangential) elastic wall modulusE _t was calculated from the mean internal and external radii determined at each pressure level and from dynamic pressure-volume recordings in the frequency range between 0.03 and 20 Hz. The calculation was based on a formula valid for thick-walled, longitudinally constrained vessels. Results 1. The cross-sectional wall area is only slightly increased in SHR as compared with NCR. While under norepinephrine the quasistatic pressure-radius loops are virtually identical in NCR and SHR, the loops obtained under papaverine are shifted towards significantly greater radii in NCR than in SHR. It is concluded that in SHR there is a change in the structure of the non-muscular wall elements, but no essential alteration of the smooth muscle. 2. The dynamic elastic modulusE _d (real part ofE _t) increases with increasing wall stress σ _t . In NCR, theE _d − σ _t regression line for papaverine is significantly shifted towards higher moduli as compared with that for norepinephrine. This shift is only small in SHR. At a given wall stress,E _d is virtually independent of frequency within the range investigated in both NCR and SHR. 3. The loss modulus ωη_w (imaginary part ofE _t) shows virtually the same dependence on the wall stress asE _d. It increases markedly with frequency in NCR and SHR. There is a clear difference between the effects of spontaneous hypertension on the tail artery and on the peripheral resistance vessels.