Adaptation of Conduit Artery Vascular Smooth Muscle Tone to Induced Hypertension

Abstract

We studied the changes in vascular smooth muscle (VSM) cell tone during the adaptation of rat common carotids to induced hypertension. Hypertension was induced in 8 week old male Wistar rats by total ligation of the aorta between the two kidneys. Mean blood pressure increased abruptly from 92 +/- 2mm Hg (mean +/- SE) to 145 +/- 4 mm Hg and remained constant thereafter. Rats were sacrificed 2, 4, 8, and 56 days after surgery and the left common carotid artery was excised for analysis. Pressure-diameter curves were measured in vitro under normal, maximally contracted, and totally relaxed VSM. The VSM tone was analyzed in terms of its basal tone (active stress at low strains) and its myogenic tone (increase in active stress at high strains). Our results show that the capacity of the VSM to develop maximal active stress is not altered in hypertension. Basal tone, however, increases rapidly in the acute hypertension phase (2-8 days postsurgery) and drops to nearly control values at 56 days postsurgery. Also, the onset of myogenic response decreases to lower strains following the step change in pressure, to be restored back to control levels at 56 days postsurgery. We conclude that VSM adaptation is most significant in the acute hypertension phase and acts as a first, rapid defense mechanism for the arterial wall. The VSM tone returns back to normal levels once the slower geometrical and structural remodeling is developed sufficiently to restore the biomechanical environment and function of the arterial wall to control levels.

Growth and remodeling in a thick-walled artery model: effects of spatial variations in wall constituents

“…When realistic distributions are included, the results given by the model agree quite well with the opening angle data of Liu and Fung (1988) and Fung and Liu (1989) (see Figs. 10 and 15), as well as the pressure-radius data of Berry et al (1975) and Fridez et al (2002) (see Fig. 4).…”

“…To illustrate the effects of muscle tone, active pressure-radius curves are shown for normal tone (λ a = 0.9) and maximum contraction (λ a = 0.6). For γ = 0.8 and C a = C a max = 15 kPa, numerical results are compared with experimental pressure-radius curves for the active and passive carotid artery of the rat (Fridez et al, 2002) and the passive thoracic aorta of the rat (Berry et al, 1975). For both arteries, the agreement between the theoretical and experimental results is reasonably good.…”

“…For an inflation test, the passive and active pressure-radius curves have the characteristic sigmoidal shape of the rat aorta and carotid artery (Berry et al, 1975;Fridez et al, 2002) (Fig. 4).…”

“…Curves for passive muscle, normal contraction (λ a = 0.9), and maximal contraction (λ a = 0.6) are shown for γ = 0.8. Experimental data are from Fridez et al (2002) for the rat carotid artery. Opening angle vs media-adventitia boundary location (γ) for homeostatic baseline model.…”

Complementary vasoactivity and matrix remodelling in arterial adaptations to altered flow and pressure

“…The most conspicuous consequence of hypertension in arteries is a thickening of the wall that tends to restore the circumferential stress towards its normal value (Wolinsky 1970;Matsumoto & Hayashi 1996;Fridez et al 2002;Hu et al 2007a,b). This is a more delayed manifestation of vascular adaptation compared with the instantaneous reduction in calibre observed in the case of reduced flow simply because the vessel must accumulate mass over some period.…”