Remodeling of the arterial wall: Response to restoration of normal blood flow after flow reduction.

BACKGROUND: Although many studies have shown that arteries change diameter in response to chronic change in blood flow (BF), keeping wall shear stress (WSS) at physiologically normal levels, relatively little is known about the effects of flow restoration after flow reduction and also the role of vascular smooth muscle (VSM) during such a remodeling process. OBJECTIVE: To elucidate the biomechanical responses of the arterial wall to the restoration of normal BF after flow reduction and compare the results with our previous results observed in response to decreased BF alone. METHODS: Carotid artery BF in the Wistar rat was decreased by ligation and then restored to normal levels by release of the ligation. The effects of BF changes on the biomechanical properties of the carotid arterial wall were determined from measurements of diameters and pressures of excised artery segments. RESULTS: During BF reduction and restoration, WSS was maintained at physiological levels by changes in the internal diameter. No significant changes in the incremental elastic modulus were found in response to changes in BF. VSM tone was significantly enhanced during the changes in BF. CONCLUSIONS: Arteries change diameters in response to BF reduction and also flow restoration to normal after flow reduction, keeping WSS at physiologically normal levels. The lack of changes in vascular elasticity suggests that there were no significant changes in major wall constituents, such as elastin and collagen. VSM may play the dominant role in observed arterial remodeling and adaptation.

Remodeling of arterial wall: Response to changes in both blood flow and blood pressure.

Many studies have been performed on arterial responses to chronic changes in blood flow (BF) and blood pressure (BP). However, little is known about the effects of simultaneous changes in BF and BP. The present study was carried out to know biomechanical responses of arterial wall to the combination of increased BP, i.e. hypertension (HT), with lower or higher BF than normal, and the results were compared with those observed under normal BP, i.e. normotension (NT), combined with these BF conditions. Eight weeks old rats were subjected to BF and/or BP changes for 8 weeks until 16 weeks of age. Systemic HT was induced by the constriction of one of the renal arteries (Goldblatt HT), while BF in the CCA was reduced and increased by the constriction of the ipsilateral CCA and the ligation of the contralateral CCA, respectively. The internal diameter of the target CCA was significantly larger in higher BF groups than in lower BF ones irrespective of HT. Wall shear stress (WSS) was normalized by such compensatory changes in the diameter. Wall thickness was significantly larger in HT rats than in NT ones regardless of BF, and the wall hypertrophy contributed to restore wall hoop stress to normal level. Basal vascular tone, arterial stiffness, and wall elastic modulus were significantly larger in HT than in NT independently of BF changes. However, only in HT/lower BF group, WSS and vascular smooth muscle-activated vascular contraction were smaller than in the other groups, possibly because of wall hypertrophy induced by HT.