Flow-induced vascular remodeling in the rat carotid artery diminishes with age

Vascular remodeling is regulated by a combination of hemodynamic, environmental, and genetic factors and may be influenced by age. To evaluate age-dependent remodeling in rats, we developed and used a quantitative highly reproducible model of carotid flow alteration. Fourteen juvenile (99+/-3 g) and 9 adult (199+/-5 g) male inbred Fischer rats underwent ligation of the left internal and external carotid arteries under anesthesia. Left common carotid blood flow immediately decreased by approximately 93%, whereas flow in the contralateral carotid increased by approximately 46%. After 4 weeks, the left carotid outer diameter (OD) significantly decreased in both juvenile and adult rats (as measured in vivo and by histological morphometry) compared with sham-operated rats. Changes in shear stress acutely mirrored the changes in blood flow. OD increased and shear stress returned to initial values after chronic exposure to increased flow in juvenile but not adult rats. To develop a simple quantitative index of remodeling that would not require killing the animals, we measured the OD in vivo and compared the ratio of right to left OD (OD ratio [ODR]) between groups. The initial ODR for all groups was approximately 1.0. After 4 weeks of altered flow, the ODR was significantly greater in juvenile than in adult rats (1.48+/-0.05 versus 1.29+/-0.04, respectively; P=.030), indicating that juvenile rats experienced more extensive remodeling than did the adult rats. We also found that unilateral carotid ligation caused a left versus right difference in endothelial NO synthase protein levels after 4 weeks that was not present in the sham-operated animals. Thus, the model described here shows that flow-induced vascular remodeling is dependent on age and supports the hypothesis that the driving force for remodeling involves shear stress and possibly NO. Because the model is quantitative, it allows dissection of the genetic factors that regulate remodeling in inbred rat strains.