Rabbit ear model of injury-induced arterial smooth muscle cell proliferation: Kinetics, reproducibility, and implications

Recently, considerable interest has focused on the vascular smooth muscle cell (SMC) response to injury, particularly as it relates to restenosis after angioplasty. In an effort to find an optimal experimental model of arterial SMC proliferation after injury, we examined the effects of external injury to the central artery of the rabbit ear and assessed the reproducibility, morphological changes, and time course of cellular proliferation after such an injury. With rabbits under general anesthesia, direct pressure was applied at two sites along the central artery of the ears of 19 New Zealand White rabbits. Rabbits were maintained on a diet of 2.4% fat and 0.001% cholesterol throughout the experiment. In seven rabbits examined after 21 days, marked SMC proliferation with neointimal formation was observed at all 28 sites (100%). Mean neointimal area, expressed as a percentage of the area of the tunica media, was 82±40% (range, 21-203%). Compared with the uninvolved artery displaced 2 mm from the injury site, mechanical crush caused a 38% increase in total vessel area (p<0.001), a 40% decrease in luminal area (p<0.002), and no change in the area of the media. Serial histological studies were performed 1-42 days after injury, using light and electron microscopy and bromodeoxyuridine immunohistochemistry. Beginning at day 3, activated medial SMCs were noted to migrate through defects in the internal elastic membrane, with a gradual increase in neointimal area between days 5 and 12. Peak DNA synthesis was identified in the media 5 days after injury, with proliferative activity shifting almost exclusively to the neointima thereafter. We conclude that mechanical crush injury is a potent stimulus for SMC proliferation. The method is simply employed, multiple lesions can be created in a single animal with high yield, and therapeutic end points can be easily quantified. The lesions so produced are superficial and easily accessible; therefore, agents with the potential to prevent SMC proliferation can be targeted locally by subcutaneous injection or topical application.