Watanabe Hyperlipidemic Rabbit as a Model of Aortic Degeneration of the Medial Lamellar Elastin Unit

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Abstract
At age 3 years, WHHL rabbits are near the end of their lifespan, frequently dying from the progression of their hyperlipidemic disease from events such as myocardial infarction. Out of a colony of 20 three-year-old WHHL rabbits raised as part of a NIH breeding project, 2 rabbits actually died of a ruptured thoracic aortic aneurysm. The need for a model to study abdominal aortic aneurysm formation led us to explore further the abdominal aortic pathology in aged WHHL rabbits. Six rabbit abdominal aortas from 3-year-old WHHL rabbits were preserved in formalin, sectioned, and stained for elastin. These were compared to the same sections of six normalipidemic age matched New Zealand white (NZW) rabbits. There was significant (P ±. 001) destruction of the medial lamellar elastin unit in the aorta of the WHHL rabbits compared with the control NZW rabbits. Severe cholesterol deposits appeared to destroy the medial lamellae from the inside out. No definite aneurysm formation was seen in the abdominal aorta despite the significant changes in the medial lamellar elastin units. Thus, this model could be used to study the elastin degeneration of the media, but not necessarily abdominal aortic aneurysm formation.