Morphological changes of the aorta and pulmonary artery in thoroughbred racehorses.

The aorta and extrapulmonary artery were examined pathologically in 33 thoroughbred racehorses ranging in age from 1 to 5 years. Many of the great vessels of these horses exhibited degenerative or sclerotic changes in the media with neither lipidosis nor deposits of cholesterol. The severe lesions were predominantly observed at the bifurcation of the pulmonary artery. The severity of the lesions in both the aorta and pulmonary artery appeared to be associated with the racing career of the racehorse rather than with increasing age. Histopathogenetically, the medial changes in the great vessels were probably initiated by ischaemia and/or oedema in their walls due to pathological disturbances of the vasa vasorum and their vasomotor nerves. Whether hypervitaminosis D plays a role in the condition in racehorses needs to be determined by further study.